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2 Fundamenta Informaticae

2 2011

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Look-back Techniques for ASP Programs with Aggregates

Faber W., Leone N., Maratea M., Ricca F.

Fundamenta Informaticae

2011

Vol. 107, nr 4

379-413

The introduction of aggregates has been one of the most relevant language extensions to Answer Set Programming (ASP). Aggregates are very expressive, they allow to represent many problems in a more succinct and elegant way compared to aggregate-free programs. A significant amount of research work has been devoted to aggregates in the ASP community in the last years, and relevant research results on ASP with aggregates have been published, on both theoretical and practical sides. The high expressiveness of aggregates (eliminating aggregates often causes a quadratic blow-up in program size) requires suitable evaluation methods and optimization techniques for an efficient implementation. Nevertheless, in spite of the above-mentioned research developments, aggregates are treated in a quite straightforward way in most ASP systems. In this paper, we explore the exploitation of look-back techniques for an efficient implementation of aggregates. We define a reason calculus for backjumping in ASP programs with aggregates. Furthermore, we describe how these reasons can be used in order to guide look-back heuristics for programs with aggregates. We have implemented both the new reason calculus and the proposed heuristics in the DLV system, and have carried out an experimental analysis on publicly available benchmarks which shows significant performance benefits

A Logic-Based System for e-Tourism

Ricca F., Dimasi A., Grasso G., Ielpa S.M., Iiritano S., Manna M., Leone N.

Fundamenta Informaticae

2011

Vol. 105, nr 1/2

35-55

In this paper we present a successful application of logic programming for e-tourism: the iTravel system. The system exploits two technologies that are based on the state-of-the-art computational logic system DLV: (i) a system for ontology representation and reasoning, called OntoDLV; and, (ii) HLX a semantic information-extraction tool. The core of iTravel is an ontology which models the domain of tourism offers. The ontology is automatically populated by extracting the information contained in the tourism leaflets produced byε tour operators. A set of specifically devised logic programs is used to reason on the information contained in the ontology for selecting the holiday packages that best fit the customer needs. An intuitive web-based user interface eases the task of interacting with the system for both the customers and the operators of a travel agency.