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location: Answer Set Programming for the Semantic Web

Budva, Montenegro, June 11th 2006. Co-located with the 3d European Semantic Web Conference


Slides, exercises and hands-on will be available soon.


The purpose of this tutorial is to get the audience familiar with the Answer Set Programming (ASP) Paradigm in the perspective of its fruitful usage for Semantic Web applications.

Tutorial Contents and Tentative Schedule

The participants are amply encouraged to bring their own Internet-ready laptops in order to practice with our on-line web interface. Feel free to play with our Online Interface.

What is ASP ?

ASP is a declarative logic programming paradigm with its roots in Knowledge Representation and Logic Programming. Its semantics relies on the notion of Stable Model, which is also the preferred semantics for Disjunctive Logic Programming. Although different, these three notions are sometimes considered as synonims: indeed they have, in a sense, an overlapping meaning. Systems and languages based on ASP are ready for tackling many of the challenges the Semantic Web offers, and in particular, are good candidates for solving a variety of issues which have been delegated to the Rule/Logic Layers in the Semantic Web vision. ASP systems are scalable, allow to mix monotonic with nonmonotonic reasoning, permit to combine rules with ontologies, and can interface external reasoners. Moreover, ASP is especially tailored at solving configuration and matchmaking problems involving reasoning with preferences by featuring easy to use, fully declarative soft & hard constraint specification languages.

Benefits of ASP

ASP and the Semantic Web

Many lines of research currently mix ASP, and other related rule based languages, with Semantic Web technologies. They can be divided in three categories:

Outline of the tutorial content

The tutorial is be divided in units:

Interactive Unit 1. ASP Basics. In this unit the attendees will become familiar with the basic notions and intuitive semantics of ASP. We will lean examples and exercises on common scenarios from the Semantic Web world, using for instance the OWL Wine ontology in order to get users familiar to ASP with known examples. On the one hand this will illustrate the additional and complementary KR capabilities of ASP in these domains, on the other hand this will show how they complement OWL with a fully declarative rule and constraint language. Users will be taught how to use ASP as a declarative KR formalism and query language involving non-determinism, disjunctive rules, strong and default negation and (hard) constraints. Examples will be accessible and executable through an online interface based on a state-of-the-art ASP solver.

Interactive Unit 2. ASP Extensions. In this unit several ASP advanced extensions will be tutored. Particularly, we will present extensions by aggregates known from database query languages; weak constraints, and how these can be used to encode preferences and priorities; rule templates which add a powerful macro-language to ASP; external function calls. Again, attendees will have the opportunity to try out their own examples through an online interface.

Unit 3. Current ASP State-of-the-Art. In this section, we will present an ASP application showcase, demonstrating an information integration scenario solved using the ASP methodology, (see for instance The WASP showcase), as well as pointers to relevant past and current literature and research directions.

Unit 4. Contribution of ASP to the Semantic Web field. In the fourth and fifth unit, we will focus on new extensions of ASP aimed at Semantic Web applications. This first unit in the afternoon unit will survey and present current approaches of mixing ASP with Semantic Web technologies. We will discuss and survey different reductions from Description Logics to ASP and approaches which aim at a semantic integration of rules with the Ontology Layer.

Interactive Unit 5. ASP Semantic Web Extensions Part I. In this unit, we will present those general extensions of ASP which facilitates ASP engines with existing Description logics engines through so-called DL-atoms. We will show how this extension can be used to facilitate a clean interaction of Semantic Web languages with rules still keeping a strict semantic separation of both worlds. Attendees will be able to try out this extension through the provided online interface and experience ASP querying interleaved with reasoning over (DL) ontologies. Applications, advantages and drawbacks compared with the existing proposals from the previous unit will be presented.

Interactive Unit 6. ASP Semantic Web Extensions Part II. In this unit the notion of DL-atom is generalized to the one arbitrary external predicate. Combined with higher order reasoning, this extension can be plugged into existing ASP engines facilitating new fruitful applications, especially in the Semantic Web context. These include integration of ASP with a variety of full first-order reasoners, reification, etc.

Interactive Unit 7. Hands-on Session. Each of the previous units was accompanied with small practical examples. As a final part of the tutorial, the attendees will practice and combine their experiences from the different units with a larger test case. The session will be conducted dividing the audience in small groups which will be guided by one of the presenters through an integrated test scenario where the attendants have to solve certain modelling and problem solving tasks by applying the acquired ASP methodologies.

Intended audience and prerequisites

The tutorial is mainly directed to two categories of attendees:

Although no specific know-how is needed as a prerequisite, basic knowledge about ontologies, web services, rule languages will allow attendees to better understand and follow the tutorial.

The presenters

Some references

(feel free to ask GB Ianni if you wish your ASP/SW related work cited here)

The interactive sessions and the hands-on session will be given by taking advantage of some ASP solvers, in the development of which the presenters are directly involved:

Other known ASP solvers are:

Foundational papers about Answer Set Programming:

Semantic Web & ASP related papers:

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