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Axel Polleres

Publications

You can also check my publication entries at DBLP and hits in Google Scholar.

If you need bibtex entries, check out my publications in BibBase.


2013


[AP13] Albin Ahmeti and Axel Polleres. SPARQL update under RDFS entailment in fully materialized and redundancy-free triple stores. In 2nd International Workshop on Ordering and Reasoning (OrdRing 2013), Sydney, Australia, October 2013. To appear. [ .pdf ]
Processing the dynamic evolution of RDF stores has recently been standardized in the SPARQL 1.1 Update specification. However, computing answers entailed by ontologies in triple stores is usually treated orthogonal to updates. Even the W3C's recent SPARQL 1.1 Update language and SPARQL 1.1 Entailment Regimes specifications explicitly exclude a standard behavior how SPARQL endpoints should treat entailment regimes other than simple entailment in the context of updates. In this paper, we take a first step to close this gap, by drawing from query rewriting techniques explored in the context of DL-Lite. We define a fragment of SPARQL basic graph patterns corresponding to (the RDFS fragment of) DL-Lite and the corresponding SPARQL Update language discussing possible semantics along with potential strategies for implementing them. We treat both (i) reduced RDF Stores, that is, redundancy-free RDF stores that do not store any RDF triples (corresponding to DL Lite ABox statements) entailed by others already, and (ii) materialized RDF stores, which store all entailed triples explicitly.

[GPM13] Marina Gueroussova, Axel Polleres, and Sheila A. McIlraith. SPARQL with qualitative and quantitative preferences. In 2nd International Workshop on Ordering and Reasoning (OrdRing 2013), Sydney, Australia, October 2013. To appear. Position Paper. [ .pdf ]
The volume and diversity of data that is queriable via SPARQL and its increasing integration motivate the desire to query SPARQL information sources via the specification of preferred query outcomes. Such preference-based queries support the ordering of query outcomes with respect to a user's measure of the quality of the response. In this position paper we argue for the incorporation of preference queries into SPARQL. We propose an extension to the SPARQL query language that supports the specification of qualitative and quantitative preferences over query outcomes and examine the realization of the resulting preference-based queries via off-the-shelf SPARQL engines.

[BPS13] Stefan Bischof, Axel Polleres, and Simon Sperl. City data pipeline - a system for making open data useful for cities. In Steffen Lohmann, editor, Proceedings of the I-SEMANTICS 2013 Posters & Demonstrations Track, volume 1026 of CEUR Workshop Proceedings, pages 45-49, Graz, Austria, September 2013. CEUR-WS.org. [ .pdf ]
Some cities publish data in an open form. But even more cities can profit from the data that is already available as open or linked data. Unfortunately open data of different sources is usually given also in different heterogeneous data formats. With the City Data Pipeline we aim to integrate data about cities in a common data model by using Semantic Web technologies. Eventually we want to support city officials with their decisions by providing automated analytics support.

[SP13] Simon Steyskal and Axel Polleres. Mix'n'match: An alternative approach for combining ontology matchers. In 12th International Conference on Ontologies, DataBases, and Applications of Semantics (ODBASE 2013), Lecture Notes in Computer Science (LNCS), Graz, Austria, September 2013. Springer. Short paper.
The existence of a standardized ontology alignment format promoted by the Ontology Alignment Evaluation Initiative (OAEI) potentially enables different ontology matchers to be combined and used together. Along these lines, we present a novel architecture for combining ontology matchers based on iterative calls of off-the-shelf matchers that exchange information in the form of reference mappings in this standard alignment format. However, we argue that only a few of the matchers contesting in the past years' OAEI campaigns actually allow the provision of reference alignments to support the matching process. We bypass this lacking functionality by introducing an alternative approach for aligning results of different ontology matchers using simple URI replacement in the aligned ontologies. We experimentally prove that our iterative approach benefits from this emulation of reference alignments.

[PFSF13] Axel Polleres, Melanie Frühstück, Gottfried Schenner, and Gerhard Friedrich. Debugging non-ground ASP programs with choice rules, cardinality constraints and weight constraints. In Pedro Cabalar and Tran Cao Son, editors, Proceedings of the 12th International Conference on Logic Programming and Nonmonotonic Reasoning (LPNMR-2013), volume 8148 of Lecture Notes in Computer Science (LNCS), pages 452-464, Corunna, Spain, September 2013. Springer. [ .pdf ]
When deploying Answer Set Programming (ASP)in an industrial context, for instance for (re-)configuration (Friedrich et al., 2011), knowledge engineers need debugging support on non-ground programs. Current approaches to ASP debugging, however, do not cover extended modeling features of ASP, such as choice rules, conditional cardinality and weight constraints. To this end, we encode non-ground ASP programs using extended modeling features into normal logic progams; this encoding extends existing encodings for the case of ground programs to the non-ground case. We subsequently deploy this translation in order to extend ASP debugging for non-ground normal logic programs. We have implemented and tested the approach and provide evaluation results.

[PHDU13] Axel Polleres, Aidan Hogan, Renaud Delbru, and Jürgen Umbrich. RDFS & OWL reasoning for linked data. In Sebastian Rudolph, Georg Gottlob, Ian Horrocks, and Frank van Harmelen, editors, Reasoning Web. Semantic Technologies for Intelligent Data Access (Reasoning Web 2013), volume 8067 of Lecture Notes in Computer Science (LNCS), pages 91-149. Springer, Mannheim, Germany, July 2013. [ .pdf ]
Linked Data promises that a large portion of Web Data will be usable as one big interlinked RDF database against which structured queries can be answered. In this lecture we will show how reasoning - using RDF Schema (RDFS) and the Web Ontology Language (OWL) - can help to obtain more complete answers for such queries over Linked Data. We first look at the extent to which RDFS and OWL features are being adopted on the Web. We then introduce two high-level architectures for query answering over Linked Data and outline how these can be enriched by (lightweight) RDFS and OWL reasoning, enumerating the main challenges faced and discussing reasoning methods that make practical and theoretical trade-offs to address these challenges. In the end, we also ask whether or not RDFS and OWL are enough and discuss numeric reasoning methods that are beyond the scope of these standards but that are often important when integrating Linked Data from several, heterogeneous sources.

[BP13] Stefan Bischof and Axel Polleres. RDFS with attribute equations via SPARQL rewriting. In Philipp Cimiano, Oscar Corcho, Valentina Presutti, Laura Hollink, and Sebastian Rudolph, editors, The Semantic Web: Semantics and Big Data - Proceedings of the 10th ESWC (ESWC2013), volume 7882 of Lecture Notes in Computer Science (LNCS), pages 335-350, Montpellier, France, May 2013. [ .pdf ]
In addition to taxonomic knowledge about concepts and properties typically expressible in languages such as RDFS and OWL, implicit information in an RDF graph may be likewise determined by arithmetic equations. The main use case here is exploiting knowledge about functional dependencies among numerical attributes expressible by means of such equations. While some of this knowledge can be encoded in rule extensions to ontology languages, we provide an arguably more flexible framework that treats attribute equations as first class citizens in the ontology language. The combination of ontological reasoning and attribute equations is realized by extending query rewriting techniques already successfully applied for ontology languages such as (the DL-Lite-fragment of) RDFS or OWL, respectively. We deploy this technique for rewriting SPARQL queries and discuss the feasibility of alternative implementations, such as rule-based approaches.

[BCL+13] Olivier Boissier, Marco Colombetti, Michael Luck, John-Jules Meyer, and Axel Polleres. Norms, organizations, and semantics. The Knowledge Engineering Review, 28(1):107-116, March 2013. [ http ]
This paper integrates the responses to a set of questions from a distinguished set of panelists involved in a discussion at the Agreement Technologies workshop in Cyprus in December 2009. The panel was concerned with the relationship between the research areas of semantics, norms, and organizations, and the ways in which each may contribute to the development of the others in support of next generation agreement technologies.

[SZF+13] Ratnesh Sahay, Antoine Zimmermann, Ronan Fox, Axel Polleres, and Manfred Hauswirth. A formal investigation of semantic interoperability of HCLS systems. In Miguel-Angel Sicilia and Pablo Serrano-Balazote, editors, Interoperability in Healthcare Information Systems: Standards, Management, and Technology. IGI Global, February 2013. [ http ]
Semantic interoperability facilitates Health Care and Life Sciences (HCLS) systems in connecting stakeholders (e.g., patients, physicians, pharmacies) at various levels as well as ensures seamless use of healthcare resources (e.g., data, schema, applications). Their scope ranges from local (within, e.g., hospitals or hospital networks) to regional, national and cross-border. The use of semantics in delivering interoperable solutions for HCLS systems is weakened by fact that an Ontology Based Information System (OBIS) has restrictions in modeling, aggregating, and interpreting global knowledge (e.g., terminologies for disease, drug, clinical event) in conjunction with local information (e.g., policy, profiles). This chapter presents an example-scenario that shows such limitations and recognizes that enabling two key features, namely the type and scope of knowledge, within a knowledge base could enhance the overall effectiveness of an OBIS. We provide the idea of separating knowledge bases in types (e.g., general or constraint knowledge) with scope (e.g., global or local) of applicability. Then, we propose two concrete solutions on this general notion. Finally, we describe open research issues that may be of interest to knowledge system developers and broader research community.

[PW13] Axel Polleres and Johannes Wallner. On the relation between sparql1.1 and answer set programming. Journal of Applied Non-Classical Logics (JANCL), 23(1-2):159-212, 2013. Special issue on Equilibrium Logic and Answer Set Programming. [ http ]
In the context of the emerging Semantic Web and the quest for a common logical framework underpinning its architecture, the relation of rule-based languages such as Answer Set Programming (ASP) and ontology languages such as OWL has attracted a lot of attention in the literature over the past years. With its roots in Deductive Databases and Datalog though, ASP shares much more commonality with another Semantic Web standard, namely the query language SPARQL. In this paper, we take the forthcoming approval of the SPARQL1.1 standard by the World Wide Web consortium (W3C) as an opportunity to introduce this standard to the Logic Programming community by providing a translation of SPARQL1.1 into ASP. In this translation, we explain and highlight peculiarities of the new W3C standard. Along the way, we survey existing literature on foundations of SPARQL and SPARQL1.1, and also combinations of SPARQL with ontology and rules languages. Thereby, apart from providing means to implement and support SPARQL natively within Logic Programming engines and particularly ASP engines, we hope to pave the way for further research on a common logical framework for Semantic Web languages, including query languages, from an ASP point of view.

[Pol13] Axel Polleres. Agreement technologies and the semantic web. In Sascha Ossowski, editor, Agreement Technologies, volume 8 of Law, Governance and Technology Series, pages 57-68. Springer, January 2013. [ http ]
In this chapter we discuss the relationship between Agreement Technologies and the Semantic Web, especially focusing on how Semantic Web standards play a role in the Agreement Technologies stack, but also issues related to Linked Data and the Web of Data. We start the chapter with an account of Semantic Web standards. Then the scientific foundations of Semantic Web standards are discussed. Finally, we relate the work on semantic technologies to other fields of Agreement Technologies, from the point of view of Semantic Web standards.

[FMPG+13] Javier D. Fernández, Miguel A. Martinez-Prieto, Claudio Gutiérrez, Axel Polleres, and Mario Arias. Binary RDF Representation for Publication and Exchange (HDT). Journal of Web Semantics (JWS), 19(2), 2013. [ http ]
The current Web of Data is producing increasingly large RDF data sets. Massive publication efforts of RDF data driven by initiatives like the Linked Open Data movement, and the need to exchange large data sets has unveiled the drawbacks of traditional RDF representations, inspired and designed by a document-centric and human-readable Web. Among the main problems are high levels of verbosity/redundancy and weak machine-processable capabilities in the description of these data sets. This scenario calls for efficient formats for publication and exchange. This article presents a binary RDF representation addressing these issues. Based on a set of metrics that characterizes the skewed structure of real-world RDF data, we develop a proposal of an RDF representation that modularly partitions and efficiently represents three components of RDF data sets: Header information, a Dictionary, and the actual Triples structure (thus called HDT). Our experimental evaluation shows that data sets in HDT format can be compacted by more than fifteen times as compared to current naive representations, improving both parsing and processing while keeping a consistent pub- lication scheme. Specific compression techniques over HDT further improve these compression rates and prove to outperform existing compression solutions for efficient RDF exchange.

[BAACP13] Carlos Buil-Aranda, Marcelo Arenas, Oscar Corcho, and Axel Polleres. Federating queries in SPARQL1.1: Syntax, semantics and evaluation. Journal of Web Semantics (JWS), 18(1), 2013. [ http ]
Given the sustained growth that we are experiencing in the number of SPARQL endpoints available, the need to be able to send federated SPARQL queries across these has also grown. To address this use case, the W3C SPARQL working group is defining a federation extension for SPARQL 1.1 which allows for combining graph patterns that can be evaluated over several endpoints within a single query. In this paper, we describe the syntax of that extension and formalize its semantics. Additionally, we describe how a query evaluation system can be implemented for that federation extension, describing some static optimization techniques and reusing a query engine used for data-intensive science, so as to deal with large amounts of intermediate and final results. Finally we carry out a series of experiments that show that our optimizations speed up the federated query evaluation process.

[PPSW13] Reinhard Pichler, Axel Polleres, Sebastian Skritek, and Stefan Woltran. Complexity of redundancy detection on rdf graphs in the presence of rules, constraints, and queries. Semantic Web - Interoperability, Usability, Applicability, 4(4), 2013. [ .pdf ]
Based on practical observations on rule-based inference on RDF data, we study the problem of redundancy elimination on RDF graphs in the presence of rules (in the form of Datalog rules) and constraints, (in the form of so-called tuple-generating dependencies), and with respect to queries (ranging from conjunctive queries up to more complex ones, particularly covering features of SPARQL, such as union, negation, or filters). To this end, we investigate the influence of several problem parameters (like restrictions on the size of the rules, the constraints, and/or the queries) on the complexity of detecting redundancy. The main result of this paper is a fine-grained complexity analysis of both graph and rule minimisation in various settings.


2012


[RPF+12] Anna Ryabokon, Axel Polleres, Gerhard Friedrich, Andreas Falkner, Alois Haselböck, and Herwig Schreiner. (re)configuration using web data: a case study on the reviewer assignment problem. In Markus Krötzsch and Umberto Straccia, editors, Web Reasoning and Rule Systems - 6th International Conference, RR2012, volume 7497 of Lecture Notes in Computer Science (LNCS), pages 258-261, Vienna, Austria, September 2012. Springer. Short paper. [ .pdf ]
Constraint-based configuration is - on the one hand - one of the classical problem domains in AI and also in industrial practice. Additional problems arise, when configuration objects come from an open environment such as the Web, or in case of a reconfiguration. On the other hand, (re)configuration is a reasoning task very much ignored in the current (Semantic) Web reasoning literature, despite (i) the increased availability of structured data on the Web, particularly due to movements such as the Semantic Web and Linked Data, (ii) numerous practically relevant tasks in terms of using Web data involve (re)configuration. To bridge these gaps, we discuss the challenges and possible approaches for reconfiguration in an open Web environment, based on a practical use case leveraging Linked Data as a “component catalog” for configuration. In this paper, we present techniques to enhance existing review management systems with (re)configuration facilities and provide a practical evaluation.

[UHPD12] Jürgen Umbrich, Aidan Hogan, Axel Polleres, and Stefan Decker. Improving the recall of live linked data querying through reasoning. In Markus Krötzsch and Umberto Straccia, editors, Web Reasoning and Rule Systems - 6th International Conference, RR2012, volume 7497 of Lecture Notes in Computer Science (LNCS), pages 188-204, Vienna, Austria, September 2012. Springer. [ .pdf ]
Linked Data principles allow for processing SPARQL queries on-the-fly by dereferencing URIs. Link-traversal query approaches for Linked Data have the benefit of up-to-date results and decentralised execution, but operate only on explicit data from dereferenced documents, affecting recall. In this paper, we show how inferable knowledge - specifically that found through owl:sameAs and RDFS reasoning - can improve recall in this setting. We first analyse a corpus featuring 7 million Linked Data sources and 2.1 billion quadruples: we (1) measure expected recall by only considering dereferenceable information, (2) measure the improvement in recall given by considering rdfs:seeAlso links as previous proposals did. We further propose and measure the impact of additionally considering (3) owl:sameAs links, and (4) applying lightweight RDFS reasoning for finding more results, relying on static schema information. We evaluate different configurations for live queries covering different shapes and domains, generated from random walks over our corpus.

[Pol12] Axel Polleres. How (well) do datalog, SPARQL and RIF interplay? In Pablo Barceló and Reinhard Pichler, editors, Datalog in Academia and Industry - Second International Workshop, Datalog 2.0, volume 7494 of Lecture Notes in Computer Science (LNCS), pages 27-30. Springer, September 2012. Invited tutorial, slides available at http://www.polleres.net/presentations/20120913Datalog20_Tutorial.pdf. [ http ]
In this tutorial we will give an overview of the W3C standard query language for RDF - SPARQL - and its relation to Datalog as well as on the interplay with another W3C standard closely related to Datalog, the Rule Interchange Format (RIF). As we will learn - while these three interplay nicely on the surface and in academic research papers - some details within the W3C specs impose challenges on seamlessly integrating Datalog rules and SPARQL.

[LKZ+12] Nuno Lopes, Sabrina Kirrane, Antoine Zimmermann, Axel Polleres, and Alessandra Mileo. A Logic Programming approach for Access Control over RDF. In Agostino Dovier and Vítor Santos Costa, editors, Technical Communications of the ICLP 2012, volume 17 of LIPIcs, pages 381-392, Budapest, Hungary, September 2012. Schloss Dagstuhl - Leibniz-Zentrum fuer Informatik. Short paper. [ .pdf ]
The Resource Description Framework (RDF) is an interoperable data representation format suitable for interchange and integration of data, especially in Open Data contexts. However, RDF is also becoming increasingly attractive in scenarios involving sensitive data, where data protection is a major concern. At its core, RDF does not support any form of access control and current proposals for extending RDF with access control do not fit well with the RDF representation model. Considering an enterprise scenario, we present a modelling that caters for access control over the stored RDF data in an intuitive and transparent manner. For this paper we rely on Annotated RDF, which introduces concepts from Annotated Logic Programming into RDF. Based on this model of the access control annotation domain, we propose a mechanism to manage permissions via application-specific logic rules. Furthermore, we illustrate how our Annotated Query Language (AnQL) provides a secure way to query this access control annotated RDF data.

[HUH+12] Aidan Hogan, Jürgen Umbrich, Andreas Harth, Richard Cyganiak, Axel Polleres, and Stefan Decker. An empirical survey of linked data conformance. Journal of Web Semantics (JWS), 14:14-44, July 2012. [ .pdf ]
There has been a recent, tangible growth in RDF published on the Web in accordance with the Linked Data principles and best practices, the result of which has been dubbed the “Web of Data”. Linked Data guidelines are designed to facilitate ad hoc re-use and integration of conformant structured data-across the Webby consumer applications; however, thus far, systems have yet to emerge that convincingly demonstrate the potential applications for consuming currently available Linked Data. Herein, we compile a list of fourteen concrete guidelines as given in the “How to Publish Linked Data on the Web” tutorial. Thereafter, we evaluate conformance of current RDF data providers with respect to these guidelines. Our evaluation is based on quantitative empirical analyses of a crawl of  4 million RDF/XML documents constituting over 1 billion quadruples, where we also look at the stability of hosted documents for a corpus consisting of nine monthly snapshots from a sample of 151 thousand documents. Backed by our empirical survey, we provide insights into the current level of conformance with respect to various Linked Data guidelines, enumerating lists of the most (non-)conformant data providers. We show that certain guidelines are broadly adhered to (esp. use HTTP URIs, keep URIs stable), whilst others are commonly overlooked (esp. provide licencing and human-readable meta-data). We also compare PageRank scores for the data-providers and their conformance to Linked Data guidelines, showing that both factors negatively correlate for guidelines restricting use of RDF features, while positively correlating for guidelines encouraging external linkage and vocabulary re-use. Finally, we present a summary of conformance for the different guidelines, and present the top-ranked data providers in terms of a combined PageRank and Linked Data conformance score.

[GHKP12] Birte Glimm, Adian Hogan, Markus Krötzsch, and Axel Polleres. OWL: Yet to arrive on the web of data? In WWW2012 Workshop on Linked Data on the Web (LDOW2012), Lyon, France, April 2012. [ .pdf ]
Seven years on from OWL becoming a W3C recommendation, and two years on from the more recent OWL 2 W3C recommendation, OWL has still experienced only patchy uptake on the Web. Although certain OWL features (like owl:sameAs) are very popular, other features of OWL are largely neglected by publishers in the Linked Data world. This may suggest that despite the promise of easy implementations and the proposal of tractable profiles suggested in OWL's second version, there is still no “right” standard fragment for the Linked Data community. In this paper, we (1) analyse uptake of OWL on the Web of Data, (2) gain insights into the OWL fragment that is actually used/usable on the Web, where we arrive at the conclusion that this fragment is likely to be a simplified profile based on OWL RL, (3) propose and discuss such a new fragment, which we call OWL LD (for Linked Data).

[KUHP12] Tobias Käfer, Jürgen Umbrich, Aidan Hogan, and Axel Polleres. Towards a dynamic linked data observatory. In WWW2012 Workshop on Linked Data on the Web (LDOW2012), Lyon, France, April 2012. [ .pdf ]
We describe work-in-progress on the design and methodology of the Dynamic Linked Data Observatory: a framework to monitor Linked Data over an extended period of time. The core goal of our work is to collect frequent, continuous snapshots of a subset of the Web of Data that is interesting for further study and experimentation, with an aim to capture raw data about the dynamics of Linked Data. The resulting corpora will be made openly and continuously available to the Linked Data research community. Herein, we (1) motivate the importance of such a corpus; (2) out- line some of the use-cases and requirements for the resulting snapshots; (3) discuss different “views” of the Web of Data which affect how we define a sample to monitor; (4) detail how we select the scope of the monitoring experiment through sampling, (5) discuss the final design of the monitoring framework which will capture regular snapshots of (subsets of) the Web of Data over the coming months and years.

[UKP+12] Jürgen Umbrich, Marcel Karnstedt, Josiane Xavier Parreira, Axel Polleres, and Manfred Hauswirth. Linked Data and Live Querying for Enabling Support Platforms for Web Dataspaces. In Proceedings of the 3rd International Workshop on Data Engineering Meets the Semantic Web (DESWEB), co-located with ICDE2012, Washington DC, USA, April 2012. [ .pdf ]
Enabling the “Web of Data” has recently gained increased attention, particularly driven by the success of Linked Data. The agreed need for technologies from the database domain is therein often referred to as the “Web as a Database”, a concept that is still more a vision than a reality. Meanwhile, the database community proposed the notion of dataspaces managed by support platforms, as an alternative view on the data management problem for small-scale, loosely connected environments of heterogenous data sources. The Web of Data can actually be seen as a collection of inter-connected dataspaces. In this work, we propose a combination of Linked Data and database technologies to provide support platforms for these Web dataspaces. We argue that while separated, Linked Data still lacks database technology and the dataspace idea lacks openness and scale. We put particular focus on the challenge of how to index, search and query structured data on the Web in a way that is appropriate for its dynamic, heterogeneous, loosely connected, and open character. Based on an empirical study, we argue that none of the two extremes on its own - centralised repositories vs. on-demand distributed querying - can meet all requirements. We propose and discuss an alternative hybrid approach combining the best of both sides to find a better tradeoff between result freshness and fast query response times.

[ZLPS12] Antoine Zimmermann, Nuno Lopes, Axel Polleres, and Umberto Straccia. A general framework for representing, reasoning and querying with annotated semantic web data. Journal of Web Semantics (JWS), 12:72-95, March 2012. [ http ]
We describe a generic framework for representing and reasoning with annotated Semantic Web data, a task becoming more important with the recent increased amount of inconsistent and non-reliable meta-data on the web. We formalise the annotated language, the corresponding deductive system and address the query answering problem. Previous contributions on specific RDF annotation domains are encompassed by our unified reasoning formalism as we show by instantiating it on (i) temporal, (ii) fuzzy, and (iii) provenance annotations. Moreover, we provide a generic method for combining multiple annotation domains allowing to represent, e.g., temporally-annotated fuzzy RDF. Furthermore, we address the development of a query language - AnQL - that is inspired by SPARQL, including several features of SPARQL 1.1 (subqueries, aggregates, assignment, solution modifiers) along with the formal definitions of their semantics.

[BDK+12] Stefan Bischof, Stefan Decker, Thomas Krennwallner, Nuno Lopes, and Axel Polleres. Mapping between RDF and XML with XSPARQL. Journal on Data Semantics, 1(3):147-185, 2012.
One promise of Semantic Web applications is to seamlessly deal with heterogeneous data. The Extensible Markup Language (XML) has become widely adopted as an almost ubiquitous interchange format for data, along with transformation languages like XSLT and XQuery to translate data from one XML format into another. However, the more recent Resource Description Framework (RDF) has become another popular standard for data representation and exchange, supported by its own query language SPARQL, that enables extraction and transformation of RDF data. Being able to work with XML and RDF using a common framework eliminates several unnecessary steps that are currently required when handling both formats side by side. In this paper we present the XSPARQL language that, by combin- ing XQuery and SPARQL, allows to query XML and RDF data using the same framework and transform data from one format into the other. We focus on the semantics of this combined language and present an implementation, including discussion of query optimisations along with benchmark evaluation.

[HZU+12] Aidan Hogan, Antoine Zimmermann, Jürgen Umbrich, Axel Polleres, and Stefan Decker. Scalable and distributed methods for resolving, consolidating, matching and disambiguating entities in linked data corpora. Journal of Web Semantics (JWS), 10:76-110, January 2012.
With respect to large-scale, static, Linked Data corpora, in this paper we discuss scalable and distributed methods for: (i) entity consolidation-identifying entities that signify the same referent, aka. smushing, entity resolution, object consolidation, etc.-using explicit owl:sameAs relations; (ii) extended entity consolidation based on a subset of OWL 2 RL/RDF rules-particularly over inverse-functional properties, functional-properties and (max-)cardinality restrictions with value one; (iii) deriving weighted concurrence measures between entities in the corpus based on shared inlinks/outlinks and attribute values using statistical analyses; (iv) disambiguating (initially) consolidated entities based on inconsistency detection using OWL 2 RL/RDF rules. Our methods are based upon distributed sorts and scans of the corpus, where we purposefully avoid the requirement for indexing all data. Throughout, we offer evaluation over a diverse Linked Data corpus consisting of 1.118 billion quadruples derived from a domain-agnostic, open crawl of 3.985 million RDF/XML Web documents, demonstrating the feasibility of our methods at that scale, and giving insights into the quality of the results for real-world data.


2011


[MAHP11] Alejandro Mallea, Marcelo Arenas, Aidan Hogan, and Axel Polleres. On Blank Nodes. In Proceedings of the 10th International Semantic Web Conference (ISWC 2011), volume 7031 of Lecture Notes in Computer Science (LNCS), Bonn, Germany, October 2011. Springer. Nominated for best paper award. [ .pdf ]
Blank nodes are defined in RDF as `existential variables' in the same way that has been used before in mathematical logic. However, evidence suggests that actual usage of RDF does not follow this definition. In this paper we thoroughly cover the issue of blank nodes, from incomplete information in database theory, over different treatments of blank nodes across the W3C stack of RDF-related standards, to empirical analysis of RDF data publicly available on the Web. We then summarize alternative approaches to the problem, weighing up advantages and disadvantages, also discussing proposals for Skolemization.

[LBP11] Nuno Lopes, Stefan Bischof, and Axel Polleres. On the semantics of heterogeneous querying of relational, XML, and RDF data with XSPARQL. In Proceedings of the 15th Portuguese Conference on Artificial Intelligence (EPIA2011) - Computational Logic with Applications Track, Lisbon, Portugal, October 2011. [ .pdf ]
XSPARQL is a transformation and query language that caters for heterogenous sources: in its present status it is possible to transform data between XML and RDF formats due to the integration of the XQuery and SPARQL query languages. In this paper we propose an extension of the XSPARQL language to incorporate data contained in relational databases by integrating a subset of SQL in the syntax of XSPARQL. Exposing data contained in relational databases as RDF is a necessary step towards the realisation of the Semantic Web and Web of Data. We present the syntax of an extension of the XSPARQL language catering for the inclusion of the SQL query language along with the semantics based on the XQuery formal semantics and sketch how this extended XSPARQL language can be used to expose RDB2RDF mappings, as currently being discussed in the W3C RDB2RDF Working Group.

[HNP+11] Andreas Harth, Barry Norton, Axel Polleres, Brahmananda Sapkota, Sebastian Speiser, Steffen Stadtmüller, and Osma Suominen. RDF needs annotations. In W3C Workshop on Data and Services Integration, Bedford, MA, USA, October 2011. [ .pdf ]
A sizable amount of data on the Web is currently available via Web APIs that expose data in formats such as JSON or XML. Combining data from different APIs and data sources requires glue code which is typically not shared and hence not reused. We derive requirements for a mechanism that brings data and functionality currently available via ad-hoc APIs into a coherent framework. Such standardised access to content and functionality would reduce the effort for data integration and the combination of service functionality, leading to reduced effort in composing data and services from multiple providers.

[DMZ+11] Anca Dumitrache, Alessandra Mileo, Antoine Zimmermann, Axel Polleres, Philipp Obermeier, and Owen Friel. Enabling privacy-preserving semantic presence in instant messaging systems. In 7th International and Interdisciplinary Conference on Modeling and Using Context 2011 (CONTEXT'11), Karlsruhe, Germany, September 2011. [ .pdf ]
In pervasive environments, presence-based application development via Presence Management Systems (PMSs) is a key factor to optimise the management of communication channels, driving productivity increase. Solutions for presence management should satisfy the interoperability requirements, in turn providing context-centric presence analysis and privacy management. In order to push PMSs towards flexible, open and context-aware presence management, we propose some adaptation of two extensions to standard XML-based XMPP for message exchange in online communication systems. The contribution allows for more complex specification and management of nested group and privacy lists, where semantic technologies are used to map all messages into RDF vocabularies and pave the way for a broader semantic integration of heterogeneous and distributed presence information sources in the standard PMSs framework.

[PDA+11] Axel Polleres, Claudia D'Amato, Marcelo Arenas, Siegfried Handschuh, Paula Kroner, Sascha Ossowski, and Peter Patel-Schneider, editors. Reasoning Web. Semantic Technologies for the Web of Data. (ReasoningWeb 2011), volume 6848 of Lecture Notes in Computer Science (LNCS). Springer, Galway, Ireland, August 2011. [ http ]
The Reasoning Web Summer School has become a well-established event in the area of applications of reasoning techniques on the Web both targeting scientific discourse of established researchers and attracting young researchers to this emerging field. After the previous successful editions in Malta (2005), Lisbon (2006), Dresden (2007 and 2010), Venice (2008), and Bressanone-Brixen (2009), this year's edition moved to the west of Ireland, hosted by the Digital Enterprise Research Institute (DERI) at the National University of Ireland, Galway. By co-locating this year's summer school with the 5th International Conference on Web Reasoning and Rule Systems (RR2011) we hope to have further promoted interaction between researchers, practitioners and students. The 2011 school programme focused around the central topic of applications of Reasoning for the emerging “Web of Data”, with twelve exciting lectures.

[HPPR11] Aidan Hogan, Jeff Z. Pan, Axel Polleres, and Yuan Ren. Scalable OWL 2 reasoning for linked data. In Axel Polleres, Claudia D'Amato, Marcelo Arenas, Siegfried Handschuh, Paula Kroner, Sascha Ossowski, and Peter Patel-Schneider, editors, Reasoning Web. Semantic Technologies for the Web of Data. (ReasoningWeb 2011), volume 6848 of Lecture Notes in Computer Science (LNCS), pages 250-325. Springer, Galway, Ireland, August 2011. [ .pdf ]
The goal of the Scalable OWL 2 Reasoning for Linked Data lecture is twofold: first, to introduce scalable reasoning and querying techniques to Semantic Web researchers as powerful tools to make use of Linked Data and large-scale ontologies, and second, to present interesting research problems for the Semantic Web that arise in dealing with TBox and ABox reasoning in OWL 2. The lecture consists of three parts. The first part will begin with an introduction and motivation for reasoning over Linked Data, including a survey of the use of RDFS and OWL on the Web. The second part will present a scalable, distributed reasoning service for instance data, applying a custom subset of OWL 2 RL/RDF rules (based on a tractable fragment of OWL 2). The third part will present recent work on faithful approximate reasoning for OWL 2 DL. The lecture will include our implementation of the mentioned techniques as well as their evaluations. These notes provide complimentary reference material for the lecture, and follow the three-part structure and content of the lecture.

[DTP11] Renaud Delbru, Giovanni Tummarello, and Axel Polleres. Context-dependent OWL reasoning in sindice - experiences and lessons learnt. In Web Reasoning and Rule Systems - Fifth International Conference, RR2011, volume 6902 of Lecture Notes in Computer Science (LNCS), pages 46-60, Galway, Ireland, August 2011. Springer. [ .pdf ]
The Sindice Semantic Web index provides search capabilities over today more than 220 million documents. Reasoning over web data enables to make explicit what would otherwise be implicit knowledge: it adds value to the information and enables Sindice to ultimately be more competitive in terms of precision and recall. However, due to the scale and heterogeneity of web data, a reasoning engine for the Sindice system must (1) scale out through parallelisation over a cluster of machines; and (2) cope with unexpected data usage. In this paper, we report our experiences and lessons learnt in building a large scale reasoning engine for Sindice. The reasoning approach has been deployed, used and improved since 2008 within Sindice and has enabled Sindice to reason over billions of triples. First, we introduce our notion of context-dependent reasoning for RDF entities published on the Web according to the linked data principle. We then illustrate an efficient methodology to perform context-dependent RDFS and partial OWL inference based on a persistent TBox composed of a network of web ontologies. Finally we report performance evaluation results of our implementation underlying the Sindice web data index.

[BLP11] Stefan Bischof, Nuno Lopes, and Axel Polleres. Improve efficiency of mapping data between XML and RDF with XSPARQL. In Web Reasoning and Rule Systems - Fifth International Conference, RR2011, volume 6902 of Lecture Notes in Computer Science (LNCS), pages 232-237, Galway, Ireland, August 2011. Springer. Short paper. [ .pdf ]
XSPARQL is a language to transform data between the tree-based XML format and the graph-based RDF format. XML is a widely adopted data exchange format which brings its own query language XQuery along. RDF is the standard data format of the Semantic Web with SPARQL being the corresponding query language. XSPARQL combines XQuery and SPARQL to a unified query language which provides a more intuitive and maintainable way to translate data between the two data formats. A naive implementation of XSPARQL can be inefficient when evaluating nested queries. However, such queries occur often in practice when dealing with XML data. We present and compare several approaches to optimise nested queries. By implementing these optimisations we improve efficiency up to two orders of magnitude in a practical evaluation.

[SFZ+11] Ratnesh Sahay, Ronan Fox, Antoine Zimmermann, Axel Polleres, and Manfred Hauswrith. A methodological approach for ontologising and aligning health level seven (HL7) applications. In MISI (Massive Information Sharing and Integration) Conference - Special Track on Eletronic Healthcare (SALUS 2011), Vienna, Austria, August 2011. [ .pdf ]
Healthcare applications are complex in the way data and schemas are organised in their internal systems. Widely deployed healthcare standards like Health Level Seven (HL7) V2 are designed using flexible schemas which allow several choices when constructing clinical messages. The recently emerged HL7 V3 has a centrally consistent information model that controls terminologies and concepts shared by V3 applications. V3 information models are arranged in several layers (abstract to concrete layers). V2 and V3 systems raise interoperability challenges: firstly, how to exchange clinical messages between V2 and V3 applications, and secondly, how to integrate globally defined clinical concepts with locally constructed concepts. The use of ontologies for interoperable healthcare applications has been advocated by domain and knowledge representation specialists. This paper addresses two main areas of an ontology-based integration framework: (1) an ontology building methodology for the HL7 standard where ontologies are developed in separated global and local layers; and (2) aligning V2 and V3 ontologies. We propose solutions that: (1) provide a semi-automatic mechanism to build HL7 ontologies; (2) provide a semi-automatic mechanism to align HL7 ontologies and transform underlying clinical messages. The proposed methodology has developed HL7 ontologies of 300 concepts in average for each version. These ontologies and their alignments are deployed and evaluated under a semantically-enabled healthcare integration framework.

[AHP11] Andreas Harth Aidan Hogan and Axel Polleres. Scalable authoritative owl reasoning for the web. In Amit Sheth, editor, Semantic Services, Interoperability and Web Applications: Emerging Concepts, pages 131-177. IGI Global, June 2011. Invited re-publication. [ http ]
In this chapter, the authors discuss the challenges of performing reasoning on large scale RDF datasets from the Web. Using ter-Horst's pD* fragment of OWL as a base, the authors compose a rule-based framework for application to Web data: they argue their decisions using observations of undesirable examples taken directly from the Web. The authors further temper their OWL fragment through consideration of “authoritative sources” which counter-acts an observed behaviour which they term “ontology hijackin”: new ontologies published on the Web re-defining the semantics of existing entities resident in other ontologies. They then present their system for performing rule-based forward-chaining reasoning which they call SAOR: Scalable Authoritative OWL Reasoner. Based upon observed characteristics of Web data and reasoning in general, they design their system to scale: the system is based upon a separation of terminological data from assertional data and comprises of a lightweight in-memory index, on-disk sorts and file-scans. The authors evaluate their methods on a dataset in the order of a hundred million statements collected from real-world Web sources and present scale-up experiments on a dataset in the order of a billion statements collected from the Web. In this republished version, the authors also present extended discussion reflecting upon recent developments in the area of scalable RDFS/OWL reasoning, some of which has drawn inspiration from the original publication (Hogan, et al., 2009).

[Pol11] Axel Polleres. Semantic Web Technologies: From Theory to Practice, March 2011. Kumulative Habilitationsschrift zur Erlangung der Lehrbefugnis im Fach “Informationssysteme”. [ .pdf ]
The Semantic Web is about to grow up. Over the last few years technologies and standards to build up the architecture of this next generation of the Web have matured and are being deployed on large scale in many live Web sites. The underlying technology stack of the Semantic Web consists of several standards endorsed by the World Wide Web consortium (W3C) that provide the formal underpinings of a machine-readable “Web of Data”: (i) the eXtensible Markup Language (XML) as a uniform exchange syntax; (ii) the Resource Description Framework (RDF) as a uniform data exchange format; (iii) RDF Schema and the Web Ontology Language (OWL) for describig ontologies; (iv) the Rule Interchange Format (RIF) to exchange rules; (v) XQuery and SPARQL as query and transformation languages. The present habilitation thesis comprises a collection of articles reflecting the author's contribution in addressing a number of relevant research problems to close gaps in the Semantic Web architecture regarding the theoretical and practical interplay of these standards.

[FMPGP11] Javier D. Fernández, Miguel A. Martínez-Prieto, Claudio Gutierrez, and Axel Polleres. Binary RDF Representation for Publication and Exchange (HDT), March 2011. W3C member submission. [ http ]
RDF HDT (Header-Dictionary-Triples) is a binary format for publishing and exchanging RDF data at large scale. RDF HDT represents RDF in a compact manner, natively supporting splitting huge RDF graphs into several chunks. It is designed to allow high compression rates. This is achieved by organizing and representing the RDF graph in terms of two main components: Dictionary and Triples structure. The Dictionary organizes all vocabulary present in the RDF graph in a manner that permits rapid search and high levels of compression. The Triples component comprises the pure structure of the underlying graph in a compressed form. An additional and RECOMMENDED Header component includes extensible metadata describing the RDF data set and its organization. Further, the document specifies how to efficiently translate between HDT and other RDF representation formats, such as Notation 3.

[HHU+11] Aidan Hogan, Andreas Harth, Jürgen Umbrich, Sheila Kinsella, Axel Polleres, and Stefan Decker. Searching and browsing linked data with SWSE: The semantic web search engine. Journal of Web Semantics (JWS), 9(4):365-401, 2011. [ http ]
In this paper, we discuss the architecture and implementation of the Semantic Web Search Engine (SWSE). Following traditional search engine architecture, SWSE consists of crawling, data enhancing, indexing and a user interface for search, browsing and retrieval of information; unlike traditional search engines, SWSE operates over RDF Web data - loosely also known as Linked Data - which implies unique challenges for the system design, architecture, algorithms, implementation and user interface. In particular, many challenges exist in adopting Semantic Web technologies for Web data: the unique challenges of the Web - in terms of scale, unreliability, inconsistency and noise - are largely overlooked by the current Semantic Web standards. Herein, we describe the current SWSE system, initially detailing the architecture and later elaborating upon the function, design, implementation and performance of each individual component. In so doing, we also give an insight into how current Semantic Web standards can be tailored, in a best-effort manner, for use on Web data. Throughout, we offer evaluation and complementary argumentation to support our design choices, and also offer discussion on future directions and open research questions. Later, we also provide candid discussion relating to the difficulties currently faced in bringing such a search engine into the mainstream, and lessons learnt from roughly six years working on the Semantic Web Search Engine project.

[HBPS11] Aidan Hogan, Piero Bonatti, Axel Polleres, and Luigi Sauro. Robust and scalable linked data reasoning incorporating provenance and trust annotations. Journal of Web Semantics (JWS), 9(2):165-201, 2011. [ .pdf ]
In this paper, we leverage annotated logic programs for tracking indicators of provenance and trust during reasoning, specifically focussing on the use-case of applying a scalable subset of OWL 2 RL/RDF rules over static corpora of arbitrary Linked Data (Web data). Our annotations encode three facets of information: (i) blacklist: a (possibly manually generated) boolean annotation which indicates that the referent data are known to be harmful and should be ignored during reasoning; (ii) ranking: a numeric value derived by a PageRank-inspired technique-adapted for Linked Data-which determines the centrality of certain data artefacts (such as RDF documents and statements); (iii) authority: a boolean value which uses Linked Data principles to conservatively determine whether or not some terminological information can be trusted. We formalise a logical framework which annotates inferences with the strength of derivation along these dimensions of trust and provenance; we formally demonstrate some desirable properties of the deployment of annotated logic programming in our setting, which guarantees (i) a unique minimal model (least fixpoint); (ii) monotonicity; (iii) finitariness; and (iv) finally decidability. In so doing, we also give some formal results which reveal strategies for scalable and efficient implementation of various reasoning tasks one might consider. Thereafter, we discuss scalable and distributed implementation strategies for applying our ranking and reasoning methods over a cluster of commodity hardware; throughout, we provide evaluation of our methods over 1 billion Linked Data quadruples crawled from approximately 4 million individual Web documents, empirically demonstrating the scalability of our approach, and how our annotation values help ensure a more robust form of reasoning. We finally sketch, discuss and evaluate a use-case for a simple repair of inconsistencies detectable within OWL 2 RL/RDF constraint rules using ranking annotations to detect and defeat the “marginal view”, and in so doing, infer an empirical “consistency threshold” for the Web of Data in our setting.

[UHK+11] Jürgen Umbrich, Katja Hose, Marcel Karnstedt, Andreas Harth, and Axel Polleres. Comparing data summaries for processing live queries over linked data. World Wide Web Journal, 14(5-6):495-544, 2011. [ http ]
A growing amount of Linked Data - graph-structured data accessible at sources distributed across the Web - enables advanced data integration and decision-making applications. Typical systems operating on Linked Data collect (crawl) and pre-process (index) large amounts of data, and evaluate queries against a centralised repository. Given that crawling and indexing are time-consuming operations, the data in the centralised index may be out of date at query execution time. An ideal query answering system for querying Linked Data live should return current answers in a reasonable amount of time, even on corpora as large as the Web. In such a live query system source selection - determining which sources contribute answers to a query - is a crucial step. In this article we propose to use lightweight data summaries for determining relevant sources during query evaluation. We compare several data structures and hash functions with respect to their suitability for building such summaries, stressing benefits for queries that contain joins and require ranking of results and sources. We elaborate on join variants, join ordering and ranking. We analyse the different approaches theoretically and provide results of an extensive experimental evaluation.

[dBEPT11] Jos de Bruijn, Thomas Eiter, Axel Polleres, and Hans Tompits. Embedding non-ground logic programs into autoepistemic logic for knowledge base combination. ACM Transactions on Computational Logic, 12(3), 2011. [ .pdf ]
In the context of the Semantic Web, several approaches to the combination of ontologies, given in terms of theories of classical first-order logic and rule bases, have been proposed. They either cast rules into classical logic or limit the interaction between rules and ontologies. Autoepistemic logic (AEL) is an attractive formalism which allows to overcome these limitations, by serving as a uniform host language to embed ontologies and nonmonotonic logic programs into it. For the latter, so far only the propositional setting has been considered. In this paper, we present three embeddings of normal and three embeddings of disjunctive non-ground logic programs under the stable model semantics into first-order AEL. While the embeddings all correspond with respect to objective ground atoms, differences arise when considering non-atomic formulas and combinations with first-order theories. We compare the embeddings with respect to stable expansions and autoepistemic consequences, considering the embeddings by themselves, as well as combinations with classical theories. Our results reveal differences and correspondences of the embeddings and provide useful guidance in the choice of a particular embedding for knowledge combination.


2010


[PC10] Axel Polleres and Huajun Chen, editors. Proceedings of the ISWC 2010 Posters & Demonstrations Track: Collected Abstracts, volume 658 of CEUR Workshop Proceedings, Shanghai, China, November 2010. CEUR-WS.org. [ http ]
The posters and demonstrations track of ISWC 2010 continues the established tradition of providing an interaction and connection opportunity for researchers and practitioners to present and demonstrate their new and innovative work-in-progress. The track gives conference attendees a way to learn about novel on-going research projects that might not yet be complete, but whose preliminary results are already interesting. The track also provides presenters with an excellent opportunity to obtain feedback from their peers in an informal setting from knowledgeable sources. New in this year, we also encouraged authors of accepted full research or in-use papers to present a practical demonstration or poster with additional results.

[LPSZ10] Nuno Lopes, Axel Polleres, Umberto Straccia, and Antoine Zimmermann. AnQL: SPARQLing up annotated RDFS. In Proceedings of the 9th International Semantic Web Conference (ISWC 2010), volume 6496 of Lecture Notes in Computer Science (LNCS), Shanghai, China, November 2010. Springer. [ .pdf ]
Starting from the general framework for Annotated RDFS which we presented in previous work (extending Udrea et al.'s Annotated RDF), we address the development of a query language - AnQL - that is inspired by SPARQL, including several features of SPARQL 1.1. As a side effect we propose formal definitions of the semantics of these features (subqueries, aggregates, assignment, solution modifiers) which could serve as a basis for the ongoing work in SPARQL 1.1. We demonstrate the value of such a framework by comparing our approach to previously proposed extensions of SPARQL and show that AnQL generalises and extends them.

[HPPD10] Aidan Hogan, Jeff Z. Pan, Axel Polleres, and Stefan Decker. SAOR: Template rule optimisations for distributed reasoning over 1 billion linked data triples. In Proceedings of the 9th International Semantic Web Conference (ISWC 2010), volume 6496 of Lecture Notes in Computer Science (LNCS), Shanghai, China, November 2010. Springer. [ .pdf ]
In this paper, we discuss generic optimisations of rule-based materialisation approaches for reasoning over large static RDF datasets. We generalise and re-formalise what we call the "partial-indexing" approach to scalable rule-based materialisation: the approach is based on a separation of terminological data, which has been shown in previous and related works to enable highly scalable and distributable reasoning for specific rulesets; in so doing, we provide some completeness propositions with respect to semi-naive evaluation. We then show how related work on template rules - T-Box-specific dynamic rulesets created by binding the terminological patterns in the static ruleset - can be incorporated in the partial-indexing approach, and optimisations that are possible thereafter. We demonstrate our methods using LUBM(10) for RDFS, pD* (OWL Horst) and OWL 2 RL, and thereafter demonstrate pragmatic distributed reasoning over 1.12b Linked Data triples for a subset of OWL 2 RL we argue to be suitable for the Web use-case.

[HEF+10] Manfred Hauswirth, Jérôme Euzenat, Owen Friel, Keith Griffin, Pat Hession, Brendan Jennings, Tudor Groza, Siegfried Handschuh, Ivana Podnar Zarko, Axel Polleres, and Antoine Zimmermann. Towards consolidated presence. In The 6th International Conference on Collaborative Computing: Networking, Applications and Worksharing (CollaborateCom 2010), Chicago, Illinois, USA, October 2010. IEEE Computer Society. Invited paper. [ .pdf ]
Presence management, i.e., the ability to automatically identify the status and availability of communication partners, is becoming an invaluable tool for collaboration in enterprise contexts. In this paper, we argue for efficient presence management by means of a holistic view of both physical context and virtual presence in online communication channels. We sketch the components for enabling presence as a service integrating both online information as well as physical sensors, discussing benefits, possible applications on top, and challenges of establishing such a service.

[PPSW10b] Reinhard Pichler, Axel Polleres, Sebastian Skritek, and Stefan Woltran. Redundancy elimination on RDF graphs in the presence of rules, constraints, and queries. In Pascal Hitzler and Thomas Lukasiewicz, editors, Web Reasoning and Rule Systems - Fourth International Conference, RR2010, volume 6333 of Lecture Notes in Computer Science (LNCS), pages 133-148, Bressanone, Italy, September 2010. Springer. Best paper award, technical report version available at http://www.deri.ie/fileadmin/documents/DERI-TR-2010-04-23.pdf. [ .pdf ]
Based on practical observations on rule-based inference on RDF data, we study the problem of redundancy elimination on RDF graphs in the presence of rules (in the form of Datalog rules) and con- straints, (in the form of so-called tuple-generating dependencies), and with respect to queries (ranging from conjunctive queries up to more complex ones, particularly covering features of SPARQL, such as union, negation, or filters). To this end, we investigate the influence of several problem parameters (like restrictions on the size of the rules, the con- straints, and/or the queries) on the complexity of detecting redundancy. The main result of this paper is a fine-grained complexity analysis of both graph and rule minimisation in various settings.

[Pol10b] Axel Polleres. SPARQL1.1: new features and friends (OWL2, RIF). In Pascal Hitzler and Thomas Lukasiewicz, editors, Web Reasoning and Rule Systems - Fourth International Conference, RR2010, volume 6333 of Lecture Notes in Computer Science (LNCS), pages 23-26, Bressanone, Italy, September 2010. Springer. Slides available at http://www.polleres.net/RR2010_SPARQL11_Tutorial/. [ http ]
In this tutorial we will give an overview of new features in SPARQL 1.1, which the W3C is currently working on, as well as on the interplay with its ”neighbour standards”, OWL2 and RIF. We will also give a rough overview of existing implementations to play around with.

[OMP10] Philipp Obermeier, Marco Marano, and Axel Polleres. Processing RIF and OWL2RL within DLVHEX. In Pascal Hitzler and Thomas Lukasiewicz, editors, Web Reasoning and Rule Systems - Fourth International Conference, RR 2010, volume 6333 of Lecture Notes in Computer Science (LNCS), pages 244-250, Bressanone, Italy, September 2010. Springer. Demo Paper. [ .pdf ]
We present an extension of the DLVHEX system to support RIF-Core, a dialect of W3C's Rule Interchange Format (RIF), as well as combinations of RIF-Core and OWL2RL ontologies. DLVHEX is a plugin system on top of DLV, a disjunctive Datalog engine which enables higher-order and external atoms, as well as input rewriting capabilities, which are provided as plugins and enable DLVHEX to bidirectionally exchange data with external knowledge bases and consuming input in different Semantic Web languages. In fact, there already exist plugins for languages such as RDF and SPARQL. Our new plugin facilitates consumption and processing of RIF rulesets, as well as OWL2RL reasoning by a 2-step-reduction to DVLHEX via embedding in RIF-Core. The current version implements the translation from OWL2RL to RIF by a static rule set and supports the RIF built-ins mandatory for this reduction trough external atoms in DLVHEX. For the future we plan to switch to a dynamic approach for RIF embedding of OWL2RL and extend the RIF reasoning capabilities to more features of RIF-BLD. We provide a description of our current system, its current development status as well as an illustrative example, and conclude future plans to complete the Semantic Web library of plugins for DLVHEX.

[Pol10a] Axel Polleres. Semantic web technologies: From theory to standards. In 21st National Conference on Artificial Intelligence and Cognitive Science (AICS2010), Galway, Ireland, August 2010. Review paper (appeared in the informal conference proceedings). [ .pdf ]
This paper summarises the evolution of W3C standards in the area of Semantic Web technologies, as well as gaps within these standards still to be filled in terms of standardisation. Moreover, we give a subjective survey of the most influential scientific works which have contributed to the development of these standards and to closing the gaps between them. The Semantic Web proves to become an interesting application field for Artificial Intelligence; we aim here at both giving an overview of own work in the area as well as providing an entry point for researchers interested in the foundations of Semantic Web standards and technologies.

[SLLP10] Umberto Straccia, Nuno Lopes, Gergely Lukácsy, and Axel Polleres. A general framework for representing and reasoning with annotated semantic web data. In Proceedings of the 24th AAAI Conference on Artificial Intelligence (AAAI 2010), Special Track on Artificial Intelligence and the Web, Atlanta, Georgia, USA, July 2010. [ .pdf ]
We describe a generic framework for representing and reasoning with annotated Semantic Web data, a task becoming more important with the recent increased amount of inconsistent and non- reliable meta-data on the web. We formalise the annotated language, the corresponding deductive system and address the query answering problem. Our work extends previous contributions on RDF annotations by providing a unified reasoning formalism and allowing the seamless combination of different annotation domains. We show that current RDF stores can easily be extended to our framework. We demonstrate the feasibility of our method by instantiating it on (i) temporal RDF; (ii) fuzzy RDF; (iii) and their combination. A prototype shows that implementing and combining new domains is easy.

[LZH+10] Nuno Lopes, Antoine Zimmermann, Aidan Hogan, Gergely Lukácsy, Axel Polleres, Umberto Straccia, and Stefan Decker. RDF needs annotations. In W3C Workshop on RDF Next Steps, Stanford, Palo Alto, CA, USA, June 2010. [ http ]
While the current mechanism of reification in RDF is without semantics and widely considered inappropriate and cumbersome, some form of reification - speaking about triples themselves - is needed in RDF for many reasonable applications: in particular, reification allows for enhancing triples with annotations relating to provenance, spatio-temporal validity, degrees of trust, fuzzy values and/or other contextual information. In this position paper, we argue that - besides resolving the issue of how to syntactically represent reification in the future (i.e., whether to stick with the current reification mechanism or standardise a different mechanism such as Named Graphs) - it is time to agree on certain core annotations that are widely needed. We summarise existing work and provide a possible direction towards handling reification by means of a general annotation framework that can be instantiated for those major use cases we currently see arising.

[LBE+10] Nuno Lopes, Stefan Bischof, Orri Erling, Axel Polleres, Alexandre Passant, Diego Berrueta, Antonio Campos, Jérôme Euzenat, Kingsley Idehen, Stefan Decker, Stéphane Corlosquet, Jacek Kopecký, Janne Saarela, Thomas Krennwallner, Davide Palmisano, and Michal Zaremba. RDF and XML: Towards a unified query layer. In W3C Workshop on RDF Next Steps, Stanford, Palo Alto, CA, USA, June 2010. [ http ]
One of the requirements of current Semantic Web applications is to deal with heterogeneous data. The Resource Description Framework (RDF) is the W3C recommended standard for data representation, yet data represented and stored using the Extensible Markup Language (XML) is almost ubiquitous and remains the standard for data exchange. While RDF has a standard XML representation, XML Query languages are of limited use for transformations between natively stored RDF data and XML. Being able to work with both XML and RDF data using a common framework would be a great advantage and eliminate unnecessary intermediate steps that are currently used when handling both formats.

[VRL+10] María-Esther Vidal, Edna Ruckhaus, Tomas Lampo, Amadís Marínez, Javier Sierra, and Axel Polleres. On the efficiency of joining group patterns in SPARQL queries. In Proceedings of the 7th European Semantic Web Conference (ESWC2010), Heraklion, Greece, May 2010. Springer. [ .pdf ]
In SPARQL queries, the combination of triple patterns is expressed by using shared variables across patterns. Based on this characterization, basic graph patterns in a SPARQL query can be partitioned into groups of acyclic pattern combinations that share exactly one variable, or star-shaped groups. We observe that the number of triples in a group is proportional to the number of individuals that play the role of the subject or the object; however, depending on the degree of participation of the subject individuals in the properties, a group could be not much larger than a class or type to which the subject or object belongs. Thus, it may be significantly more efficient to independently evaluate each of the groups, and then merge the resulting sets, than linearly joining all triples in a basic graph pattern. Based on these properties of star-shaped groups, we have developed query optimization and evaluation techniques. We have conducted an empirical analysis on the benefits of the optimization and evaluation techniques in several SPARQL query engines. We observe that our proposed techniques are able to speed up query evaluation time for join queries with star-shaped patterns by at least one order of magnitude.

[PPH10] Jeff Z. Pan, Axel Polleres, and Aidan Hogan. Scalable owl reasoning for linked data, May 2010. Slides available at http://www.abdn.ac.uk/~csc280/tutorial/eswc2010/. [ http ]
Tutorial at the 7th Extended Semantic Web Conference (ESWC2010)

[HPUZ10] Aidan Hogan, Axel Polleres, Jürgen Umbrich, and Antoine Zimmermann. Some entities are more equal than others: statistical methods to consolidate linked data. In Workshop on New Forms of Reasoning for the Semantic Web: Scalable & Dynamic (NeFoRS10), Heraklion, Greece, May 2010. [ .pdf ]
We propose a method for consolidating entities in RDF data on the Web. Our approach is based on a statistical analysis of the use of predicates and their associated values to identify “quasi”-key properties. Compared to a purely symbolic based approach, we obtain promising results, retrieving more identical entities with a high precision. We also argue that our technique scales well - possibly to the size of the current Web of Data - as opposed to more expensive existing approaches.

[KOPP10] Philipp Kärger, Daniel Olmedilla, Alexandre Passant, and Axel Polleres, editors. Proceedings of the Second Workshop on Trust and Privacy on the Social and Semantic Web (SPOT2010), volume 576 of CEUR Workshop Proceedings, Heraklion, Greece, May 2010. CEUR-WS.org. [ http ]
Workshop Proceedings. This workshop was co-located with ESWC 2010.

[PPSW10a] Reinhard Pichler, Axel Polleres, Sebastian Skritek, and Stefan Woltran. Minimising rdf graphs under rules and constraints revisited. In 4th Alberto Mendelzon Workshop on Foundations of Data Management, volume 494 of CEUR Workshop Proceedings. CEUR-WS.org, May 2010. [ .pdf ]
Based on practical observations on rule-based inference on RDF data, we study the problem of redundancy elimination in RDF in the presence of rules (in the form of Datalog rules) and constraints (in the form of so-called tuple-generating dependencies). To this end, we investigate the influence of several problem parameters (like restrictions on the size of the rules and/or the constraints) on the complexity of detecting redundancy. The main result of this paper is a fine-grained complexity analysis of both graph and rule minimisation in various settings.

[HHP+10] Aidan Hogan, Andreas Harth, Alexandre Passant, Stefan Decker, and Axel Polleres. Weaving the pedantic web. In 3rd International Workshop on Linked Data on the Web (LDOW2010) at WWW2010, Raleigh, USA, April 2010. [ .pdf ]
Over a decade after RDF has been published as a W3C recommendation, publishing open and machine-readable content on the Web has recently received a lot more attention, including from corporate and governmental bodies; notably thanks to the Linked Open Data community, there now exists a rich vein of heterogeneous RDF data published on the Web (the so-called “Web of Data”) accessible to all. However, RDF publishers are prone to making errors which compromise the effectiveness of applications leveraging the resulting data. In this paper, we discuss common errors in RDF publishing, their consequences for applications, along with possible publisher-oriented approaches to improve the quality of structured, machine-readable and open data on the Web.

[UHH+10] Jürgen Umbrich, Michael Hausenblas, Aidan Hogan, Axel Polleres, and Stefan Decker. Towards dataset dynamics: Change frequency of linked open data sources. In 3rd International Workshop on Linked Data on the Web (LDOW2010) at WWW2010, Raleigh, USA, April 2010. [ .pdf ]
Datasets in the LOD cloud are far from being static in their nature and how they are exposed. As resources are added and new links are set, applications consuming the data should be able to deal with these changes. In this paper we investigate how LOD datasets change and what sensible measures there are to accommodate dataset dynamics. We compare our findings with traditional, document-centric studies concerning the “freshness” of the document collections and propose metrics for LOD datasets.

[HHK+10] Andreas Harth, Katja Hose, Marcel Karnstedt, Axel Polleres, Kai-Uwe Sattler, and Jürgen Umbrich. Data summaries for on-demand queries over linked data. In Proceedings of the 19th World Wide Web Conference (WWW2010), Raleigh, NC, USA, April 2010. Technical report version available at http://www.deri.ie/fileadmin/documents/DERI-TR-2009-11-17.pdf. [ .pdf ]
Typical approaches for search and querying over structured Web Data collect (crawl) and pre-process (index) large amounts of data before allowing for query answering in a central data warehouse. This time-consuming pre-processing phase decreases the freshness of query results and only uses to a limited degree the benefits of Linked Data where structured data is accessible live and up-to-date at distributed Web resources that may change constantly. An ideal query answering system for Linked Data should return always current answers in a reasonable amount of time, even on corpora as large as the web. Query processors evaluating queries directly on the life sources require knowledge of the contents of data sources. In the current paper we develop and evaluate a probabilistic index structure for covering graph-structured content of sources adhering to Linked Data principles, provide an algorithm for answering conjunctive queries over Linked Data on the web exploiting this structure, and evaluate the system using synthetically generated queries. We find that our lightweight index structure enable more complete query results over Linked Data compared to direct lookup approaches, while keeping the overhead for additional lookups and index maintenance low.

[PHHD10] Axel Polleres, Aidan Hogan, Andreas Harth, and Stefan Decker. Can we ever catch up with the web? Semantic Web - Interoperability, Usability, Applicability, 1(1-2):45-52, 2010. [ .pdf ]
The Semantic Web is about to grow up. By efforts such as the Linking Open Data initiative, we finally find ourselves at the edge of a Web of Data becoming reality. Standards such as OWL 2, RIF and SPARQL 1.1 shall allow us to reason with and ask complex structured queries on this data, but still they do not play together smoothly and robustly enough to cope with huge amounts of noisy Web data. In this paper, we discuss open challenges relating to querying and reasoning with Web data and raise the question: can the burgeoning Web of Data ever catch up with the now ubiquitous HTML Web?

[PAV+10] Julian Padget, Alexander Artikis, Wamberto Vasconcelos, Kostas Stathis, Viviane Torres da Silva, Eric Matson, and Axel Polleres, editors. Coordination, Organizations, Institutions, and Norms in Agent Systems V, volume 6069 of Lecture Notes in AI (LNAI). Springer, 2010.
COIN 2009 International Workshops: COIN@AAMAS 2009 Budapest, Hungary, May 2009, COIN@IJCAI 2009, Pasadena, USA, July 2009, COIN@MALLOW 2009,Turin, Italy, September 2009, Revised Selected Papers. This book constitutes the thoroughly refereed post-workshop proceedings of the International Workshop on Coordination, Organization, Institutions and Norms in Agent Systems, COIN 2009.

[dBPPV10] Jos de Bruijn, David Pearce, Axel Polleres, and Agustín Valverde. A semantical framework for hybrid knowledge bases. Knowledge and Information Systems (KAIS), 25(1):81-104, 2010. [ .pdf ]
In the ongoing discussion about combining rules and Ontologies on the Semantic Web a recurring issue is how to combine first-order classical logic with nonmonotonic rule languages. Whereas several modular approaches to define a combined semantics for such hybrid knowledge bases focus mainly on decidability issues, we tackle the matter from a more general point of view. In this paper we show how Quantified Equilibrium Logic (QEL) can function as a unified framework which embraces classical logic as well as disjunctive logic programs under the (open) answer set semantics. In the proposed variant of QEL we relax the unique names assumption, which was present in earlier versions of QEL. Moreover, we show that this framework elegantly captures the existing modular approaches for hybrid knowledge bases in a unified way.


2009


[ZSFP09] Antoine Zimmermann, Ratnesh Sahay, Ronan Fox, and Axel Polleres. Heterogeneity and context in semantic-web-enabled HCLS systems. In Robert Meersman, Tharam S. Dillon, and Pilar Herrero, editors, OTM 2009, Part II: Proceedings of the 8th International Conference on Ontologies, DataBases, and Applications of Semantics (ODBASE 2009), volume 5871 of Lecture Notes in Computer Science (LNCS), pages 1165-1182, Vilamoura, Algarve, Portugal, November 2009. Springer. [ .pdf ]
The need for semantics preserving integration of complex data has been widely recognized in the healthcare domain. While standards such as Health Level Seven (HL7) have been developed in this direction, they have mostly been applied in limited, controlled environments, still being used incoherently across countries, organizations, or hospitals. In a more mobile and global society, data and knowledge are going to be commonly exchanged between various systems at Web scale. Specialists in this domain have increasingly argued in favor of using Semantic Web technologies for modeling healthcare data in a well formalized way. This paper provides a reality check in how far current Semantic Web standards can tackle interoperability issues arising in such systems driven by the modeling of concrete use cases on exchanging clinical data and practices. Recognizing the insufficiency of standard OWL to model our scenario, we survey theoretical approaches to extend OWL by modularity and context towards handling heterogeneity in Semantic-Web-enabled health care and life sciences (HCLS) systems. We come to the conclusion that none of these approaches addresses all of our use case heterogeneity aspects in its entirety. We finally sketch paths on how better approaches could be devised by combining several existing techniques.

[PS09] Axel Polleres and Terrance Swift, editors. Web Reasoning and Rule Systems - Third International Conference, RR2009, volume 5837 of Lecture Notes in Computer Science (LNCS), Chantilly, VA, USA, October 2009. Springer. [ http ]
This book constitutes the refereed proceedings of the Third International Conference on Web Reasoning and Rule Systems, RR 2009, held in Chantilly, VA, USA, in October 2009. The 15 revised full papers presented together with 3 invited papers were carefully reviewed and selected from 41 submissions. The papers address all current topics in Web reasoning and rule systems such as proof/deduction procedures, scalability, uncertainty, knowledge amalgamation and querying, and rules for decision support and production systems.

[IKMP09a] Giovambattista Ianni, Thomas Krennwallner, Alessandra Martello, and Axel Polleres. Dynamic querying of mass-storage rdf data with rule-based entailment regimes. In Abraham Bernstein, David R. Karger, Tom Heath, Lee Feigenbaum, Diana Maynard, Enrico Motta, and Krishnaprasad Thirunarayan, editors, Proceedings of the 8th International Semantic Web Conference (ISWC 2009), volume 5823 of Lecture Notes in Computer Science (LNCS), pages 310-327, Washington DC, USA, October 2009. Springer. [ .pdf ]
RDF Schema (RDFS) as a lightweight ontology language is gaining popularity and, consequently, tools for scalable RDFS inference and querying are needed. SPARQL has become recently a W3C standard for querying RDF data, but it mostly provides means for querying simple RDF graphs only, whereas querying with respect to RDFS or other entailment regimes is left outside the current specification. In this paper, we show that SPARQL faces certain unwanted ramifications when querying ontologies in conjunction with RDF datasets that comprise multiple named graphs, and we provide an extension for SPARQL that remedies these effects. Moreover, since RDFS inference has a close relationship with logic rules, we generalize our approach to select a custom ruleset for specifying inferences to be taken into account in a SPARQL query. We show that our extensions are technically feasible by providing benchmark results for RDFS querying in our prototype system , which uses Datalog coupled with a persistent Relational Database as a back-end for implementing SPARQL with dynamic rule-based inference. By employing different optimization techniques like magic set rewriting our system remains competitive with state-of-the-art RDFS querying systems.

[CDC+09] Stéphane Corlosquet, Renaud Delbru, Tim Clark, Axel Polleres, and Stefan Decker. Produce and consume linked data with drupal! In Abraham Bernstein, David R. Karger, Tom Heath, Lee Feigenbaum, Diana Maynard, Enrico Motta, and Krishnaprasad Thirunarayan, editors, Proceedings of the 8th International Semantic Web Conference (ISWC 2009), volume 5823 of Lecture Notes in Computer Science (LNCS), pages 763-778, Washington DC, USA, October 2009. Springer. Best paper award In-Use track. [ .pdf ]
Currently a large number of Web sites are driven by Content Management Systems (CMS) which manage textual and multimedia content but also - inherently - carry valuable information about a site's structure and content model. Exposing this structured information to the Web of Data has so far required considerable expertise in RDF and OWL modelling and additional programming effort. In this paper we tackle one of the most popular CMS: Drupal. We enable site administrators to export their site content model and data to the Web of Data without requiring extensive knowledge on Semantic Web technologies. Our modules create RDFa annotations and - optionally - a SPARQL endpoint for any Drupal site out of the box. Likewise, we add the means to map the site data to existing ontologies on the Web with a search interface to find commonly used ontology terms. We also allow a Drupal site administrator to include existing RDF data from remote SPARQL endpoints on the Web in the site. When brought together, these features allow networked RDF Drupal sites that reuse and enrich Linked Data. We finally discuss the adoption of our modules and report on a use case in the biomedical field and the current status of its deployment.

[BBB+09] Matteo Baldoni, Cristina Baroglio, Jamal Bentahar, Guido Boella, Massimo Cossentino, Mehdi Dastani, Barbara Dunin-Keplicz, Giancarlo Fortino, Marie-Peirre Gleizes, João Leite, Viviana Mascardi, Julian Padget, Juan Pavón, Axel Polleres, Amal El Fallah Seghrouchni, Paolo Torroni, and Rineke Verbrugge, editors. Proceedings of the Second Multi-Agent Logics, Languages, and Organisations Federated Workshops (MALLOW'009), volume 494 of CEUR Workshop Proceedings, Torino, Italy, September 2009. CEUR-WS.org. [ http ]
The Multi-Agent Logics, Languages, and Organisations Federated Workshops (MALLOW for short), in its second edition this year after the success of MALLOW'007 held in Durham (UK), is a forum for researchers interested in sharing their experiences in agents and multi-agent systems. MALLOW'009 was held at the Educatorio della Provvidenza, in Torino (Italy), from September 7th, 2009 through September 10th, 2009. This volume contains the proceedings of the five workshops, for a total of forty-seven high quality papers, which were selected by the programme committees of the workshops for presentation. Each workshop has an introductory essay, authored by the organizers, which presents the workshop.

[HKO+09] Michael Hausenblas, Philipp Kärger, Daniel Olmedilla, Alexandre Passant, and Axel Polleres, editors. Proceedings of the First Workshop on Trust and Privacy on the Social and Semantic Web (SPOT2009), volume 447 of CEUR Workshop Proceedings, Heraklion, Greece, June 2009. CEUR-WS.org. [ http ]
Workshop Proceedings. This workshop was co-located with ESWC 2009.

[CCPD09] Stéphane Corlosquet, Richard Cyganiak, Axel Polleres, and Stefan Decker. Rdfa in drupal: Bringing cheese to the web of data. In 5th Workshop on Scripting and Development for the Semantic Web, Heraklion, Greece, May 2009. [ .pdf ]
A large number of web sites are driven by content management systems (CMS), which manage not only textual content but also structured data related to the site's topic. Exposing this information to the Web of Data has so far required considerable expertise in RDF modelling and programming. We present a plugin for the popular CMS Drupal that enables high-quality RDF output with minimal effort from site administrators. This has the potential of greatly increasing the amount and topical range of information available on the Web of Data.

[IKMP09b] Giovambattista Ianni, Thomas Krennwallner, Alessandra Martello, and Axel Polleres. A rule system for querying persistent rdfs data. In Proceedings of the 6th European Semantic Web Conference (ESWC2009), Heraklion, Greece, May 2009. Springer. Demo Paper. [ .pdf ]
In this demo we present GiaBATA, a system for storing, aggregating, and querying Semantic Web data, based on declarative logic programming technology, namely on the dlvhex system, which allows us to implement a fully SPARQL compliant semantics, and on DLVDB , which extends the DLV system with persistent storage capabilities. Compared with off-the-shelf RDF stores and SPARQL engines, we offer more flexible support for rule-based RDFS and other higher entailment regimes by enabling custom reasoning via rules, and the possibility to choose the reference ontology on a per query basis. Due to the declarative approach, GiaBATA gains the possibility to apply well-known logic-level optimization features of logic programming (LP) and deductive database systems. Moreover, our architecture allows for extensions of SPARQL by non-standard features such as aggregates, custom built-ins, or arbitrary rulesets. With the resulting system we provide a flexible toolbox that embeds Semantic Web data and ontologies in a fully declarative LP environment.

[PPT+09] Danh Le Phuoc, Axel Polleres, Giovanni Tummarello, Christian Morbidoni, and Manfred Hauswirth. Rapid semantic web mashup development through semantic web pipes. In Proceedings of the 18th World Wide Web Conference (WWW2009), pages 581-590, Madrid, Spain, April 2009. ACM Press. [ .pdf ]
The use of RDF data published on the Web for applications is still a cumbersome and resource-intensive task due to the limited software support and the lack of standard programming paradigms to deal with everyday problems such as combination of RDF data from different sources, object identifier consolidation, ontology alignment and mediation or plain querying and processing tasks. While in a lot of other areas such tasks are supported by excellent libraries and component-oriented toolboxes of basic processing functionalities, RDF-based Web applications are still largely customized programs for a specific purpose, with little potential for reuse. This increases development costs and incurs a more error-prone development process. Speaking in software engineering terms, this means that a good standard architectural style with good support for rapid application development is still missing. In this paper we present a framework based on the classical abstraction of pipes which tries to remedy this problem and support the fast implementation of software, while preserving desirable properties such as abstraction, encapsulation, component-orientation, code re-usability and maintainability, which are common and well supported in other application areas.

[PH09] Axel Polleres and David Huynh, editors. Journal of Web Semantics, Special Issue: The Web of Data, volume 7(3). Elsevier, 2009.
[PKH+09] Alexandre Passant, Philipp Kärger, Michael Hausenblas, Daniel Olmedilla, Axel Polleres, and Stefan Decker. Enabling trust and privacy on the social web. In W3C Workshop on the Future of Social Networking, Barcelona, Spain, January 2009. [ .html ]
Based on our recent observations at the 7th International Semantic Web Conference and some related workshops as the “Social Data on The Web”, as well as other frequent discussion threads on the Web, trust and privacy on the Social Web remains a hot, yet unresolved topic. Indeed, while Web 2.0 helped people to easily produce data, it lead to various issues regarding how to protect and trust this data, especially when it comes to personal data. On the one hand, we are wondering how to protect our private information online, above all when this information is re-used at our disadvantage. On the other hand, information should not only be protected when being published by its owners, but tools should also help users to assess trustworthiness of third-party information online. According to our recent research works, both from a theoretical and practical point of view, we think that Semantic Web technologies can provide at least partial solutions to enable a 'trust and privacy layer' on top of the Social Web. Hence, this position paper will present our work on the topic, that is in our opinion, also particularly relevant to the mobile Web community, according to the advances of ubiquitous Social Networking with, e.g., microblogging from mobile devices.

[BDH+09] John Breslin, Stefan Decker, Manfred Hauswirth, Gearoid Hynes, Danh Le Phuoc, Alexandre Passant, Axel Polleres, Cornelius Rabsch, and Vinny Reynolds. Integrating social networks and sensor networks. In W3C Workshop on the Future of Social Networking, Barcelona, Spain, January 2009. [ .html ]
Sensors have begun to infiltrate people's everyday lives. They can provide information about a car's condition, can enable smart buildings, and are being used in various mobile applications, to name a few. Generally, sensors provide information about various aspects of the real world. Online social networks, another emerging trend over the past six or seven years, can provide insights into the communication links and patterns between people. They have enabled novel developments in communications as well as transforming the Web from a technical infrastructure to a social platform, very much along the lines of the original Web as proposed by Tim Berners-Lee, which is now often referred to as the Social Web. In this position paper, we highlight some of the interesting research areas where sensors and social networks can fruitfully interface, from sensors providing contextual information in context-aware and personalized social applications, to using social networks as “storage infrastructures” for sensor information.

[PKL+09] Axel Polleres, Thomas Krennwallner, Nuno Lopes, Jacek Kopecký, and Stefan Decker. XSPARQL Language Specification, January 2009. W3C member submission. [ http ]
XSPARQL is a query language combining XQuery and SPARQL for transformations between RDF and XML. XSPARQL subsumes XQuery and most of SPARQL (excluding ASK and DESCRIBE). This document defines the XSPARQL language.

[KLP09] Thomas Krennwallner, Nuno Lopes, and Axel Polleres. XSPARQL: Semantics, January 2009. W3C member submission. [ http ]
XSPARQL is a query language combining XQuery and SPARQL for transformations between RDF and XML. This document defines the semantics of XSPARQL.

[LKP+09] Nuno Lopes, Thomas Krennwallner, Axel Polleres, Waseem Akhtar, and Stéphane Corlosquet. XSPARQL: Implementation and Test-cases, January 2009. W3C member submission. [ http ]
XSPARQL is a query language combining XQuery and SPARQL for transformations between RDF and XML. This document provides a description of a prototype implementation of the language based on off-the-shelf XQuery and SPARQL engines. Along with a high-level description of the prototype the document presents a set of test queries and their expected output which are to be understood as illustrative help for possible other implementers.

[PKC+09] Alexandre Passant, Jacek Kopecký, Stéphane Corlosquet, Diego Berrueta, Davide Palmisano, and Axel Polleres. XSPARQL: Use cases, January 2009. W3C member submission. [ http ]
XSPARQL is a query language combining XQuery and SPARQL for transformations between RDF and XML. This document contains an overview of XSPARQL use cases within various scenarios.

[HHP09] Aidan Hogan, Andreas Harth, and Axel Polleres. Scalable authoritative owl reasoning for the web. International Journal on Semantic Web and Information Systems (IJSWIS), 5(2):49-90, 2009. [ .pdf ]
In this paper we discuss the challenges of performing reasoning on large scale RDF datasets from the Web. Using ter-Horst's pD* fragment of OWL as a base, we compose a rule-based framework for application to web data: we argue our decisions using observations of undesirable examples taken directly from the Web. We further temper our OWL fragment through consideration of “authoritative sources” which counter-acts an observed behaviour which we term “ontology hijacking”: new ontologies published on the Web re-defining the semantics of existing entities resident in other ontologies. We then present our system for performing rule-based forward-chaining reasoning which we call SAOR: Scalable Authoritative OWL Reasoner. Based upon observed characteristics of web data and reasoning in general, we design our system to scale: our system is based upon a separation of terminological data from assertional data and comprises of a lightweight in-memory index, on-disk sorts and file-scans. We evaluate our methods on a dataset in the order of a hundred million statements collected from real-world Web sources and present scale-up experiments on a dataset in the order of a billion statements collected from the Web.

[PM09] Axel Polleres and Malgorzata Mochol. Expertise bewerben und finden im Social Semantic Web. In Andreas Blumauer and Tassilo Pellegrini, editors, Social Semantic Web, pages 175-206. Springer, 2009. in German. [ .pdf ]
Im vorliegenden Beitrag diskutieren wir Rahmenbedingungen zur Kombination, Wiederverwendung und Erweiterung bestehender RDF Vokabulare im Social Semantic Web. Hierbei konzentrieren wir uns auf das Anwendungsszenario des Auffindens und Bewerbens von Experten im Web oder Intranet. Wir präsentieren, wie RDF Vokabulare mit zunehmendem Verbreitungsgrad im Semantic Web einerseits und de facto Standardformate, die von täglich verwendeten Applikationen benutzt werden, andererseits (z.B. vCard, iCal oder Dublin Core) kombiniert werden können, um konkrete Awendungsfälle der Expertensuche und zum Management von Expertise zu lösen. Unser Fokus liegt darauf aufzuzeigen, dass für praktische Anwendungsszenarien nicht notwendigerweise neue Ontologien entwickelt werden müssen, sondern der Schlüssel vielmehr in der Integration von bestehenden, weit verbreiteten, und sich ergänzenden Formaten zu einem kohärenten Netzwerk von Ontologien liegt. Dieser Ansatz garantiert sowohl direkte Anwendbarkeit als auch niedrige Einstiegsbarrieren für Semantic Web Technologien, sowie einfache Integrierbarkeit in bestehende Applikationen. Die im Web verfügbaren und verwendeten RDF Formate decken zwar einen großen Bereich der Aspekte zur Beschreibung von Personen und Expertisen ab, zeigen aber auch signifikante Überlappungen. Bisher gibt es wenig systematische Ansätze, um diese Vokabulare zu verbinden, sei es in Form von allgemeingültigen Praktiken, die definieren, wann welches Format zu benutzen ist, oder in Form von Regeln, die Überlappungen zwischen einzelnen Formaten formalisieren. Der vorliegende Artikel analysiert, wie bestehende Formate zur Beschreibung von Personen, Organisationen und deren Expertise kombiniert und wo nötig erweitert werden können. Darüber hinaus diskutieren wir Regelsprachen zur Beschreibung von Formatüberlappungen, sowie deren praktische Verwendbarkeit zur Erstellung eines Ontologie-Netzwerks zur Beschreibung von Experten.


2008


[dBHP+08] Jos de Bruijn, Stijn Heymans, David Pearce, Axel Polleres, and Edna Ruckhaus, editors. Proceedings of the 3rd International Workshop on Applications of Logic Programming to the (Semantic) Web and Web Services (ALPSWS2008), volume 434 of CEUR Workshop Proceedings, Udine, Italy, December 2008. CEUR-WS.org. [ http ]
Workshop Proceedings. This workshop was co-located with ICLP 2008.

[KLOP08] Philipp Kärger, Nuno Lopes, Daniel Olmedilla, and Axel Polleres. Towards logic programs with ordered and unordered disjunction. In Workshop on Answer Set Programming and Other Computing Paradigms (ASPOCP 2008), December 2008. [ .pdf ]
Logic Programming paradigms that allow for expressing preferences have drawn a lot of research interest over the last few years. Among them, the principle of ordered disjunction was developed to express totally ordered preferences for the alternatives in rule heads. In this paper we introduce an extension of this approach called Disjunctive Logic Programs with Ordered Disjunction (DLPOD) that combines ordered disjunction with common disjunction in rule heads. By this extension, we enhance the preference notions expressible with totally ordered disjunctions to partially ordered preferences. Furthermore, we show that computing optimal stable models for DLPODs still stays in Σ2p for head-cycle free programs and establish Σ3p upper bounds for the general case.

[HHP08a] Aidan Hogan, Andreas Harth, and Axel Polleres. SAOR: Authoritative Reasoning for the Web. In John Domingue and Chutiporn Anutariya, editors, Proceedings of the 3rd Asian Semantic Web Conference (ASWC 2008), volume 5367 of Lecture Notes in Computer Science (LNCS), pages 76-90, Bankok, Thailand, December 2008. [ .pdf ]
In this paper we discuss the challenges of performing reasoning on large scale RDF datasets from the Web. We discuss issues and practical solutions relating to reasoning over web data using a rule-based approach to forward-chaining; in particular, we identify the problem of ontology hijacking: new ontologies published on the Web re-defining the semantics of existing concepts resident in other ontologies. Our solution introduces consideration of authoritative sources. Our system is designed to scale, comprising file-scans and selected lightweight on-disk indices. We evaluate our methods on a dataset in the order of a hundred million statements collected from real-world Web sources.

[EPS08b] Jérôme Euzenat, Axel Polleres, and François Scharffe. SPARQL extensions for processing alignments. IEEE Intelligent Systems, 23(6):82-84, November 2008. Appeared as part of the article “Making Ontologies Talk: Knowledge Interoperability in the Semantic Web”, Monika Lanzenberger and Jennifer Sampson (eds.). [ http ]
We propose to extend the SPARQL query language to express mapping between ontologies. We use SPARQL queries as a mechanism for translating RDF data of one ontology to another. Such functionality lets users exploit instance data described in one ontology while they work with an application that's been designed for another. An example translation of FOAF (friend-of-a-friend) files into vCards shows how to use queries to extract data from the source ontology and generate new data for the target ontology.

[HHP08b] Aidan Hogan, Andreas Harth, and Axel Polleres. Scalable authoritative OWL reasoning on a billion triples. In ISWC2008 Semantic Web Challenge 2008 - Billion Triples Track, Karlsruhe, Germany, October 2008. [ .pdf ]
In this paper we present a scalable algorithm for performing a subset of OWL reasoning over web data using a rule-based approach to forward-chaining; in particular, we identify the problem of ontology hijacking: new ontologies published on the Web re-defining the semantics of existing concepts resident in other ontologies. Our solution introduces consideration of authoritative sources. We present the results of applying our methods on a re-crawl of the billion triple challenge dataset.

[MZN+08] Malgorzata Mochol, Anna V. Zhdanova, Lyndon Nixon, John Breslin, and Axel Polleres, editors. Proceedings of the 3rd Expert Finder Workshop on Personal Identification and Collaborations: Knowledge Mediation and Extraction (PICKME 2008), volume 403 of CEUR Workshop Proceedings, Karlsruhe, Germany, October 2008. CEUR-WS.org. [ http ]
Workshop Proceedings. This workshop was co-located with ISWC 2008. The Semantic Web, Social Networks and other emerging technology streams promise to enable finding experts more efficiently on a Web scale across boundaries. To leverage synergies among these streams, the ExpertFinder Initiative started in 2006 with the aim of devising vocabularies, rule extensions (for e.g. FOAF and SIOC) and best practices to annotate and extract expertise-relevant information from personal and organizational web pages, blogs, wikis, conferences, publication indexes, etc. Following two previous workshops - EFW and FEWS - PICKME2008 solocited new research contributions from the Semantic Web community towards the tasks of formally representing and reusing knowledge of skills and collaborations on the Web and consequently finding people according to their expertise.

[DPTD08] Renaud Delbru, Axel Polleres, Giovanni Tummarello, and Stefan Decker. Context dependent reasoning for semantic documents in sindice. In Proceedings of the 4th International Workshop on Scalable Semantic Web Knowledge Base Systems (SSWS 2008), Karlsruhe, Germany, October 2008. [ .pdf ]
The Sindice Semantic Web index provides search capabilities over today more than 30 million documents. A scalable reasoning mechanism for real-world web data is important in order to increase the precision and recall of the Sindice index by inferring useful information (e.g. RDF Schema features, equality, property characteristic such as inverse functional properties or annotation properties from OWL). In this paper, we introduce our notion of context dependent reasoning for RDF documents published on the Web according to the linked data principle. We then illustrate an efficient methodology to perform context dependent RDFS and partial OWL inference based on a persistent TBox composed of a network of web ontologies. Finally we report preliminary evaluation results of our implementation underlying the Sindice web data index.

[FHL+08] Alberto Fernandez, Conor Hayes, Nikos Loutas, Vassilios Peristeras, Axel Polleres, and Konstantinos Tarabanis. Closing the Service Discovery Gap by Collaborative Tagging and Clustering Techniques. In Proceedings of 2nd Internatioal Workshop on Service Matchmaking and Resource Retrieval in the Semantic Web (SMR2 2008), Karlsruhe, Germany, October 2008. [ .pdf ]
Whereas the number of services that are provided online is growing rapidly, current service discovery approaches seem to have problems fulfilling their objectives. These existing approaches are hampered by the complexity of underlying semantic service models and by the fact that they try to impose a technical vocabulary to users. This leads to what we call the service discovery gap. In this paper we envision an approach that allows users first to query or browse services using free text tags, thus providing an interface in terms of the users' vocabulary instead of the service's vocabulary. Unlike simple keyword search, we envision tag clouds associated with services themselves as semantic descriptions carrying collaborative knowledge about the service that can be clustered hierarchically, forming lightweight “ontologies”. Besides tag-based discovery only describing the service on a global view, we envision refined tags and refined search/discovery in terms of the concepts that are common to all current semantic service description models, i.e. input, output, and operation. We argue that Service matching can be achieved, by applying tag-cloud-based service similarity on the one hand and by clustering services using case based indexing and retrieval techniques on the other hand.

[BBM+08] Cristina Baroglio, Piero A. Bonatti, Jan Maluszynski, Massimo Marchiori, Axel Polleres, and Sebastian Schaffert, editors. Reasoning Web 2008, volume 5224 of Lecture Notes in Computer Science (LNCS). Springer, San Servolo Island, Venice, Italy, September 2008. [ http ]
The Reasoning Web summer school series is a well-established event, attracting experts from academy and industry as well as PhD students interested in foundational and applicative aspects of the Semantic Web. This volume contains the lecture notes of the fourth edition, that took place in Venice, Italy, in September 2008. This year, the school has been focussed on some important application domains where semantic web techniques proved to be particularly effective or promising in tackling application needs.

[KPP08] Matthias Klusch, Michal Pechoucek, and Axel Polleres, editors. Cooperative Information Agents XII, volume 5180 of Lecture Notes in Computer Science (LNCS), Prague, Czech Republic, September 2008. Springer. [ http ]
The objective of the international workshop series on cooperative information agents (CIA), since its establishment in 1997, is to provide a distinguished, interdisciplinary forum for researchers, programmers, and managers to get informed about, present, and discuss latest high quality results in research and development of agent-based intelligent and cooperative information systems, and applications for the Internet, Web and Semantic Web. Each event of the series offers regular and invited talks of excellence that are given by renown experts in the field, a selected set of system demonstrations, and honors innovative research and development of information agents by means of a best paper award, and respectively, a system innovation award. The proceedings of the series are regularly published as volumes of the Lecture Notes in Artificial Intelligence (LNAI) series of the Springer Verlag. In keeping with its tradition, this year's workshop featured a sequence of regular and invited talks of excellence given by leading researchers covering a broad area of topics of interest. In particular, CIA 2008 featured five invited and nineteen regular papers selected from thirty-eight submissions. The result of the peer-review of all contributions is included in this volume that is, as we think, again rich of interesting, inspiring, and advanced work on research and development of intelligent information agents worldwide.

[EIKP08] Thomas Eiter, Giovambattista Ianni, Thomas Krennwallner, and Axel Polleres. Rules and ontologies for the semantic web. In Cristina Baroglio, Piero A. Bonatti, Jan Maluszynski, Massimo Marchiori, Axel Polleres, and Sebastian Schaffert, editors, Reasoning Web 2008, volume 5224 of Lecture Notes in Computer Science (LNCS), pages 1-53. Springer, San Servolo Island, Venice, Italy, September 2008. [ .pdf ]
Rules and ontologies play a key role in the layered architecture of the Semantic Web, as they are used to ascribe meaning to, and to reason about, data on the Web. While the Ontology Layer of the Semantic Web is quite developed, and the Web Ontology Language (OWL) is a W3C recommendation since a couple of years already, the rules layer is far less developed and an active area of research; a number of initiatives and proposals have been made so far, but no standard as been released yet. Many implementations of rule engines are around which deal with Semantic Web data in one or another way. This article gives a comprehensive, although not exhaustive, overview of such systems, describes their supported languages, and sets them in relation with theoretical approaches for combining rules and ontologies as foreseen in the Semantic Web architecture. In the course of this, we identify desired properties and common features of rule languages and evaluate existing systems against their support. Furthermore, we review technical problems underlying the integration of rules and ontologies, and classify representative proposals for theoretical integration approaches into different categories.

[TDB+08] Hong-Linh Truong, Schahram Dustdar, Dino Baggio, Stéphane Corlosquet, Christoph Dorn, Giovanni Giuliani, Robert Gombotz, Yi Hong, Pete Kendal, Christian Melchiorre, Sarit Moretzky, Sébastien Peray, Axel Polleres, Stephan Reiff-Marganiec, Daniel Schall, Simona Stringa, Marcel Tilly, and Hong Qing Yu. incontext: a pervasive and collaborative working environment for emerging team forms. In International Symposium on Applications and the Internet (SAINT 2008), pages 118-125, Turku, Finland, July 2008. IEEE Computer Society. [ .pdf ]
Participants in current team collaborations belong to different organizations, work on multiple objectives at the same time, and frequently change locations. They use different devices and infrastructures in collaboration processes that can last from a few hours to several years. All these factors pose new challenges to the development of collaborative working environments (CWEs). Existing CWEs are unable to support emerging teams because diverse collaboration services are not well integrated or adapting to the team context. We present the inContext approach to providing a novel pervasive CWE infrastructure for emerging team forms. inContext aggregates disparate collaboration services using Web services and Semantic Web technologies and provides a platform that captures diverse dynamic aspects of team collaborations. By utilizing runtime and historical context and interaction information, adaptation techniques can be deployed to cope with the changes of emerging teams.

[AKKP08] Waseem Akhtar, Jacek Kopecky, Thomas Krennwallner, and Axel Polleres. XSPARQL: Traveling between the XML and RDF worlds - and avoiding the XSLT pilgrimage. In Proceedings of the 5th European Semantic Web Conference (ESWC2008), volume 5021 of Lecture Notes in Computer Science (LNCS), pages 432-447, Tenerife, Spain, June 2008. Springer. Nominated for best paper award. [ .pdf ]
With currently available tools and languages, translating between an existing XML format and RDF is a tedious and error-prone task. The importance of this problem is acknowledged by the W3C GRDDL working group who faces the issue of extracting RDF data out of existing HTML or XML files, as well as by the Web service community around SAWSDL, who need to perform lowering and lifting between RDF data from a semantic client and XML messages for a Web service. However, at the moment, both these groups rely solely on XSLT transformations between RDF/XML and the respective other XML format at hand. In this paper, we propose a more natural approach for such transformations based on merging XQuery and SPARQL into the novel language XSPARQL. We demonstrate that XSPARQL provides concise and intuitive solutions for mapping between XML and RDF in either direction, addressing both the use cases of GRDDL and SAWSDL. We also provide and describe an initial implementation of an XSPARQL engine, available for user evaluation.

[PPWW08] Reinhard Pichler, Axel Polleres, Fang Wei, and Stefan Woltran. Entailment for domain-restricted RDF. In Proceedings of the 5th European Semantic Web Conference (ESWC2008), volume 5021 of Lecture Notes in Computer Science (LNCS), pages 200-214, Tenerife, Spain, June 2008. Springer. [ .pdf ]
We introduce domain-restricted RDF (dRDF) which allows to associate an RDF graph with a fixed, finite domain that interpretations for it may range over. We show that dRDF is a real extension of RDF and discuss impacts on the complexity of entailment in dRDF. The entailment problem represents the key reasoning task for RDF and is well known to be NP-complete. Remarkably, we show that the restriction of domains in dRDF raises the complexity of entailment from NP- to ΠP2-completeness. In order to lower complexity of entailment for both domain-restricted and unrestricted graphs, we take a closer look at the graph structure. For cases where the structure of RDF graphs is restricted via the concept of bounded treewidth, we prove that the entailment is tractable for unrestricted graphs and coNP-complete for domain-restricted graphs.

[MPP+08] Christian Morbidoni, Danh Le Phuoc, Axel Polleres, Matthias Samwald, and Giovanni Tummarello. Previewing semantic web pipes. In Proceedings of the 5th European Semantic Web Conference (ESWC2008), pages 843-848, Tenerife, Spain, June 2008. Springer. Demo Paper. [ .pdf ]
In this demo we present a first implementation of Semantic Web Pipes, a powerful tool to build RDF-based mashups. Semantic Web pipes are defined in XML and when executed they fetch RDF graphs on the Web, operate on them, and produce an RDF output which is itself accessible via a stable URL. Humans can also use pipes directly thanks to HTML wrapping of the pipe parameters and outputs. The implementation we will demo includes an online AJAX pipe editor and execution engine. Pipes can be published and combined thus fostering collaborative editing and reuse of data mashups.

[TDC+08] Hong-Linh Truong, Christoph Dorn, Giovanni Casella, Axel Polleres, Stephan Reiff-Marganiec, and Schahram Dustdar. incontext: On coupling and sharing context for collaborative teams. In 14th International Conference of Concurrent Enterprising (ICE 2008), pages 225-232, Lisboa, Portugal, June 2008. [ .pdf ]
Present team members have difficulties in keeping the relations between their various, concurrent activities due to the lack of suitable tools supporting context coupling and sharing. Furthermore, collaboration services are hardly aware of related context of team members and their activities. Such awareness is required to adapt to the dynamics of collaborative teams. In this paper, we discuss the context coupling techniques provided by the inContext project. Utilizing the concept of activity-based context and Web services techniques, we can couple individual and team contexts at runtime, thus improving the context-awareness and adaptation of collaboration services such as email, shared calendars, instant messaging and document management.

[EPS08a] Jérôme Euzenat, Axel Polleres, and François Scharffe. Processing ontology alignments with SPARQL. In International Workshop on Ontology Alignment and Visualization - OnAV'08, Proceedings of the Second International Conference on Complex, Intelligent and Software Intensive Systems, pages 913-917, Barcelona, Spain, March 2008. IEEE Computer Society. [ .pdf ]
Solving problems raised by heterogeneous ontologies can be achieved by matching the ontologies and processing the resulting alignments. This is typical of data mediation in which the data must be translated from one knowledge source to another. In this position paper we propose to solve the data translation problem, i.e. the processing part, using the SPARQL query language. Indeed, such a language is particularly adequate for extracting data from one ontology and, through its CONSTRUCT statement, for generating new data. We present examples of such transformations, but we also present a set of example correspondences illustrating the needs for particular representation constructs, such as aggregates, value-generating built-in functions and paths, which are missing from SPARQL. Hence, we advocate the use of two SPARQL extensions providing these missing features.


2007


[MPT07b] Christian Morbidoni, Axel Polleres, and Giovanni Tummarello. Who the FOAF knows Alice? RDF Revocation in DBin 2.0. In 4th Italian Semantic Web Workshop SEMANTIC WEB APPLICATIONS AND PERSPECTIVES (SWAP), Bari, Italy, December 2007. [ .pdf ]
In this paper we take a view from the bottom to RDF(S) reasoning. We discuss some issues and requirements on reasoning towards effectively building Semantic Web Pipes, aggregating and patching RDF data from various distributed sources. Even if we leave out complex description logics reasoning and restrict ourselves to the RDF world, it turns out that some problems, in particular how to deal with contradicting RDF statements and patching RDF graphs, do not yet find their proper solutions within the current Semantic Web Stack. Besides theoretical solutions which involve full DL reasoning, we believe that more practical and probably more scalable solutions are conceivable one of which we discuss in this paper. Namely, we provide means to express revocations in RDF and resolve such revocations by means of a specialized RDF merge procedure. We have implemented this conflict-resolving merge procedure in the DBin 2.0 system.

[HPD07] Andreas Harth, Axel Polleres, and Stefan Decker. Towards a social provenance model for the web. In Workshop on Principles of Provenance (PrOPr), Edinburgh, Scotland, November 2007. [ .pdf ]
In this position paper we firstly present the established notion of provenance on the Semantic Web (also referred to as named graphs or contexts), and secondly argue for the benefit of adding to the pure technical notion of provenance a social dimension to associate provenance with the originator (typically a person) of a given piece of information.

[PSS07] Axel Polleres, François Scharffe, and Roman Schindlauer. SPARQL++ for mapping between RDF vocabularies. In OTM 2007, Part I : Proceedings of the 6th International Conference on Ontologies, DataBases, and Applications of Semantics (ODBASE 2007), volume 4803 of Lecture Notes in Computer Science (LNCS), pages 878-896, Vilamoura, Algarve, Portugal, November 2007. Springer. [ .pdf ]
Lightweight ontologies in the form of RDF vocabularies such as SIOC, FOAF, vCard, etc. are increasingly being used and exported by “serious” applications recently. Such vocabularies, together with query languages like SPARQL also allow to syndicate resulting RDF data from arbitrary Web sources and open the path to finally bringing the Semantic Web to operation mode. Considering, however, that many of the promoted lightweight ontologies overlap, the lack of suitable standards to describe these overlaps in a declarative fashion becomes evident. In this paper we argue that one does not necessarily need to delve into the huge body of research on ontology mapping for a solution, but itself might - with extensions such as external functions and aggregates - serve as a basis for declaratively describing ontology mappings. We provide the semantic foundations and a path towards implementation for such a mapping language by means of a translation to Datalog with external predicates.

[MPT07a] Christian Morbidoni, Axel Polleres, and Giovanni Tummarello. Who the FOAF knows Alice? A needed step towards Semantic Web Pipes. In ISWC 2007 Workshop on New forms of Reasoning for the Semantic Web: Scaleable, Tolerant and Dynamic, Busan, Korea, November 2007. [ .pdf ]
In this paper we take a view from the bottom to RDF(S) reasoning. We discuss some issues and requirements on reasoning towards effectively building Semantic Web Pipes, aggregating RDF data from various distributed sources. If we leave out complex description logics reasoning and restrict ourselves to the RDF world, it turns out that some problems, in particular how to deal with contradicting RDF statements, do not yet find their proper solutions within the current Semantic Web Stack. Besides theoretical solutions which involve full DL reasoning, we believe that more practical and probably more scalable solutions are conceivable one of which we discuss in this paper, namely, expressing and resolving conflicting RDF statements by means of a specialized RDF merge procedure. We implemented this conflict-resolving merge procedure in the DBin system.

[dNLP+07] Tommaso di Noia, Rubén Lara, Axel Polleres, Ioan Toma, Takahiro Kawamura, Matthias Klusch, Abraham Bernstein, Massimo Paolucci, Alain Leger, and David Martin, editors. Proceedings of the SMR2 2007 Workshop on Service Matchmaking and Resource Retrieval in the Semantic Web (SMR2 2007), volume 243 of CEUR Workshop Proceedings, Busan, Korea, November 2007. CEUR-WS.org. [ http ]
Workshop Proceedings. This workshop was co-located with ISWC 2007 + ASWC 2007.

[FPO07] Alberto Fernandez, Axel Polleres, and Sascha Ossowski. Towards Fine-grained Service Matchmaking by Using Concept Similarity. In Proceedings of the SMR2 2007 Workshop on Service Matchmaking and Resource Retrieval in the Semantic Web (SMR2 2007), volume 243 of CEUR Workshop Proceedings, pages 31-45, Busan, Korea, November 2007. CEUR-WS.org. [ .pdf ]
Several description frameworks to semantically describe and match services on the one hand and service requests on the other have been presented in the literature. Many of the current proposals for defining notions of match between service advertisements and requests are based on subsumption checking in more or less expressive Description Logics, thus providing boolean match functions, rather than a fine-grained, numerical degree of match. By contrast, concept similarity measures investigated in the DL literature explicitely include such a quantitative notion. In this paper we try to take a step forward in this area by means of an analysis of existing approaches from both semantic web service matching and concept similarity, and provide preliminary ideas on how to combine these two building blocks in a unified service selection framework.

[HPP+07] Stijn Heymans, David Pearce, Axel Polleres, Edna Ruckhaus, and Gopal Gupta, editors. ALPSWS2007: 2nd International Workshop on Applications of Logic Programming in the Semantic Web and Semantic Web Services. Proceedings, volume 287 of CEUR Workshop Proceedings, Porto, Portugal, September 2007. CEUR-WS.org. [ http ]
Workshop Proceedings. This workshop was co-located with ICLP 2007.

[PS07] Axel Polleres and Roman Schindlauer. dlvhex-sparql: A SPARQL-compliant query engine based on dlvhex. In 2nd International Workshop on Applications of Logic Programming to the Web, Semantic Web and Semantic Web Services (ALPSWS2007), volume 287 of CEUR Workshop Proceedings, pages 3-12, Porto, Portugal, September 2007. CEUR-WS.org. [ .pdf ]
This paper describes the dlvhex SPARQL plugin, a query processor for the upcoming Semantic Web query language standard by W3C. We report on the implementation of this languages using dlvhex, a flexible plugin system on top of the DLV solver. This work advances our earlier translation based on the semantics by Perez et al. towards an engine which is fully compliant to the official SPARQL specification. As it turns out, the differences between these two definitions of SPARQL, which might seem moderate at first glance, need some extra machinery. We also briefly report the status of implementation, and extensions currently being implemented, such as handling of aggregates, nested CONSTRUCT queries in the spirit of networked RDF graphs, or partially support of RDFS entailment. For such extensions a tight integration of SPARQL query processing and Answer-Set Programming, the underlying logic programming formalism of our engine, turns out to be particularly useful, as the resulting programs can actually involve unstratified negation.

[BKPP07] Harold Boley, Michael Kifer, Paula-Lavinia Pātrânjan, and Axel Polleres. Rule interchange on the web. In Reasoning Web 2007, volume 4636 of Lecture Notes in Computer Science (LNCS), pages 269-309. Springer, September 2007. [ .pdf ]
Rules play an increasingly important role in a variety of Semantic Web applications as well as in traditional IT systems. As a universal medium for publishing information, the Web is envisioned to become the place for publishing, distributing, and exchanging rule-based knowledge. Realizing the importance and the promise of this vision, the W3C has created the Rule Interchange Format Working Group (RIF WG) and chartered it to develop an interchange format for rules in alignment with the existing standards in the Semantic Web architecture stack. However, creating a generally accepted interchange format is by no means a trivial task. First, there are different understandings of what a “rule” is. Researchers and practitioners distinguish between deduction rules, normative rules, production rules, reactive rules, etc. Second, even within the same category of rules, systems use different (often incompatible) semantics and syntaxes. Third, existing Semantic Web standards, such as RDF and OWL, show incompatibilities with many kinds of rule languages at a conceptual level. This article discusses the role that different kinds of rule languages and systems play on the Web, illustrates the problems and opportunities in exchanging rules through a standardized format, and provides a snapshot of the current work of the W3C RIF WG.

[BBB+07] Uldis Bojars, John G. Breslin, Diego Berrueta, Dan Brickley, Stefan Decker, Sergio Fernández, Christoph Görn, Andreas Harth, Tom Heath, Kingsley Idehen, Kjetil Kjernsmo, Alistair Miles, Alexandre Passant, Axel Polleres, Luis Polo, and Michael Sintek. SIOC Core Ontology Specification, June 2007. W3C member submission. [ http ]
The SIOC (Semantically-Interlinked Online Communities) Core Ontology provides the main concepts and properties required to describe information from online communities (e.g., message boards, wikis, weblogs, etc.) on the Semantic Web. This document contains a detailed description of the SIOC Core Ontology.

[dBPPV07] Jos de Bruijn, David Pearce, Axel Polleres, and Agustín Valverde. Quantified equilibrium logic and hybrid rules. In Massimo Marchiori, Jeff Z. Pan, and Christian de Sainte Marie, editors, First International Conference on Web Reasoning and Rule Systems (RR2007), volume 4524 of Lecture Notes in Computer Science (LNCS), pages 58-72, Innsbruck, Austria, June 2007. Springer. [ .pdf ]
In the ongoing discussion about combining rules and Ontologies on the Semantic Web a recurring issue is how to combine first-order classical logic with nonmonotonic rule languages. Whereas several modular approaches to define a combined semantics for such hybrid knowledge bases focus mainly on decidability issues, we tackle the matter from a more general point of view. In this paper we show how Quantified Equilibrium Logic (QEL) can function as a unified framework which embraces classical logic as well as disjunctive logic programs under the (open) answer set semantics. In the proposed variant of QEL we relax the unique names assumption, which was present in earlier versions of QEL. Moreover, we show that this framework elegantly captures the existing modular approaches for hybrid knowledge bases in a unified way.

[AMBB+07] Boanerges Aleman-Meza, Uldis Bojars, Harold Boley, John G. Breslin, Malgorzata Mochol, Lyndon J.B. Nixon, Axel Polleres, and Anna V. Zhdanova. Combining RDF vocabularies for expert finding. In Enrico Franconi, Michael Kifer, and Wolfgang May, editors, Proceedings of the 4th European Semantic Web Conference (ESWC2007), volume 4519 of Lecture Notes in Computer Science (LNCS), pages 235-250, Innsbruck, Austria, June 2007. Springer. Slides available at http://www.polleres.net/publications/alem-etal-2007eswc-slides.pdf. [ .pdf ]
This paper presents a framework for the reuse and extension of existing, established vocabularies in the Semantic Web. Driven by the primary application of expert finding, we will explore the reuse of vocabularies that have attracted a considerable user community already (FOAF, SIOC, etc.) or are derived from de facto standards used in tools or industrial practice (such as vCard, iCal and Dublin Core). This focus guarantees direct applicability and low entry barriers, unlike when devising a new ontology from scratch. The Web is already populated with several vocabularies which complement each other (but also have considerable overlap) in that they cover a wide range of necessary features to adequately describe the expert finding domain. Little effort has been made so far to identify and compare existing approaches, and to devise best practices on how to use and extend various vocabularies conjointly. It is the goal of the recently started ExpertFinder initiative to fill this gap. In this paper we present the ExpertFinder framework for reuse and extension of existing vocabularies in the Semantic Web. We provide a practical analysis of overlaps and options for combined use and extensions of several existing vocabularies, as well as a proposal for applying rules and other enabling technologies to the expert finding task.

[AGP+07] Marcelo Arenas, Claudio Gutierrez, Bijan Parsia, Jorge Pérez, Axel Polleres, and Andy Seaborne. SPARQL - where are we? current state, theory and practice, June 2007. Slides available at http://www.polleres.net/sparqltutorial/. [ http ]
Tutorial at the 4th European Semantic Web Conference (ESWC2007)

[BFM+07] Martin Brain, Wolfgang Faber, Marco Maratea, Axel Polleres, Torsten Schaub, and Roman Schindlauer. What should an ASP solver output? a multiple position paper. In Marina De Vos and Torsten Schaub, editors, First International Workshop on Software Engineering for Answer Set Programming 2007 (SEA'07), pages 26-37, Tempe, AZ, May 2007. [ .pdf ]
This position paper raises some issues regarding the output of solvers for Answer Set Programming and discusses experiences made in several different settings. The first set of issues was raised in the context of the first ASP system competition, which led to a first suggestion for a standardised yet miniature output format. We then turn to experiences made in related fields, like Satisfiability Checking, and finally adopt an application point of view by investigating interface issues both with simple tools and in the context of the Semantic Web and query answering.

[PPVW07] David Pearce, Axel Polleres, Agustín Valverde, and Stefan Woltran, editors. Workshop on Correspondence and Equivalence for Nonmonotonic Theories (CENT 2007) Working Notes, volume 265 of CEUR Workshop Proceedings, Tempe, AZ, May 2007. CEUR-WS.org. [ http ]
Workshop Proceedings. This workshop was co-located with LPNMR 2007.

[Pol07] Axel Polleres. From SPARQL to rules (and back). In Proceedings of the 16th World Wide Web Conference (WWW2007), pages 787-796, Banff, Canada, May 2007. ACM Press. Extended technical report version available at http://www.polleres.net/TRs/GIA-TR-2006-11-28.pdf, slides available at http://www.polleres.net/publications/poll-2007www-slides.pdf. [ http ]
As the data and ontology layers of the Semantic Web stack have achieved a certain level of maturity in standard recommendations such as RDF and OWL, the current focus lies on two related aspects. On the one hand, the definition of a suitable query language for RDF, SPARQL, is close to recommendation status within the W3C. The establishment of the rules layer on top of the existing stack on the other hand marks the next step to be taken, where languages with their roots in Logic Programming and Deductive Databases are receiving considerable attention. The purpose of this paper is threefold. First, we discuss the formal semantics of SPARQL extending recent results in several ways. Second, we provide translations from SPARQL to Datalog with negation as failure. Third, we propose some useful and easy to implement extensions of SPARQL, based on this translation. As it turns out, the combination serves for direct implementations of SPARQL on top of existing rules engines as well as a basis for more general rules and query languages on top of RDF.

[LLP+07] Holger Lausen, Rubén Lara, Axel Polleres, Jos de Bruijn, and Dumitru Roman. Chapter 7: Description - semantic annotation for web services. In Rudi Studer, Stephan Grimm, and Andreas Abecker, editors, Semantic Web Services, pages 179-209. Springer, 2007. [ http ]
Web Services have added a new level of functionality to the current Web, making the first step to achieve seamless integration of distributed components. Nevertheless, current Web Service technologies only address the syntactical aspects of a Web Service and, therefore, only provide a set of rigid services that cannot adapt to a changing environment without human intervention. The human programmer has to be kept in the loop and scalability as well as economy of Web Services are limited. The description of Web Services in a machine-understandable fashion is expected to have a great impact in areas of e-Commerce and Enterprise Application Integration, as it can enable dynamic and scalable cooperation between different systems and organisations. These great potential benefits have led to the establishment of an important research activity, both in industry and in academia, which aims at realising Semantic Web Services. This chapter outlines aspects of the description of semantic Web Services.

[BBAM+07] John G. Breslin, Uldis Bojars, Boanerges Aleman-Meza, Harold Boley, Malgorzata Mochol, Lyndon J.B. Nixon, Axel Polleres, and Anna V. Zhdanova. Finding experts using internet-based discussions in online communities and associated social networks. In 1st International ExpertFinder Workshop, January 2007. [ .pdf ]
This position paper on expert finding presents a conceptual framework for the reuse and interlinking of existing, well-established vocabularies in the Semantic Web. Such a framework can be used to connect people with people, based on joint or complementing interests (e.g. the need to develop specific new or existing skills for upcoming projects). Driven by a requirement to find experts using the profiles of people in social networks and using the content they create in online communities, we are exploring the usage of vocabularies in these domains that have already gained considerable momentum and that have suitable concepts for this application area. We will present the relevant properties of the FOAF ontology for matching people and their skills in social networks, then detail the SIOC project and methods for identifying relevant discussion topics/individuals, and finally we will outline a combinatory scenario that will allow people to find individuals with the desired expertise in a particular domain of interest.

[dBEPT07] Jos de Bruijn, Thomas Eiter, Axel Polleres, and Hans Tompits. Embedding non-ground logic programs into autoepistemic logic for knowledge-base combination. In Twentieth International Joint Conference on Artificial Intelligence (IJCAI'07), pages 304-309, Hyderabad, India, January 2007. AAAI. [ .pdf ]
In the context of the Semantic Web, several approaches to the combination of ontologies, given in terms of theories of classical first-order logic, and rule bases have been proposed. They either cast rules into classical logic or limit the interaction between rules and ontologies. Autoepistemic logic (AEL) is an attractive formalism which allows to overcome these limitations, by serving as a uniform host language to embed ontologies and nonmonotonic logic programs into it. For the latter, so far only the propositional setting has been considered. In this paper, we present several embeddings of normal and disjunctive non-ground logic programs under the stable-model semantics into first-order AEL, and compare them in combination with classical theories, with respect to stable expansions and autoepistemic consequences. Our results reveal differences and correspondences of the embeddings and provide a useful guidance in the choice of a particular embedding for knowledge combination.


2006


[dBPPV06] Jos de Bruijn, David Pearce, Axel Polleres, and Agustín Valverde. A logic for hybrid rules. In RuleML 2006 Workshop: Ontology and Rule Integration, November 2006. [ .pdf ]
In the ongoing discussion about rule extensions for Ontology languages on the Semantic Web a recurring issue is how to combine first-order classical logic with nonmonotonic rule languages. Whereas several modular approaches to define a combined semantics for such hybrid knowledge bases focus mainly on decidability issues, we tackle the matter from a more general point of view. In this paper we show how Quantified Equilibrium Logic (QEL) can function as a unified framework that embraces classical logic as well as disjunctive logic programs under the (open) answer set semantics. In the proposed variant of QEL we relax the unique names assumption from earlier versions. Moreover, we show that this framework elegantly captures several modular approaches to nonmonotonic semantics for hybrid knowledge bases.

[PS06] Axel Polleres and Roman Schindlauer. SPAR2QL: From SPARQL to rules. In International Semantic Web Conference (ISWC2006 - Posters Track), Athens, GA, USA, November 2006. Abstract, the full poster is available at http://www.polleres.net/publications/poll-schi-2006-poster.pdf. [ .pdf ]
As the data and ontology layers of the Semantic Web stack have achieved a certain level of maturity in standard recommendations such as RDF and OWL, the current focus lies on two related aspects. On the one hand, the definition of a suitable query language for RDF, SPARQL, has just reached candidate recommendation status within the W3C. The establishment of the rules layer on top of the existing stack on the other hand marks the next step to be tackled, where especially languages with their roots in Logic Programming and Deductive Databases are receiving considerable attention. In this work we try to bridge the gap between these two efforts by providing translations between SPARQL and Datalog extended with negation and external built-in predicates. It appears that such a combination serves both as an underpinning for a more general rules and query language on top of RDF and SPARQL as well as for direct implementations of SPARQL on top of existing rules engines. Our prototype implementation is based on the datalog engine DLV. As it turns out, features of the language of this system can be fruitfully combined with SPARQL.

[EIP+06] Thomas Eiter, Giovambattista Ianni, Axel Polleres, Roman Schindlauer, and Hans Tompits. Reasoning with rules and ontologies. In P. Barahona et al., editor, Reasoning Web 2006, volume 4126 of Lecture Notes in Computer Science (LNCS), pages 93-127. Springer, September 2006. [ .pdf ]
For realizing the Semantic Web vision, extensive work is underway for getting the layers of its conceived architecture ready. Given that the Ontology Layer has reached a certain level of maturity with W3C recommendations such as RDF and the OWL Web Ontology Language, current interest focuses on the Rules Layer and its integration with the Ontology Layer. Several proposals have been made for solving this problem, which does not have a straightforward solution due to various obstacles. One of them is the fact that evaluation principles like the closed-world assumption, which is common in rule languages, are usually not adopted in ontologies. Furthermore, naively adding rules to ontologies raises undecidability issues. In this paper, after giving a brief overview about the current state of the Semantic-Web stack and its components, we will discuss nonmonotonic logic programs under the answer-set semantics as a possible formalism of choice for realizing the Rules Layer. We will briefly discuss open issues in combining rules and ontologies, and survey some existing proposals to facilitate reasoning with rules and ontologies. We will then focus on description-logic programs (or dl-programs, for short), which realize a transparent integration of rules and ontologies supported by existing reasoning engines, based on the answer-set semantics. We will further discuss a generalization of dl-programs, viz. HEX-programs, which offer access to different ontologies as well as higher-order language constructs.

[PDGdB06] Axel Polleres, Stefan Decker, Gopal Gupta, and Jos de Bruijn, editors. ALPSWS2006: Applications of Logic Programming in the Semantic Web and Semantic Web Services. Proceedings, volume 196 of CEUR Workshop Proceedings, Seattle, WA, August 2006. CEUR-WS.org. [ http ]
Workshop Proceedings. This workshop was co-located with ICLP 2006.

[dBEPT06] Jos de Bruijn, Thomas Eiter, Axel Polleres, and Hans Tompits. On representational issues about combinations of classical theories with nonmonotonic rules. In Proceedings of the 1st International Conference on Knowledge Science, Engineering and Management (KSEM'06), volume 4092 of Lecture Notes in Computer Science (LNCS), pages 1-22, Gullin, China, August 2006. Springer. Invited paper. [ .pdf ]
In the context of current efforts around Semantic-Web languages, the combination of classical theories in classical first-order logic (and in particular of ontologies in various description logics) with rule languages rooted in logic programming is receiving considerable attention. Existing approaches such as SWRL, dl-programs, and DL+log, differ significantly in the way ontologies interact with (nonmonotonic) rules bases. In this paper, we identify fundamental representational issues which need to be addressed by such combinations and formulate a number of formal principles which help to characterize and classify existing and possible future approaches to the combination of rules and classical theories. We use the formal principles to explicate the underlying assumptions of current approaches. Finally, we propose a number of settings, based on our analysis of the representational issues and the fundamental principles underlying current approaches.

[dBLPF06] Jos de Bruijn, Holger Lausen, Axel Polleres, and Dieter Fensel. The web service modeling language: An overview. In Proceedings of the 3rd European Semantic Web Conference (ESWC2006), volume 4011 of Lecture Notes in Computer Science (LNCS), Budva, Montenegro, June 2006. Springer. Nominated for the 7 Years Most Influential ESWC Paper award at ESWC2013. [ .pdf ]
The Web Service Modeling Language (WSML) is a language for the specification of different aspects of Semantic Web Services. It provides a formal language for the Web Service Modeling Ontology WSMO which is based on well-known logical formalisms, specifying one coherent language framework for the description of Semantic Web Services, starting from the intersection of Datalog and the Description Logic SHIQ. This core language is extended in the directions of Description Logics and Logic Programming in a principled manner with strict layering. WSML distinguishes between conceptual and logical modeling in order to facilitate users who are not familiar with formal logic, while not restricting the expressive power of the language for the expert user. IRIs play a central role in WSML as identifiers. Furthermore, WSML defines XML and RDF serializations for inter-operation over the Semantic Web.

[PFH06] Axel Polleres, Cristina Feier, and Andreas Harth. Rules with contextually scoped negation. In Proceedings of the 3rd European Semantic Web Conference (ESWC2006), volume 4011 of Lecture Notes in Computer Science (LNCS), pages 332-347, Budva, Montenegro, June 2006. Springer. [ .pdf ]
Knowledge representation formalisms used on the Semantic Web adhere to a strict open world assumption. Therefore, nonmonotonic reasoning techniques are often viewed with scepticism. Especially negation as failure, which intuitively adopts a closed world view, is often claimed to be unsuitable for the Web where knowledge is notoriously incomplete. Nonetheless, it was suggested in the ongoing discussions around rules extensions for languages like RDF(S) or OWL to allow at least restricted forms of negation as failure, as long as negation has an explicitly defined, finite scope. Yet clear definitions of such “scoped negation” as well as formal semantics thereof are missing. We propose logic programs with contexts and scoped negation and discuss two possible semantics with desirable properties. We also argue that this class of logic programs can be viewed as a rule extension to a subset of RDF(S).

[EIPS06] Thomas Eiter, Giovambattista Ianni, Axel Polleres, and Roman Schindlauer. Answer set programming for the semantic web, June 2006. Slides available at http://asptut.gibbi.com/. [ http ]
Tutorial at the 3rd European Semantic Web Conference (ESWC2006)

[PLL06] Axel Polleres, Holger Lausen, and Rubén Lara. Semantische Beschreibung von Web Services. In Tassilo Pellegrini and Andreas Blumauer, editors, Semantic Web - Wege zur vernetzten Wissensgesellschaft. Springer, June 2006. (in German). [ .pdf ]
In diesem Kapitel werden Anwendungsgebiete und Ansätze für die semantische Beschreibung von Web Services behandelt. Bestehende Web Service Technologien leisten einen entscheidenden Beitrag zur Entwicklung verteilter Anwendungen dadurch, dass weithin akzeptierte Standards vorliegen, die die Kommunikation zwischen Anwendungen bestimmen und womit deren Kombination zu komplexeren Einheiten erm öglicht wird. Automatisierter Mechanismen zum Auffinden geeigneter Web Services und deren Komposition dagegen werden von bestehenden Technologien in vergleichsweise geringem Mas unterstützt. Ähnlich wie bei der Annotation statischer Daten im “Semantic Web” setzen Forschung und Industrie grosse Hoffnungen in die semantischen Beschreibung von Web Services zur weitgehenden Automatisierung dieser Aufgaben.

[Pol06] Axel Polleres. Logic programs with contextually scoped negation. In 20th Workshop on Logic Programming (WLP 2006), Vienna, Austria, February 2006. [ .pdf ]
The Semantic Web community is currently dominated by knowledge representation formalisms adhering to a strict open world assumption. Nonmonotonic reasoning formalisms are viewed with partial scepticism and it is often argued that nonmonotonic reasoning techniques which adopt a closed world assumption are invalid in an open environment such as the Web where knowledge is notoriously incomplete. Nonetheless, in the ongoing discussion about rule extensions for Semantic Web Languages like RDF(S) or OWL several proposals have been made to partly break with this view and to allow a restricted form of negation as failure. Recently, the term “scoped negation” emerged in discussions around this topic, yet a clear definition about the meaning of “scope” and “scoped negation” and a formal semantics are still missing. In this paper we provide preliminary results towards these missing definitions and define two possible semantics for logic programs with contextually scoped negation, which we propose as an extension of RDFS.

[FLP+06] Dieter Fensel, Holger Lausen, Axel Polleres, Jos de Bruijn, Michael Stollberg, Dumitru Roman, and John Domingue. Enabling Semantic Web Services : The Web Service Modeling Ontology. Springer, 2006. [ http ]
The goal of this book is to provide an insight into and an understanding of the problems faced by Web services and service-oriented architectures, as well as the promises and solutions of the Semantic Web. We focus particularly on the Web Service Modeling Ontology (WSMO), which provides a comprehensive conceptual framework for the fruitful combination of Semantic Web technologies and Web services. With the present book we want to give an overall understanding of the WSMO framework and show how it can be applied to the problems of service-oriented architectures. It is not a ready-to-install “user manual” for Semantic Web services that is provided with this book, but rather an in-depth introduction. While many of the related technologies and standards are still under development we nevertheless think it is not too early for such a book: it is important to create an awareness of this technology and think about it today rather than tomorrow. The technology might not be at an industrial strength maturity yet, but the problems are already.

[EP06] Thomas Eiter and Axel Polleres. Towards automated integration of guess and check programs in answer set programming: A meta-interpreter and applications. Theory and Practice of Logic Programming (TPLP), 6(1-2):23-60, 2006. [ http ]
Answer set programming (ASP) with disjunction offers a powerful tool for declaratively representing and solving hard problems. Many NP-complete problems can be encoded in the answer set semantics of logic programs in a very concise and intuitive way, where the encoding reflects the typical “guess and check” nature of NP problems: The property is encoded in a way such that polynomial size certificates for it correspond to stable models of a program. However, the problem-solving capacity of full disjunctive logic programs (DLPs) is beyond NP, and captures a class of problems at the second level of the polynomial hierarchy. While these problems also have a clear “guess and check” structure, finding an encoding in a DLP reflecting this structure may sometimes be a non-obvious task, in particular if the “check” itself is a coNP-complete problem; usually, such problems are solved by interleaving separate guess and check programs, where the check is expressed by inconsistency of the check program. In this paper, we present general transformations of head-cycle free (extended) disjunctive logic programs into stratified and positive (extended) disjunctive logic programs based on meta-interpretation techniques. The answer sets of the original and the transformed program are in simple correspondence, and, moreover, inconsistency of the original program is indicated by a designated answer set of the transformed program. Our transformations facilitate the integration of separate “guess” and “check” programs, which are often easy to obtain, automatically into a single disjunctive logic program. Our results complement recent results on meta-interpretation in ASP, and extend methods and techniques for a declarative “guess and check” problem solving paradigm through ASP.


2005


[HPvHG05] Martin Hepp, Axel Polleres, Frank van Harmelen, and Michael R. Genesereth, editors. Proceedings of the First International Workshop on Mediation in Semantic Web Services (MEDIATE 2005), volume 168 of CEUR Workshop Proceedings, Amsterdam, The Netherlands, December 2005. CEUR-WS.org. [ http ]
Workshop Proceedings. This workshop was co-located with ICSOC 2005.

[KHP+05] Reto Krummenacher, Martin Hepp, Axel Polleres, Christoph Bussler, and Dieter Fensel. WWW or What is Wrong with Web Services. In Welf Löwe and Jean-Philippe Martin-Flatin, editors, Proceedings of the 3rd European Conference on Web Services (ECOWS 2005), pages 235-243, Växjö, Sweden, November 2005. IEEE Computer Society. [ .pdf ]
A core paradigm of the Web is information exchange via persistent publication, i.e., one party publishes a piece of information on the Web, and any other party who knows the location of the resource can retrieve and process the information at any later point in time and without the need for synchronization with the original publisher. This functionality significantly contributed to the scalability of the Web, since it reduced the amount of interaction between the sender and receiver. Current approaches of extending the World Wide Web from a collection of human-readable information, connecting humans, into a network that connects computing devices based on machine-processable semantics of data lack this feature and are instead based on tightly-coupled message exchange. In this paper, we (1) show that Web services based on the message-exchange paradigm are not fully compliant with core paradigms of the Web itself, (2) outline how the idea of persistent publication as a communication paradigm can be beneficially applied to Web services, and (3) propose a minimal architecture for fully Web-enabled Semantic Web services based on publication in shared information spaces, which we call Triple Space Computing.

[ABdB+05] Jürgen Angele, Harold Boley, Jos de Bruijn, Dieter Fensel, Pascal Hitzler, Michael Kifer, Reto Krummenacher, Holger Lausen, Axel Polleres, and Rudi Studer. Web Rule Language (WRL), September 2005. W3C member submission. [ http ]
The Web Rule Language WRL is a rule-based ontology language for the Semantic Web. The language is located in the Semantic Web stack next to the Description Logic based Ontology language OWL. WRL defines three variants, namely Core, Flight and Full. The Core variant marks the common fragment between WRL and OWL. WRL-Flight is a Datalog-based rule language. WRL-Full is a full-fledged rule language with function symbols and negation under the Well-Founded Semantics.

[FDP+05] Cristina Feier, Roman Dumitru, Axel Polleres, John Domingue, Michael Stollberg, and Dieter Fensel. Towards intelligent web services: The web service modeling ontology (WSMO). In Proceedings of the 2005 International Conference on Intelligent Computing (ICIC'05), Hefei, China, August 2005. [ .pdf ]
The Semantic Web and Semantic Web Services build a natural application area for Intelligent Agents, namely querying and reasoning about structured knowledge and semantic descriptions of services and their interfaces on the Web. This paper provides an overview of the Web Service Modeling Ontology, a conceptual framework for the semantical description of Web services.

[dBBD+05] Jos de Bruijn, Christoph Bussler, John Domingue, Dieter Fensel, Martin Hepp, Uwe Keller, Michael Kifer, Birgitta König-Ries, Jacek Kopecky, Rubén Lara, Holger Lausen, Eyal Oren, Axel Polleres, Dumitru Roman, James Scicluna, and Michael Stollberg. Web Service Modeling Ontology (WSMO), June 2005. W3C member submission. [ http ]
The potential to achieve dynamic, scalable and cost-effective infrastructure for electronic transactions in business and public administration has driven recent research efforts towards so-called Semantic Web services, that is enriching Web services with machine-processable semantics. Supporting this goal, the Web Service Modeling Ontology (WSMO) provides a conceptual framework and a formal language for semantically describing all relevant aspects of Web services in order to facilitate the automation of discovering, combining and invoking electronic services over the Web. This document describes the overall structure of WSMO by its four main elements: ontologies, which provide the terminology used by other WSMO elements, Web service descriptions, which describe the functional and behavioral aspects of a Web service, goals that represent user desires, and mediators, which aim at automatically handling interoperability problems between different WSMO elements. Along with introducing the main elements of WSMO, the syntax of the formal logic language used in WSMO is provided. The semantics and computationally tractable subsets of this logical language are defined and discussed in a separate document of the submission, the Web Service Modeling Language (WSML) document.

[dBFK+05] Jos de Bruijn, Dieter Fensel, Uwe Keller, Michael Kifer, Reto Krummenacher, Holger Lausen, Axel Polleres, and Livia Predoiu. Web Service Modeling Language (WSML), June 2005. W3C member submission. [ http ]
In this document, we introduce the Web Service Modeling Language WSML which provides a formal syntax and semantics for the Web Service Modeling Ontology WSMO. WSML is based on different logical formalisms, namely, Description Logics, First-Order Logic and Logic Programming, which are useful for the modeling of Semantic Web services. WSML consists of a number of variants based on these different logical formalisms, namely WSML-Core, WSML-DL, WSML-Flight, WSML-Rule and WSML-Full. WSML-Core corresponds with the intersection of Description Logic and Horn Logic. The other WSML variants provide increasing expressiveness in the direction of Description Logics and Logic Programming. Finally, both paradigms are unified in WSML-Full, the most expressive WSML variant. WSML is specified in terms of a normative human-readable syntax. Besides the human-readable syntax, WSML has an XML and an RDF syntax for exchange over the Web and for interoperation with RDF-based applications. Furthermore, we provide a mapping between WSML ontologies and OWL ontologies for interoperation with OWL ontologies through a common semantic subset of OWL and WSML.

[FKL+05] Dieter Fensel, Uwe Keller, Holger Lausen, Axel Polleres, and Ioan Toma. What is wrong with Web service discovery. In W3C Workshop on Frameworks for Semantics in Web Services, Innsbruck, Austria, June 2005. [ .pdf ]
[PTF05] Axel Polleres, Ioan Toma, and Dieter Fensel. Modeling services for the semantic grid. In The Dagstuhl Seminar 05271 - Semantic Grid: The Convergence of Technologies, May 2005. Extended Abstract. [ http ]
The Grid has emerged as a new distributed computing infrastructure for advanced science and engineering aiming at enabling sharing of resources and information towards coordinated problem solving in dynamic environments. Research in Grid Computing and Web Services has recently converged in what is known as the Web Service Resource Framework. While Web Service technologies and standards such as SOAP and WSDL provide the syntactical basis for communication in this framework, a service oriented grid architecture for communication has been defined in the Open Grid Service architecture. Wide agreement that a flexible service Grid is not possible without support by Semantic technologies has lead to the term “Semantic Grid” which is at the moment only vaguely defined. In our ongoing work on the Web Service Modeling Ontology (WSMO) we so far concentrated on the semantic description of Web services with respect to applications in Enterprise Application Integration and B2B integration scenarios. Although the typical application areas of Semantic Web services have slightly different requirements than the typical application scenarios in the Grid a big overlap justifies the assumption that most research results in the Semantic Web Services area can be similarly applied in the Semantic Grid. The present abstract summarizes the authors view on how to fruitfully integrate Semantic Web service technologies around WSMO/WSML and WSMX and Grid technologies in a Semantic Service Grid and gives an outlook on further possible directions and research. The reminder of this abstract is structured as follows. After giving a short overview of the current Grid Service architecture and its particular requirements, we shortly review the basic usage tasks for Semantic Web services. We then point out how these crucial tasks of Semantic Web services are to be addressed by WSMO. In turn, we try to analyze which special requirements for Semantic Web Services arise with respect to the Grid. We conclude by giving an outlook on the limitations of current Semantic Web services technologies and how we plan to address these in the future in a common Framework for Semantic Grid services.

[KLL+05] Uwe Keller, Rubén Lara, Holger Lausen, Axel Polleres, and Dieter Fensel. Automatic location of services. In Proceedings of the 2nd European Semantic Web Conference (ESWC2005), May 2005. [ .pdf ]
The automatic location of services that fulfill a given need is seen as a key step towards dynamic and scalable integration. In this paper we present a model for the automatic location of services that considers the static and dynamic aspects of service descriptions and identifies what notions of match and techniques are useful for the matching of both. Our model presents three important features: ease of use for the requester, efficient pre-filtering of relevant services, and accurate contracting of services that fulfill a given requester goal. We further elaborate previous work and results on Web service discovery by analyzing what steps and what kind of descriptions are necessary for an efficient and usable automatic service location. Furthermore, we analyze the intuitive and formal notions of match that are of interest for locating services that fulfill a given goal. Although having a formal underpinning, the proposed model does not impose any restrictions on how to implement it for specific applications, but proposes some useful formalisms for providing such implementation.

[BPLF05] Jos De Bruijn, Axel Polleres, Rubén Lara, and Dieter Fensel. OWL DL vs. OWL Flight: Conceptual modeling and reasoning for the semantic web. In Proceedings of the 14th World Wide Web Conference (WWW2005), pages 623-632, Chiba, Japan, May 2005. ACM Press. [ .pdf ]
The Semantic Web languages RDFS and OWL have been around for some time now. However, the presence of these languages has not brought the breakthrough of the Semantic Web the creators of the languages had hoped for. OWL has a number of problems in the area of interoperability and usability in the context of many practical application scenarios which impede the connection to the Software Engineering and Database communities. In this paper we present OWL Flight, which is loosely based on OWL, but the semantics is grounded in Logic Programming rather than Description Logics, and it borrows the constraint-based modeling style common in databases. This results in different types of modeling primitives and enforces a different style of ontology modeling. We analyze the modeling paradigms of OWL DL and OWL Flight, as well as reasoning tasks supported by both languages. We argue that different applications on the Semantic Web require different styles of modeling and thus both types of languages are required for the Semantic Web.

[Pol05] Axel Polleres. Semantic web languages and semantic web services as application areas for answer set programming. In The Dagstuhl Seminar 05171 - Nonmonotonic Reasoning, Answer Set Programming and Constraints, May 2005. Extended Abstract. [ http ]
In the Semantic Web and Semantic Web Services areas there are still unclear issues concerning an appropriate language. Answer Set Programming and ASP engines can be particularly interesting for Ontological Reasoning, especially in the light of ongoing discussions of non-monotonic extensions for Ontology Languages. Previously, the main concern of discussions was around OWL and Description Logics. Recently many extensions and suggestions for Rule Languages and Semantic Web Languages pop up, particularly in the the context of Semantic Web Services, which involve the meta-data description of Services instaead of static data on the Web only. These lanuages involve SWRL, WSML, SWSL-Rules, etc. I want to give an outline of languages, challenges and initiatives in this area and where I think Answer Set Programming research can hook in.

[LdBPF05] Holger Lausen, Jos de Bruijn, Axel Polleres, and Dieter Fensel. WSML - a language framework for semantic web services. In W3C Workshop on Rule Languages for Interoperability, Washington, D.C., USA, April 2005. [ http ]
The Web Service Modeling Language (WSML) provides a framework of different language variants to describe semantic Web services. This paper presents the design rationale and relation with existing language recommendations. WSML is a frame based language with an intuitive human readable syntax and XML and RDF exchange syntaxes, as well as a mapping to OWL. It provides different variants, allowing for open and closed world modeling; it is a fully-fledged ontology and rule language with defined variants grounded in well known formalisms, namely Datalog, Description Logic and Frame Logic. Taking the key aspects of WSML as a starting point, we rationalize the design decisions which we consider relevant in designing a proper layering of ontology and rule languages for the Semantic Web and semantic Web services.

[dBLPF05] Jos de Bruijn, Holger Lausen, Axel Polleres, and Dieter Fensel. The WSML rule languages for the semantic web. In W3C Workshop on Rule Languages for Interoperability, Washington, D.C., USA, April 2005. [ http ]
The Web Service Modeling Language WSML provides a framework for the modeling of ontologies and semantic Web services based on the conceptual model of the Web Service Modeling Ontology. In this paper we describe the two rule-based WSML-variants and outline our position with respect to a rule language for the Semantic Web. The first rule-based WSML variant, WSML-Flight, semantically corresponds to the Datalog fragment of F-Logic, extended with inequality in the body and locally stratified negation under the Perfect model semantics. The second, WSML-Rule, is an extension of WSML-Flight to the logic programming subset of F-Logic which allows the use of function symbols and unsafe rules (i.e., there may be variables in rule heads which do not occur in the body).

[SP05] James Scicluna and Axel Polleres. Semantic web service execution for WSMO based choreographies. In Workshop on Semantic Web Applications at the 11th EUROMEDIA Conference, Toulouse, France, April 2005. [ .pdf ]
The Semantic Web is slowly gathering more importance as both academic and industrial organizations are realizing the potential benefit that might be obtained from it. This is especially true in the areas of tourism in which Semantic Web Services can provide a drastically new way on how to find and book related services such as hotel, flights and taxi transfers. However, many aspects of Semantic Web Services are still under development. This short paper presents issues related to choreography and orchestration representation in the Web Service Modelling Ontology (WSMO) and also how such ideas can be applied to an e-tourism use case.

[RKL+05] Dumitru Roman, Uwe Keller, Holger Lausen, Jos de Bruijn, Rubén Lara, Michael Stollberg, Axel Polleres, Cristina Feier, Cristoph Bussler, and Dieter Fensel. Web service modeling ontology. Applied Ontology, 2005. [ http ]
The potential to achieve dynamic, scalable and cost-effective marketplaces and eCommerce solutions has driven recent research efforts towards so-called Semantic Web Services that are enriching Web services with machine-processable semantics. To this end, the Web Service Modeling Ontology (WSMO) provides the conceptual underpinning and a formal language for semantically describing all relevant aspects of Web services in order to facilitate the automatization of discovering, combining and invoking electronic services over the Web. In this paper we describe the overall structure of WSMO by its four main elements: ontologies, which provide the terminology used by other WSMO elements, Web services, which provide access to services that, in turn, provide some value in some domain, goals that represent user desires, and mediators, which deal with interoperability problems between different WSMO elements. Along with introducing the main elements of WSMO, we provide a logical language for defining formal statements in WSMO together with some motivating examples from practical use cases which shall demonstrate the benefits of Semantic Web Services.


2004


[BPLF04] Jos De Bruijn, Axel Polleres, Rubén Lara, and Dieter Fensel. OWL DL vs. OWL Flight: Conceptual modeling and reasoning for the semantic web. Technical Report DERI-TR-2004-11-10, Digital Enterprise Research Institute (DERI), November 2004. [ .pdf ]
[KLP+04] Michael Kifer, Rubén Lara, Axel Polleres, Chang Zhao, Uwe Keller, Holger Lausen, and Dieter Fensel. A logical framework for web service discovery. In ISWC 2004 Workshop on Semantic Web Services: Preparing to Meet the World of Business Applications, Hiroshima, Japan, November 2004. [ .pdf ]
[ABK+04] Sinuhé Arroyo, Christoph Bussler, Jacek Kopecký, Rubén Lara, Axel Polleres, and Michal Zaremba. Web service capabilities and constraints in WSMO. In W3C Workshop on Constraints and Capabilities for Web Services, Oracle Conference Center, Redwood Shores, CA, USA, October 2004. [ .html ]
[LRPF04] Rubén Lara, Dumitru Roman, Axel Polleres, and Dieter Fensel. A conceptual comparison of WSMO and OWL-S. In Proceedings of the European Conference on Web Services (ECOWS 2004), volume 3250 of Lecture Notes in Computer Science (LNCS), pages 254-269, Erfurt, Germany, September 2004. [ http ]
[OLPL04] Daniel Olmedilla, Rubén Lara, Axel Polleres, and Holger Lausen. Trust negotiation for semantic web services. In Proceedings of the First International Workshop on Semantic Web Services and Web Process Composition (SWSWPC 2004), San Diego, California, USA, July 2004. [ .pdf ]
[BP04] Jos De Bruijn and Axel Polleres. Towards an ontology mapping specification language for the semantic web. Technical Report DERI-TR-2004-06-30, Digital Enterprise Research Institute (DERI), June 2004. [ .pdf ]
[EFL+04] Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, and Axel Polleres. A Logic Programming Approach to Knowledge-State Planning: Semantics and Complexity. ACM Transactions on Computational Logic, 5(2):206-263, April 2004. [ http ]
[EFPP04] Thomas Eiter, Wolfgang Faber, Gerald Pfeifer, and Axel Polleres. Declarative planning and knowledge representation in an action language. In Ioannis Vlahavas and Dimitris Vrakas, editors, Intelligent Techniques for Planning. IDEA Group Publishing, 2004. [ http ]
This chapter introduces planning and knowledge representation in the declarative action language K. Rooted in the area of Knowledge Representation & Reasoning, action languages like K allow the formalization of complex planning problems involving non-determinism and incomplete knowledge in a very flexible manner. By giving an overview of existing planning languages and comparing these against our language, we aim on further promoting the applicability and usefulness of high-level action languages in the area of planning. As opposed to previously existing languages for modeling actions and change, K adopts a logic programming view where fluents representing the epistemic state of an agent might be true, false or undefined in each state. We will show that this view of knowledge states can be fruitfully applied to several well-known planning domains from the literature as well as novel planning domains. Remarkably, K often allows to model problems more concisely than previous action languages. All the examples given can be tested in an available implementation, the DLVK planning system.

[EP04] Thomas Eiter and Axel Polleres. Towards automated integration of guess and check programs in answer set programming. In Vladimir Lifschitz and Ilkka Niemelä, editors, Proceedings of the Seventh International Conference on Logic Programming and Nonmonotonic Reasoning (LPNMR-7), number 2923 in Lecture Notes in AI (LNAI), pages 100-113, Fort Lauderdale, Florida, USA, January 2004. Springer. [ http ]

2003


[DEF+03b] Jürgen Dix, Thomas Eiter, Michael Fink, Axel Polleres, and Yingqian Zhang. Monitoring Agents using Declarative Planning. Fundamenta Informaticae, 57(2):345-370, November 2003. [ .ps.gz ]
[EP03] Thomas Eiter and Axel Polleres. Transforming coNP checks to answer set computation by meta-interpretation. In Proceedings of the 2003 Joint Conference on Declarative Programming APPIA-GULP-PRODE 2003, Reggio Calabria, Italy, September 2003. [ .pdf ]
[Pol03a] Axel Polleres. Advances in Answer Set Planning. thesis, Institut für Informationssysteme, Technische Universität Wien, Wien, Österreich, September 2003. [ .pdf ]
[DEF+03a] Jürgen Dix, Thomas Eiter, Michael Fink, Axel Polleres, and Yingqian Zhang. Monitoring Agents using Declarative Planning. In Proceedings of the 26th German Conference on Artificial Intelligence (KI2003), volume 2821 of Lecture Notes in Computer Science (LNCS), pages 646-660. Springer, September 2003. [ .pdf ]
[Pol03b] Axel Polleres. The declarative planning system DLVK: Progress and extensions. In Jeremy Frank and Susanne Biundo, editors, Printed Notes of the ICAPS-03 Doctoral Consortium, pages 94-98, June 2003. [ .pdf ]
[EFL+03a] Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, and Axel Polleres. A Logic Programming Approach to Knowledge-State Planning, II: the DLVK System. Artificial Intelligence, 144(1-2):157-211, March 2003. [ .ps.gz ]
[EFL+03b] Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, and Axel Polleres. Answer Set Planning under Action Costs. Journal of Artificial Intelligence Research (JAIR), 19:25-71, 2003. [ .ps ]

2002


[EFL+02b] Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, and Axel Polleres. Answer Set Planning under Action Costs. Technical Report INFSYS RR-1843-02-13, Institut für Informationssysteme, Technische Universität Wien, October 2002. Published in Journal of Artificial Intelligence Research. [ .ps.gz ]
[EFL+02a] Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, and Axel Polleres. Answer Set Planning under Action Costs. In Sergio Flesca, Sergio Greco, Giovambattista Ianni, and Nicola Leone, editors, Proceedings of the 8th European Conference on Artificial Intelligence (JELIA), volume 2424 of Lecture Notes in Computer Science (LNCS), pages 186-197, Cosenza, Italy, September 2002. [ http ]
[EFL+02c] Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, and Axel Polleres. The DLVK Planning System: Progress Report. In Sergio Flesca, Sergio Greco, Giovambattista Ianni, and Nicola Leone, editors, Proceedings of the 8th European Conference on Artificial Intelligence (JELIA), volume 2424 of Lecture Notes in Computer Science (LNCS), pages 541-544, Cosenza, Italy, September 2002. (System Description). [ http ]
[LPF+02] Nicola Leone, Gerald Pfeifer, Wolfgang Faber, Francesco Calimeri, Tina Dell'Armi, Thomas Eiter, Georg Gottlob, Giovambattista Ianni, Giuseppe Ielpa, Christoph Koch, Simona Perri, and Axel Polleres. The DLV System. In Sergio Flesca, Sergio Greco, Giovambattista Ianni, and Nicola Leone, editors, Proceedings of the 8th European Conference on Logics in Artificial Intelligence (JELIA), volume 2424 of Lecture Notes in Computer Science (LNCS), pages 537-540, Cosenza, Italy, September 2002. (System Description). [ http ]
[Pol02b] Axel Polleres. Answer Set Planning with DLVK: Planning with Action Costs, September 2002. Poster presented at the PLANET'02 International Summer School on AI Planning 2002. [ .pdf ]
[Pol02a] Axel Polleres. Answer Set Planning with DLVK. The PLANET Newsletter, 5:36-37, 2002. [ .pdf ]
[Pol02c] Axel Polleres. JELIA 2002. COMPUTER kommunikativ, 5/2002:28-29, 2002. Conference report.
[Pol02e] Axel Polleres. Planen in der AI. COMPUTER kommunikativ, 5/2002:30-31, 2002. Conference report.
[Pol02d] Axel Polleres. JELIA 2002. ÖGAI Journal, 21(4):23-25, 2002. Conference report.
[Pol02f] Axel Polleres. PLANET International Summer School on AI Planning 2002, Chalkidiki, Griechenland. ÖGAI Journal, 21(4):26-29, 2002. Conference report.

2001


[EFL+01b] Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, and Axel Polleres. A Logic Programming Approach to Knowledge-State Planning: Semantics and Complexity. Technical Report INFSYS RR-1843-01-11, Institut für Informationssysteme, Technische Universität Wien, December 2001. [ .ps.gz ]
[EFL+01a] Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, and Axel Polleres. A Logic Programming Approach to Knowledge-State Planning, II: the DLVK System. Technical Report INFSYS RR-1843-01-12, Institut für Informationssysteme, Technische Universität Wien, December 2001. [ .ps.gz ]
[EFL+01c] Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, and Axel Polleres. System Description: The DLVK Planning System. In Thomas Eiter, Wolfgang Faber, and Miroslaw Truszczyński, editors, Logic Programming and Nonmonotonic Reasoning - 6th International Conference, LPNMR'01, Vienna, Austria, September 2001, Proceedings, number 2173 in Lecture Notes in AI (LNAI), pages 413-416. Springer Verlag, September 2001. [ .ps.gz ]
[EFL+01d] Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, and Axel Polleres. The DLVK Planning System. In Alessandro Cimatti, Héctor Geffner, Enrico Giunchiglia, and Jussi Rintanen, editors, IJCAI-01 Workshop on Planning under Uncertainty and Incomplete Information, pages 76-81, August 2001.
[Pol01] Axel Polleres. The DLVK System for Planning with Incomplete Knowledge. thesis, Institut für Informationssysteme, Technische Universität Wien, Wien, Österreich, February 2001. [ .pdf ]

2000


[EFL+00a] Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, and Axel Polleres. Planning under Incomplete Knowledge. In John Lloyd, Veronica Dahl, Ulrich Furbach, Manfred Kerber, Kung-Kiu Lau, Catuscia Palamidessi, Luís Moniz Pereira, Yehoshua Sagiv, and Peter J. Stuckey, editors, Computational Logic - CL 2000, First International Conference, Proceedings, number 1861 in Lecture Notes in AI (LNAI), pages 807-821, London, UK, July 2000. Springer Verlag. [ .ps.gz ]
[EFL+00b] Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, and Axel Polleres. Using the dlv System for Planning and Diagnostic Reasoning. In François Bry, Ulrich Geske, and Dietmar Seipel, editors, Proceedings of the 14th Workshop on Logic Programming (WLP'99), pages 125-134. GMD - Forschungszentrum Informationstechnik GmbH, Berlin, January 2000. ISSN 1435-2702. [ .pdf ]

1999


[EFPT99] Uwe Egly, Michael Fink, Axel Polleres, and Hans Tompits. A web-based tutoring tool for calculating default logic extensions. In Proceedings of the World Conference on the WWW and Internet (WEBNET'99). AACE, 1999. [ .pdf ]

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