Abstract. It is recognised that institutions are potentially powerful means for making agent interactions effective and efficient, but institutions will only really be useful when, as in other safety-critical scenarios, it is possible to prove that particular properties do or do not hold for all possible encounters. In contrast to symbolic model-checking, answer set programming permits the statement of problems and queries in domain-specific terms as executable logic programs, thus eliminating the gap between specification and verification language. Furthermore, results are presented in the same terms. In this paper we describe the use of answer set programs as an institutional modelling technique. We demonstrate that our institutional model can be intuitively be mapped into an answer set program such that the ordered event traces of the former can be obtained as the answer sets of the latter, allowing for an easy way to query properties of models. 1

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. ASP is a declarative programming paradigm with its roots in Knowledge Representation and Logic Programming. 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. We introduce the attendees to the ASP basics and its principal extensions tailored at Semantic Web applications. We discuss the current impact of Answer Set Programming in the Semantic Web Area and possible future directions. Applications and exercises are presented. The attendees will practice through an online interface using one of the state-of-the-art ASP solvers and some of its extensions.

Abstract. The PLATYPUS approach offers a generic platform for distributed answer set solving, accommodating a variety of different architectures for distributing the search for answer sets across different processes and different search modes for modifying search behaviour. We describe two major extensions of PLATYPUS. First, we present its probing mode which provides a controlled non-linear traversal of the search space. Second, we present its new multithreading architecture allowing for intra-process distribution. Both contributions are underpinned by experimental results illustrating their computational impact. 1

Abstract. We propose an approach to distributed Answer Set Solving based on Message Passing. Our approach aims at taking advantage of modern ASP solvers rather than proposing a genuine yet involved parallel ASP solver. To this end, we rely upon a simple master-worker architecture in which each worker amounts to an off-the-shelf ASP solver augmented with a separate communication module being only lightly connected to the actual solver. The overall communication is driven by the workers ’ communication modules, which asynchronously exchange messages with the master. We have implemented our approach and report upon an empirical study demonstrating its computational impact. 1

Abstract. We present an approximation theory for the extended answer set semantics, using the concept of an approximation constraint. Intuitively, an approximation constraint, while satisfied by a “perfect” solution, may be left unsatisfied in an approximate extended answer set. Approximations improve as the number of unsatisfied constraints decreases. We show how the framework can also capture the classical answer set semantics, thus providing an approximative version of the latter. 1

Abstract. This paper describes the problems with debugging tools for answer set programming, a declarative programming paradigm. Current approaches are difficult to use on most applications due to the considerable bottlenecks in communicating the reasons to the user. In this paper we examine the reasons for this and suggest some possible future directions. 1

Abstract. In the last few years, the microprocessors technologies have been definitely moving to multi-core architectures, in order to improve performances as well as reduce power consumption. This makes the real Symmetric MultiProcessing (SMP) finally available even on non-dedicated machines, and paves the way to the development of more scalable softwares. Notably, the recent application of Answer Set Programming (ASP) in different emerging areas, such as knowledge management or information extraction/integration, has been showing that scalability is a crucial issue also for ASP systems. Among the tasks performed by ASP systems, the instantiation process, which consists of generating a variable-free program equivalent to the input one, is one of the most expensive from a computational viewpoint, especially for real-world problems where the input data may be huge. In this paper we experiment with a brand new strategy, that we implemented into the ASP system DLV, exploiting parallelism for the instantiation of ASP programs. The results confirm that the proposed technique significantly improves the performances of the system, particularly for solving real-world problems. 1