Answer Set Programming for the Semantic Web

supported by the Austrian Science Funds (FWF) under project number P17212 and and the European Commission through the IST REWERSE Network of Excellence.


Project team

Motivation and Background

The World Wide Web (WWW) is currently by far the largest and most frequently-accessed data repository available. However, most of the documents on the Web are only suitable for direct use by human consumers, but are not accessible for automated information processing. Indeed, the HTML standard enables only the description of the layout of a document, but not of its content. Hence, a large body of processes cannot be fully automated and there is no common way of expressing and manipulating information and knowledge about Web data.

This shortcoming is clearly recognized by the scientific community and there is currently extensive work under way to build the foundations of the next-generation Web addressing these issues.

As the global normative institution, the World Wide Web Consortium (W3C) recently launched the Semantic Web Activity in order to define a suitable infrastructure which should allow Web-content to be machine accessible. The Semantic Web can be divided into the following layers:

  • At the bottom layer, there are standards for identifying resources (URI: universal record identifier) and for representing typed text (Unicode);
  • the next layer contains languages for annotating information items, like XML (including namespaces and XML Schema);
  • the third layer provides formalisms to express meta-data expressions by means of the Resource Description Framework (RDF) and its extension RDF Schema;
  • the fourth layer contains ontology vocabularies to express relative semantics to concepts (like "flying is a form of traveling"); and
  • the final layers deal with logic and trust issues.
While the bottom and XML layer are so far fully functional, and the RDF language (and RDF Schema) is well-defined and standardized, the currently emerging layer of the Semantic Web is the ontology layer. Here, the Ontology Web Language (OWL) is proposed as standard by the W3C. However, still an open issue is the specification of the final layers of the Semantic Web.

Reasoning support for the Semantic Web is currently mainly restricted to terminological reasoning in description logics and there is no broad consensus on what will constitute the logical layer of the Semantic Web. Many open questions have not been tackled yet, ranging from representational and syntactic matters to the question which out of the numerous different reasoning and proof mechanisms should be employed.

What is missing for fruitful advances towards some of the open problems are methods, languages, and implemented systems for the Semantic Web that

  • support nonmonotonic formalisms and the representation of default knowledge, i.e., the mechanism of "jumping to conclusions" in the presence of incomplete or uncertain information; in particular, provide the coupling of nonmonotonic formalisms and description logics underlying ontology languages, both concerning theory and implementation;
  • handle preferences and constraints; and
  • implement a fully declarative semantics

Goal of the project

The goal of this project is to research methods for providing advanced reasoning services in the context of the Semantic Web, using declarative knowledge representation and reasoning techniques. In particular, we shall investigate the use of logic programming under the answer set semantics for realizing languages and tools which extend the capabilities of current approaches, in order to support reasoning aware querying of the Web. Special attention will be given to the study of suitable models and algorithms for dealing with incomplete and preference information. Furthermore, we will develop modules to support advanced reasoning tasks for particular applications in the context of policy specification and personalized information systems.

State of the Project and Outlook

We started our project by examining possibilities of defining an interface between logic programs and description logic knowledgebases. Our approach introduces so-called description logic programs (or dl-programs), which are of the form KB=(L,P), where L is a knowledge base in a description logic, and P is a finite set of description logic rules (or dl-rules). Such dl-rules are similar to usual rules in logic programs with negation as failure, but may also contain queries to L in their bodies which are given by special atoms (on which possibly default negation may apply). The queries described by these dl-atoms can be
  • concept inclusion axioms,
  • concept membership axioms, and
  • role membership axioms.
Besides the flow of information from L to P, another important feature of dl-rules is that queries to L also allow for specifying an input from P. This is achieved by dynamic update operators through which the extensional part of L can be modified by the facts of a predicate of P before the query is carried out. As of August 2004, a prototype implementation is available on the Web. We implemented both the Well-founded and the Answer Set Semantics for dl-programs, with an Ontology given in OWL DL. This prototype employs DLV for LP reaoning and RACER for querying OWL knowledge bases.


Thomas Eiter, Giovambattista Ianni, Roman Schindlauer, and Hans Tompits. DLV-HEX: Dealing with Semantic Web under Answer-Set Programming. In 4th International Semantic Web Conference (ISWC 2005), 2005. System poster.

Thomas Eiter, Giovambattista Ianni, Roman Schindlauer, and Hans Tompits. Effective Integration of Declarative Rules with External Evaluations for Semantic Web Reasoning. Submitted for publication, December 2005.

Thomas Eiter, Giovambattista Ianni, Roman Schindlauer, and Hans Tompits. NLP-DL: A KR System for Coupling Nonmonotonic Logic Programs with Description Logics. In 4th International Semantic Web Conference (ISWC 2005), 2005. System poster.

Thomas Eiter, Giovambattista Ianni, Roman Schindlauer, and Hans Tompits. Nonmonotonic Description Logic Programs: Implementation and Experiments. In F. Baader and A. Voronkov, editors, Proceedings 12th International Conference on Logic for Programming, Artificial Intelligence and Reasoning (LPAR 2004), number 3452 in LNCS, pages 511-517. Springer, 2005.

Thomas Eiter, Giovambattista Ianni, Roman Schindlauer, and Hans Tompits. A Uniform Integration of Higher-Order Reasoning and External Evaluations in Answer Set Programming. In L. P. Kaelbling and A. Saffiotti, editors, Proceedings of the 19th International Joint Conference on Artificial Intelligence (IJCAI-05), pages 90-96. Professional Book Center, Denver, USA, 2005.

Roman Schindlauer. Nonmonotonic Logic Programs for the Semantic Web. In M. Gabbrielli and G. Gupta, editors, Proceedings of the 21st International Conference on Logic Programming (ICLP 2005), number 3668 in LNCS, pages 446-447. Springer, 2005.

Grigoris Antoniou, Matteo Baldoni, Cristina Baroglio, Robert Baumgartner, Fran c cois Bry, Thomas Eiter, Nicola Henze, Marcus Herzog, Wolfgang May, Viviana Patti, Sebastian Schaffert, Roman Schindlauer, and Hans Tompits. Reasoning Methods for Personalization on the Semantic Web. Annals of Mathematics, Computing and Teleinformatics, 2(1):1-24, 2004. ISSN 1109-9305. Invited paper.

Thomas Eiter, Thomas Lukasiewicz, Roman Schindlauer, and Hans Tompits. Combining Answer Set Programming with Description Logics for the Semantic Web. In Didier Dubois, Christopher Welty, and Mary-Anne Williams, editors, Proceedings Ninth International Conference on Principles of Knowledge Representation and Reasoning (KR 2004), June 2-5, Whistler, British Columbia, Canada, pages 141-151. Morgan Kaufmann, 2004.

Thomas Eiter, Thomas Lukasiewicz, Roman Schindlauer, and Hans Tompits. Well-founded Semantics for Description Logic Programs in the Semantic Web. In G. Antoniou and H. Boley, editors, Proceedings RuleML 2004 Workshop, ISWC Conference, Hiroshima, Japan, November 2004, number 3323 in LNCS, pages 81-97. Springer, 2004.

Thomas Eiter, Michael Fink, Roman Schindlauer, and Hans Tompits. Answer Set Programming for Intelligent Web Services. ÖGAI Journal (J. of the Austrian Society for AI), 22(2):17-22, 2003. Project-Report.

Thomas Eiter, Thomas Lukasiewicz, Roman Schindlauer, and Hans Tompits. Combining Answer Set Programming with Description Logics for the Semantic Web. TechnicalReport INFSYS RR-1843-03-13, Institut für Informationssysteme, Technische Universität Wien, A-1040 Vienna, Austria, December 2003. Preliminary report.

Related courses at our department

(Information for students - only in German.)

Note that these tasks correspond to the current state and demands of the project and can slightly be altered accordingly.

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