Axel Polleres

Olivier Boissier, Marco Colombetti, Michael Luck, John-Jules Meyer, Axel Polleres: Norms, organizations, and semantics. Knowledge Eng. Review 28(1): 107-116 (2013)

Carlos Buil Aranda, Marcelo Arenas, Óscar Corcho, Axel Polleres: Federating queries in SPARQL 1.1: Syntax, semantics and evaluation. J. Web Sem. 18(1): 1-17 (2013)

Javier D. Fernández, Miguel A. Martínez-Prieto, Claudio Gutiérrez, Axel Polleres, Mario Arias: Binary RDF representation for publication and exchange (HDT). J. Web Sem. 19: 22-41 (2013)

Stefan Bischof, Axel Polleres: RDFS with Attribute Equations via SPARQL Rewriting. ESWC 2013: 335-350

Stefan Bischof, Stefan Decker, Thomas Krennwallner, Nuno Lopes, Axel Polleres: Mapping between RDF and XML with XSPARQL. J. Data Semantics 1(3): 147-185 (2012)

Aidan Hogan, Antoine Zimmermann, Jürgen Umbrich, Axel Polleres, Stefan Decker: Scalable and distributed methods for entity matching, consolidation and disambiguation over linked data corpora. J. Web Sem. 10: 76-110 (2012)

Antoine Zimmermann, Nuno Lopes, Axel Polleres, Umberto Straccia: A general framework for representing, reasoning and querying with annotated Semantic Web data. J. Web Sem. 11: 72-95 (2012)

Aidan Hogan, Jürgen Umbrich, Andreas Harth, Richard Cyganiak, Axel Polleres, Stefan Decker: An empirical survey of Linked Data conformance. J. Web Sem. 14: 14-44 (2012)

Axel Polleres: How (Well) Do Datalog, SPARQL and RIF Interplay? Datalog 2012: 27-30

Jürgen Umbrich, Marcel Karnstedt, Josiane Xavier Parreira, Axel Polleres, Manfred Hauswirth: Linked Data and Live Querying for Enabling Support Platforms for Web Dataspaces. ICDE Workshops 2012: 23-28

Nuno Lopes, Sabrina Kirrane, Antoine Zimmermann, Axel Polleres, Alessandra Mileo: A Logic Programming approach for Access Control over RDF. ICLP (Technical Communications) 2012: 381-392

Jürgen Umbrich, Aidan Hogan, Axel Polleres, Stefan Decker: Improving the Recall of Live Linked Data Querying through Reasoning. RR 2012: 188-204

Anna Ryabokon, Axel Polleres, Gerhard Friedrich, Andreas A. Falkner, Alois Haselböck, Herwig Schreiner: (Re)Configuration Using Web Data: A Case Study on the Reviewer Assignment Problem. RR 2012: 258-261

Birte Glimm, Aidan Hogan, Markus Krötzsch, Axel Polleres: OWL: Yet to arrive on the Web of Data? LDOW 2012

Tobias Käfer, Jürgen Umbrich, Aidan Hogan, Axel Polleres: DyLDO: Towards a Dynamic Linked Data Observatory. LDOW 2012

Elena Simperl, Philipp Cimiano, Axel Polleres, Óscar Corcho, Valentina Presutti (Eds.): The Semantic Web: Research and Applications - 9th Extended Semantic Web Conference, ESWC 2012, Heraklion, Crete, Greece, May 27-31, 2012. Proceedings. Lecture Notes in Computer Science 7295, Springer 2012, isbn 978-3-642-30283-1

Birte Glimm, Aidan Hogan, Markus Krötzsch, Axel Polleres: OWL: Yet to arrive on the Web of Data? CoRR abs/1202.0984 (2012)

Jos de Bruijn, Thomas Eiter, Axel Polleres, Hans Tompits: Embedding nonground logic programs into autoepistemic logic for knowledge-base combination. ACM Trans. Comput. Log. 12(3): 20 (2011)

Piero A. Bonatti, Aidan Hogan, Axel Polleres, Luigi Sauro: Robust and scalable Linked Data reasoning incorporating provenance and trust annotations. J. Web Sem. 9(2): 165-201 (2011)

Aidan Hogan, Andreas Harth, Jürgen Umbrich, Sheila Kinsella, Axel Polleres, Stefan Decker: Searching and browsing Linked Data with SWSE: The Semantic Web Search Engine. J. Web Sem. 9(4): 365-401 (2011)

Jürgen Umbrich, Katja Hose, Marcel Karnstedt, Andreas Harth, Axel Polleres: Comparing data summaries for processing live queries over Linked Data. World Wide Web 14(5-6): 495-544 (2011)

Ratnesh Sahay, Ronan Fox, Antoine Zimmermann, Axel Polleres, Manfred Hauswirth: A Methodological Approach for Ontologising and Aligning Health Level Seven (HL7) Applications. ARES 2011: 102-117

Anca Dumitrache, Alessandra Mileo, Antoine Zimmermann, Axel Polleres, Philipp Obermeier, Owen Friel: Enabling Privacy-Preserving Semantic Presence in Instant Messaging Systems. CONTEXT 2011: 82-96

Renaud Delbru, Giovanni Tummarello, Axel Polleres: Context-Dependent OWL Reasoning in Sindice - Experiences and Lessons Learnt. RR 2011: 46-60

Stefan Bischof, Nuno Lopes, Axel Polleres: Improve Efficiency of Mapping Data between XML and RDF with XSPARQL. RR 2011: 232-237

Aidan Hogan, Jeff Z. Pan, Axel Polleres, Yuan Ren: Scalable OWL 2 Reasoning for Linked Data. Reasoning Web 2011: 250-325

Alejandro Mallea, Marcelo Arenas, Aidan Hogan, Axel Polleres: On Blank Nodes. International Semantic Web Conference (1) 2011: 421-437

Axel Polleres, Claudia d'Amato, Marcelo Arenas, Siegfried Handschuh, Paula Kroner, Sascha Ossowski, Peter F. Patel-Schneider (Eds.): Reasoning Web. Semantic Technologies for the Web of Data - 7th International Summer School 2011, Galway, Ireland, August 23-27, 2011, Tutorial Lectures. Lecture Notes in Computer Science 6848, Springer 2011, isbn 978-3-642-23031-8

Antoine Zimmermann, Nuno Lopes, Axel Polleres, Umberto Straccia: A General Framework for Representing, Reasoning and Querying with Annotated Semantic Web Data. CoRR abs/1103.1255 (2011)

Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, Axel Polleres: Answer Set Planning Under Action Costs. CoRR abs/1106.5257 (2011)

Jürgen Umbrich, Aidan Hogan, Axel Polleres: Improving the recall of decentralised linked data querying through implicit knowledge. CoRR abs/1109.0181 (2011)

Jos de Bruijn, David Pearce, Axel Polleres, Agustín Valverde: A semantical framework for hybrid knowledge bases. Knowl. Inf. Syst. 25(1): 81-104 (2010)

Axel Polleres, Aidan Hogan, Andreas Harth, Stefan Decker: Can we ever catch up with the Web? Semantic Web 1(1-2): 45-52 (2010)

Umberto Straccia, Nuno Lopes, Gergely Lukacsy, Axel Polleres: A General Framework for Representing and Reasoning with Annotated Semantic Web Data. AAAI 2010

Reinhard Pichler, Axel Polleres, Sebastian Skritek, Stefan Woltran: Minimising RDF Graphs under Rules and Constraints Revisited. AMW 2010

Manfred Hauswirth, Jérôme Euzenat, Owen Friel, K. Griffin, P. Hession, B. Jennings, Tudor Groza, Siegfried Handschuh, Ivana Podnar Zarko, Axel Polleres, Antoine Zimmermann: Towards Consolidated Presence. CollaborateCom 2010: 1-10

Maria-Esther Vidal, Edna Ruckhaus, Tomas Lampo, Amadís Martínez, Javier Sierra, Axel Polleres: Efficiently Joining Group Patterns in SPARQL Queries. ESWC (1) 2010: 228-242

Axel Polleres: SPARQL1.1: New Features and Friends (OWL2, RIF). RR 2010: 23-26

Reinhard Pichler, Axel Polleres, Sebastian Skritek, Stefan Woltran: Redundancy Elimination on RDF Graphs in the Presence of Rules, Constraints, and Queries. RR 2010: 133-148

Marco Marano, Philipp Obermeier, Axel Polleres: Processing RIF and OWL2RL within DLVHEX. RR 2010: 244-250

Aidan Hogan, Jeff Z. Pan, Axel Polleres, Stefan Decker: SAOR: Template Rule Optimisations for Distributed Reasoning over 1 Billion Linked Data Triples. International Semantic Web Conference (1) 2010: 337-353

Nuno Lopes, Axel Polleres, Umberto Straccia, Antoine Zimmermann: AnQL: SPARQLing Up Annotated RDFS. International Semantic Web Conference (1) 2010: 518-533

Andreas Harth, Katja Hose, Marcel Karnstedt, Axel Polleres, Kai-Uwe Sattler, Jürgen Umbrich: Data summaries for on-demand queries over linked data. WWW 2010: 411-420

Aidan Hogan, Andreas Harth, Alexandre Passant, Stefan Decker, Axel Polleres: Weaving the Pedantic Web. LDOW 2010

Jürgen Umbrich, Michael Hausenblas, Aidan Hogan, Axel Polleres, Stefan Decker: Towards Dataset Dynamics: Change Frequency of Linked Open Data Sources. LDOW 2010

Julian A. Padget, Alexander Artikis, Wamberto Weber Vasconcelos, Kostas Stathis, Viviane Torres da Silva, Eric T. Matson, Axel Polleres (Eds.): Coordination, Organizations, Institutions and Norms in Agent Systems V, 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. Lecture Notes in Computer Science 6069, Springer 2010, isbn 978-3-642-14961.0

Axel Polleres, Huajun Chen (Eds.): Proceedings of the ISWC 2010 Posters & Demonstrations Track: Collected Abstracts, Shanghai, China, November 9, 2010. CEUR Workshop Proceedings 658, CEUR-WS.org 2010

Aidan Hogan, Andreas Harth, Axel Polleres: Scalable Authoritative OWL Reasoning for the Web. Int. J. Semantic Web Inf. Syst. 5(2): 49-90 (2009)

Axel Polleres, David Huynh: Special issue: The Web of Data. J. Web Sem. 7(3): 135 (2009)

Giovambattista Ianni, Thomas Krennwallner, Alessandra Martello, Axel Polleres: A Rule System for Querying Persistent RDFS Data. ESWC 2009: 857-862

Julian A. Padget, Axel Polleres: Introductory Essay of COIN@MALLOW'009. MALLOW 2009

Antoine Zimmermann, Ratnesh Sahay, Ronan Fox, Axel Polleres: Heterogeneity and Context in Semantic-Web-Enabled HCLS Systems. OTM Conferences (2) 2009: 1165-1182

Giovambattista Ianni, Thomas Krennwallner, Alessandra Martello, Axel Polleres: Dynamic Querying of Mass-Storage RDF Data with Rule-Based Entailment Regimes. International Semantic Web Conference 2009: 310-327

Stephane Corlosquet, Renaud Delbru, Tim Clark, Axel Polleres, Stefan Decker: Produce and Consume Linked Data with Drupal! International Semantic Web Conference 2009: 763-778

Danh Le Phuoc, Axel Polleres, Manfred Hauswirth, Giovanni Tummarello, Christian Morbidoni: Rapid prototyping of semantic mash-ups through semantic web pipes. WWW 2009: 581-590

Axel Polleres, Malgorzata Mochol: Expertise bewerben und finden im Social Semantic Web. Social Semantic Web 2009: 175-206

Matteo Baldoni, Cristina Baroglio, Jamal Bentahar, Guido Boella, Massimo Cossentino, Mehdi Dastani, Barbara Dunin-Keplicz, Giancarlo Fortino, Marie Pierre Gleizes, João Leite, Viviana Mascardi, Julian A. Padget, Juan Pavón, Axel Polleres, Amal El Fallah-Seghrouchni, Paolo Torroni, Rineke Verbrugge (Eds.): Proceedings of the Second Multi-Agent Logics, Languages, and Organisations Federated Workshops, Turin, Italy, September 7-10, 2009. CEUR Workshop Proceedings 494, CEUR-WS.org 2009

Axel Polleres, Terrance Swift (Eds.): Web Reasoning and Rule Systems, Third International Conference, RR 2009, Chantilly, VA, USA, October 25-26, 2009, Proceedings. Lecture Notes in Computer Science 5837, Springer 2009, isbn 978-3-642-05081-7

Monika Lanzenberger, Jennifer Sampson, Horst Kargl, Manuel Wimmer, Colm Conroy, Declan O'Sullivan, David Lewis, Rob Brennan, José Ángel Ramos Gargantilla, Asunción Gómez-Pérez, Frédéric Fürst, Francky Trichet, Jérôme Euzenat, Axel Polleres, François Scharffe, Konstantinos Kotis: Making Ontologies Talk: Knowledge Interoperability in the Semantic Web. IEEE Intelligent Systems 23(6): 72-85 (2008)

Aidan Hogan, Andreas Harth, Axel Polleres: SAOR: Authoritative Reasoning for the Web. ASWC 2008: 76-90

Jérôme Euzenat, Axel Polleres, François Scharffe: Processing Ontology Alignments with SPARQL. CISIS 2008: 913-917

Reinhard Pichler, Axel Polleres, Fang Wei, Stefan Woltran: dRDF: Entailment for Domain-Restricted RDF. ESWC 2008: 200-214

Waseem Akhtar, Jacek Kopecký, Thomas Krennwallner, Axel Polleres: XSPARQL: Traveling between the XML and RDF Worlds - and Avoiding the XSLT Pilgrimage. ESWC 2008: 432-447

Christian Morbidoni, Danh Le Phuoc, Axel Polleres, Matthias Samwald, Giovanni Tummarello: Previewing Semantic Web Pipes. ESWC 2008: 843-848

Thomas Eiter, Giovambattista Ianni, Thomas Krennwallner, Axel Polleres: Rules and Ontologies for the Semantic Web. Reasoning Web 2008: 1-53

Hong Linh Truong, Schahram Dustdar, Dino Baggio, Stephane Corlosquet, Christoph Dorn, Giovanni Giuliani, Robert Gombotz, Yi Hong, Pete Kendal, Christian Melchiorre, Sarit Moretzky, Sebastien Peray, Axel Polleres, Stephan Reiff-Marganiec, Daniel Schall, Simona Stringa, Marcel Tilly, HongQing Yu: inContext: A Pervasive and Collaborative Working Environment for Emerging Team Forms. SAINT 2008: 118-125

Alberto Fernández, Conor Hayes, Nikos Loutas, Vassilios Peristeras, Axel Polleres, Konstantinos A. Tarabanis: Closing the Service Discovery Gap by Collaborative Tagging and Clustering Techniques. SMRR 2008

Matthias Klusch, Michal Pechoucek, Axel Polleres (Eds.): Cooperative Information Agents XII, 12th International Workshop, CIA 2008, Prague, Czech Republic, September 10-12, 2008. Proceedings. Lecture Notes in Computer Science 5180, Springer 2008, isbn 978-3-540-85833-1

Cristina Baroglio, Piero A. Bonatti, Jan Maluszynski, Massimo Marchiori, Axel Polleres, Sebastian Schaffert (Eds.): Reasoning Web, 4th International Summer School 2008, Venice, Italy, September 7-11, 2008, Tutorial Lectures. Lecture Notes in Computer Science 5224, Springer 2008, isbn 978-3-540-85656-6

Jos de Bruijn, Thomas Eiter, Axel Polleres, Hans Tompits: Embedding Non-Ground Logic Programs into Autoepistemic Logic for Knowledge Base Combination. CoRR abs/0811.0359 (2008)

Boanerges Aleman-Meza, Uldis Bojars, Harold Boley, John G. Breslin, Malgorzata Mochol, Lyndon J. B. Nixon, Axel Polleres, Anna V. Zhdanova: Combining RDF Vocabularies for Expert Finding. ESWC 2007: 235-250

Axel Polleres, Roman Schindlauer: DLVHEX-SPARQL: A SPARQL Compliant Query Engine Based on DLVHEX. ALPSWS 2007

Jos de Bruijn, Thomas Eiter, Axel Polleres, Hans Tompits: Embedding Non-Ground Logic Programs into Autoepistemic Logic for Knowledge-Base Combination. IJCAI 2007: 304-309

Axel Polleres, François Scharffe, Roman Schindlauer: SPARQL++ for Mapping Between RDF Vocabularies. OTM Conferences (1) 2007: 878-896

Jos de Bruijn, David Pearce, Axel Polleres, Agustín Valverde: Quantified Equilibrium Logic and Hybrid Rules. RR 2007: 58-72

Harold Boley, Michael Kifer, Paula-Lavinia Patranjan, Axel Polleres: Rule Interchange on the Web. Reasoning Web 2007: 269-309

Alberto Fernández, Axel Polleres, Sascha Ossowski: Towards Fine-grained Service Matchmaking by Using Concept Similarity. SMRR 2007

Christian Morbidoni, Axel Polleres, Giovanni Tummarello: Who the FOAF knows Alice? A Needed Step Toward Semantic Web Pipes. New Forms of Reasoning for the Semantic Web 2007

Christian Morbidoni, Axel Polleres, Giovanni Tummarello: Who the FOAF knows Alice? RDF Revocation in DBin 2.0. SWAP 2007

Axel Polleres: From SPARQL to rules (and back). WWW 2007: 787-796

Axel Polleres, David Pearce, Stijn Heymans, Edna Ruckhaus (Eds.): Proceedings of the ICLP'07 Workshop on Applications of Logic Programming to the Web, Semantic Web and Semantic Web Services, ALPSWS 2007, Porto, Portugal, September 13th, 2007. CEUR Workshop Proceedings 287, CEUR-WS.org 2007

David Pearce, Axel Polleres, Agustín Valverde, Stefan Woltran (Eds.): Proceedings of the LPNMR'07 Workshop on Correspondence and Equivalence for Nonmonotonic Theories (CENT2007), Tempe, AZ, May 14, 2007. CEUR Workshop Proceedings 265, CEUR-WS.org 2007

Tommaso Di Noia, Rubén Lara, Axel Polleres, Ioan Toma, Takahiro Kawamura, Matthias Klusch, Abraham Bernstein, Massimo Paolucci, Alain Leger, David L. Martin (Eds.): Proceedings of the SMR² 2007 Workshop on Service Matchmaking and Resource Retrieval in the Semantic Web (SMRR 2007) co-located with ISWC 2007 + ASWC 2007, Busan, South Korea, November 11, 2007. CEUR Workshop Proceedings 243, CEUR-WS.org 2007

Thomas Eiter, Axel Polleres: Towards automated integration of guess and check programs in answer set programming: a meta-interpreter and applications. TPLP 6(1-2): 23-60 (2006)

Axel Polleres, Cristina Feier, Andreas Harth: Rules with Contextually Scoped Negation. ESWC 2006: 332-347

Jos de Bruijn, Holger Lausen, Axel Polleres, Dieter Fensel: The Web Service Modeling Language WSML: An Overview. ESWC 2006: 590-604

Jos de Bruijn, Thomas Eiter, Axel Polleres, Hans Tompits: On Representational Issues About Combinations of Classical Theories with Nonmonotonic Rules. KSEM 2006: 1-22

Thomas Eiter, Giovambattista Ianni, Axel Polleres, Roman Schindlauer, Hans Tompits: Reasoning with Rules and Ontologies. Reasoning Web 2006: 93-127

Axel Polleres: Logic Programs with Contextually Scoped Negation. WLP 2006: 129-136

Dumitru Roman, Uwe Keller, Holger Lausen, Jos de Bruijn, Rubén Lara, Michael Stollberg, Axel Polleres, Cristina Feier, Christoph Bussler, Dieter Fensel: Web Service Modeling Ontology. Applied Ontology 1(1): 77-106 (2005)

Axel Polleres: Semantic Web Languages and Semantic Web Services as Application Areas for Answer Set Programming. Nonmonotonic Reasoning, Answer Set Programming and Constraints 2005

Axel Polleres, Ioan Toma, Dieter Fensel: Modeling Services for the Semantic Grid. Semantic Grid 2005

Uwe Keller, Rubén Lara, Holger Lausen, Axel Polleres, Dieter Fensel: Automatic Location of Services. ESWC 2005: 1-16

Reto Krummenacher, Martin Hepp, Axel Polleres, Christoph Bussler, Dieter Fensel: WWW or What Is Wrong with Web Services. ECOWS 2005: 235-243

Holger Lausen, Jos de Bruijn, Axel Polleres, Dieter Fensel: WSML - a Language Framework for Semantic Web Services. Rule Languages for Interoperability 2005

Holger Lausen, Jos de Bruijn, Axel Polleres, Dieter Fensel: The WSML Rule Languages for the Semantic Web. Rule Languages for Interoperability 2005

Jos de Bruijn, Rubén Lara, Axel Polleres, Dieter Fensel: OWL DL vs. OWL flight: conceptual modeling and reasoning for the semantic Web. WWW 2005: 623-632

Thomas Eiter, Axel Polleres: Towards Automated Integration of Guess and Check Programs in Answer Set Programming: A Meta-Interpreter and Applications. CoRR abs/cs/0501084 (2005)

Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, Axel Polleres: A logic programming approach to knowledge-state planning: Semantics and complexity. ACM Trans. Comput. Log. 5(2): 206-263 (2004)

Rubén Lara, Dumitru Roman, Axel Polleres, Dieter Fensel: A Conceptual Comparison of WSMO and OWL-S. ECOWS 2004: 254-269

Thomas Eiter, Axel Polleres: Towards Automated Integration of Guess and Check Programs in Answer Set Programming. LPNMR 2004: 100-113

Daniel Olmedilla, Rubén Lara, Axel Polleres, Holger Lausen: Trust Negotiation for Semantic Web Services. SWSWPC 2004: 81-95

Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, Axel Polleres: A logic programming approach to knowledge-state planning, II: The DLV^K system. Artif. Intell. 144(1-2): 157-211 (2003)

Jürgen Dix, Thomas Eiter, Michael Fink, Axel Polleres, Yingqian Zhang: Monitoring Agents using Declarative Planning. Fundam. Inform. 57(2-4): 345-370 (2003)

Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, Axel Polleres: Answer Set Planning Under Action Costs. J. Artif. Intell. Res. (JAIR) 19: 25-71 (2003)

Thomas Eiter, Axel Polleres: Transforming co-NP Checks to Answer Set Computation by Meta-Interpretation. APPIA-GULP-PRODE 2003: 410-421

Jürgen Dix, Thomas Eiter, Michael Fink, Axel Polleres, Yingqian Zhang: Monitoring Agents Using Declarative Planning. KI 2003: 646-660

Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, Axel Polleres: Answer Set Planning under Action Costs. JELIA 2002: 186-197

Nicola Leone, Gerald Pfeifer, Wolfgang Faber, Francesco Calimeri, Tina Dell'Armi, Thomas Eiter, Georg Gottlob, Giovambattista Ianni, Giuseppe Ielpa, Christoph Koch, Simona Perri, Axel Polleres: The DLV System. JELIA 2002: 537-540

Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, Axel Polleres: The DLV^K Planning System: Progress Report. JELIA 2002: 541-544

Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, Axel Polleres: System Description: The DLV^K Planning System. LPNMR 2001: 429-433

Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, Axel Polleres: A Logic Programming Approach to Knowledge-State Planning: Semantics and Complexity. CoRR cs.AI/0112006 (2001)

Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, Axel Polleres: Planning under Incomplete Knowledge. Computational Logic 2000: 807-821

Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, Axel Polleres: Using the dlv System for Planning and Diagnostic Reasoning. WLP 2000: 125-134

Uwe Egly, Michael Fink, Axel Polleres, Hans Tompits: A Web-based Tutoring Tool for Calculating Default Logic Extensions. WebNet 1999: 1251-1252