Relazioni Invitate e Tutorial

Relatori Invitati

  • Gerhard Brewka, University of Leipzig, Germania

    Nonmonotonic Tools for Argumentation

    In argumentation, the question whether a (pro)position p is accepted or not is decided by constructing and possibly weighing arguments pro and con p. The arguments are generated from a – possibly inconsistent and/or defeasible – knowledge base. Several nonmonotonic tools have been developed which abstract away from the specific content of the arguments and focus on particular services, for instance for conflict solving among arguments.

    The most popular example of such a tool are Dung’s argumentation frameworks (AFs) which define a "calculus of opposition" and are probably the simplest nonmonotonic systems available. Given a set of arguments with an attack relation among them, AFs come with different semantics, where a semantics specifies which subsets of the arguments are acceptable. The different semantics represent different intuitions how to select arguments, as well as different degrees of skepticism.

    In the talk I will present abstract dialectical frameworks (ADFs), a powerful generalization of AFs where nodes in the argument graph, rather than having an implicit acceptance condition, come with an explicit boolean function specifying when the node is to be accepted based on the status of its parents. This allows us to represent support in addition to attack, and to express flexible ways of taking pro and con arguments into account.

    We illustrate the usefulness of ADFs by reconstructing Carneades argument evaluation structures (CAES). Carneades, developed by Gordon, Prakken and Walton, is an influential and widely cited argumentation system, motivated by the needs of legal argumentation. It covers relevant aspects such as burden of proof, proof standards and the like. We show how CAES can be reconstructed as ADFs. This not only demonstrates the generality of ADFs. It also allows us to lift a restriction of CAES to acyclic sets of arguments and provides the generalized systems with the standard semantics developed by Dung.

  • Gerhard Friedrich, Alpen-Adria University Klagenfurt, Austria

    Why even old AI-folks get very excited about Answer Set Programming

    Twenty years ago, when my project group first tried to use Datalog to solve configuration tasks for a large international company, it failed even for the simplest of cases because of excessive runtime. Other approaches like description logic were not even able to express the problem.

    However, times have changed dramatically and the success of Answer Set Programming (ASP) has been underlined by many prominent success stories. So the question is not if ASP will be successful in solving practical problems but rather whether it can become the major knowledge representation language.

    In order to answer this question I will investigate three classical problem domains of Artificial Intelligence: (1) diagnosis-from-first principles and repair which has recently been applied to self-healing processes and web services, (2) configuration, and (3) recommender systems.

    I will show that ASP allows these problems to be represented very simply and that ASP provides reasoning services which closely fit the original problem specifications. However, there is still work for the ASP community. Based on long-standing experience in developing real-world knowledge-based systems I will pinpoint open issues which deserve further investigation in order to expand the applicability of ASP.

    Concluding, ASP reasoning systems provide the knowledge representation and processing environments that many AI-folks have waited a long time for.


  • Axel Polleres, National University of Ireland, Irlanda

    The Role of Logics and Logic Programming in Semantic Web Standards (OWL2, RIF, SPARQL1.1)

    In this tutorial, we will give an overview of the new W3C standards OWL2 and RIF and their interplay with the query language SPARQL, particularly the new version of SPARQL, SPARQL 1.1 currently being worked on in W3C.

    As we will see, fragments of these standards can be reduced to fragments of Logic Programming, and practical systems consuming these Web languages can be developed on top of engines such as DLV.