ALPSWS on Wednesday, August 16th

Session 1: LP and the Semantic Web (09:00‑10:30)

09:00‑09:30	Thomas Eiter (TU Vienna) Giovambattista Ianni (Vienna University of Technology) Roman Schindlauer (Vienna University of Technology) Hans Tompits (Vienna University of Technology) Kewen Wang (Griffith University, Australia) Forgetting in Managing Rules and Ontologies The language of HEX-programs under answer set semantics is designed for interoperating with heterogeneous sources via external atoms and for meta-reasoning via higher-order literals in the context of the Semantic Web. As an important technique in managing knowledge bases, the notion of forgetting has received increasing interest in knowledge representation. This paper introduces a semantics-based theory of forgetting for HEX-programs and a class of OWL ontologies, which allows to fully employ semantic information in managing ontologies like editing, merging, aligning, or redundancy removal.
09:30‑10:00	Edna Ruckhaus (Universidad Simon Bolivar, Dept. Computer Science) Maria-Esther Vidal (Universidad Simon Bolivar, Dept. Computer Science) Eduardo Ruiz (Universidad Simon Bolivar) Query Evaluation and Optimization in the Semantic Web In this paper we address the problem of answering Web on- tology queries efficiently. We formalize an ontology as a Deductive On- tology Base (DOB), a deductive database that comprises the ontology’s inference axioms and facts, and we present a cost-based query optimiza- tion technique for DOB. A hybrid cost model is proposed to estimate the cost and cardinality of basic and inferred facts. Cardinality and cost of inferred facts are estimated using an adaptive sampling technique, while techniques of traditional relational cost models are used for esti- mating the cost of basic facts and conjunctive ontology queries. Finally, we implement a dynamic-programming optimization algorithm to iden- tify query evaluation plans that minimize the number of intermediate inferred facts. We modeled a subset of the Web ontology language OWL Lite as a DOB, and performed an experimental study to analyze the predictive capacity of our cost model and the benefits of the query optimization technique. Our study has been conducted over synthetic and real-world OWL ontologies, and shows that the techniques are accurate and improve query performance.
10:00‑10:30	Thomas Eiter (TU Vienna) Giovambattista Ianni (Vienna University of Technology) Roman Schindlauer (Vienna University of Technology) Hans Tompits (Vienna University of Technology) dlvhex: A Tool for Semantic-Web Reasoning under the Answer-Set Semantics We briefly report on the development status of dlvhex, a reasoning engine for hex-programs, which are nonmonotonic logic programs with higher-order atoms and external atoms. Higher-order features are widely acknowledged as useful for various tasks and are essential in the context of meta-reasoning. Furthermore, the possibility to exchange knowledge with external sources in a fully declarative framework such as answer-set programming (ASP) is particularly important in view of applications in the Semantic-Web area. Through external atoms, hex-programs can deal with external knowledge and reasoners of various nature, such as RDF datasets or description logics bases.

Break (10:30‑11:00)

Session 2: LP and Semantic Web Services (11:00‑12:30)

11:00‑11:30	Stijn Heymans (DERI Innsbruck, University of Innsbruck) Livia Predoiu (DERI Innsbruck, University of Innsbruck) Cristina Feier (DERI Innsbruck, University of Innsbruck) Jos de Bruijn (DERI Innsbruck, University of Innsbruck) Davy Van Nieuwenborgh (Vrije Universiteit Brussel) G-Hybrid Knowledge Bases Recently, there has been a lot of interest in the integration of Description Logics and rules on the Semantic Web. We define g-hybrid knowledge bases as knowledge bases that consist of a Description Logic knowledge base and a guarded logic program, similarly to the DL+log knowledge bases from [22]. G-hybrid knowledge bases enable an integration of Description Logics and Logic Programming where, unlike other approaches, variables in the rules of a guarded program do not need to appear in positive non-DL atoms of the body: DL atoms can act as guards as well. Decidability of satisfiability checking of g-hybrid knowledge bases is shown for the particular DL DLRO −{≤} , which is close to, and in some respects more expressive than, OWL DL, by a reduc- tion to guarded programs under an open answer set semantics. Moreover, we show 2-EXPTIME-completeness for satisfiability checking of those DLRO −{≤} g-hybrid knowledge bases. Finally, we discuss advantages and disadvantages of our approach compared with DL+log knowledge bases.
11:30‑12:00	Viviana Mascardi (DISI, University of Genova, Italy) Giovanni Casella (1: DISI, University of Genova, Italy; 2: DMI, University of Salerno, Italy) Intelligent Agents that Reason about Web Services: a Logic Programming Approach The paper proposes to factor three leading edge technologies, namely Web Services, Intelligent Agents, and Computational Logic, for implementing logic-based agents that reason about interaction protocols specified using standard languages for Web Services. A working multiagent system prototype, where agents implemented in Prolog reason about protocols expressed in WS-BPEL, has been developed.
12:00‑12:30	Srividya Kona (University of Texas at Dallas) Ajay Bansal (University of Texas at Dallas) Gopal Gupta (University of Texas at Dallas) Thomas Hite (Metallect Corp.) Efficient Web Service Discovery and Composition using Constraint Logic Programming Service-oriented computing is gaining wider acceptance. For Web services to become practical, an infrastructure needs to be supported that allows users and applications to discover, deploy, compose and synthesize services automatically. This automation can take place effectively only if formal semantic descriptions of Web services are available. In this paper we present an approach for automatic service discovery and composition with both syntactic and semantic description of Web services. In syntactic case, we use a repository of services described using WSDL (Web Service Description Language). In the semantic case, the services are described using USDL (Universal Service-Semantics Description Language), a language we have developed for formally describing the semantics of Web services. In this paper we show how the challenging task of building service discovery and composition engines can be easily implemented and efficiently solved via (Constraint) Logic programming techniques. We evaluate the algorithms on repositories of different sizes and show the results.

Lunch break (12:30‑14:00)

Session 3: Policies and Posters (14:00‑15:30)

14:00‑14:30	Marco Alberti (ENDIF, University of Ferrara) Federico Chesani (DEIS, University of Bologna) Marco Gavanelli (ENDIF, University of Ferrara) Evelina Lamma (ENDIF, University of Ferrara) Paola Mello (DEIS, University of Bologna) Marco Montali (DEIS, University of Bologna) Paolo Torroni (DEIS, University of Bologna) Policy-based reasoning for smart web service interaction We present a vision of smart, goal-oriented web services that reason about other services' policies and evaluate the possibility of future interactions. To achieve our vision, we propose a proof theoretic approach. We assume web services whose interface behaviour is specified in terms of reactive rules. Such rules can be made public, in order for other web services to answer the following question: ``is it possible to inter-operate with a given web service and achieve a given goal?'' In this article we focus on the underlying reasoning process, and we propose a declarative and operational abductive logic programming-based framework, called WAVe.
14:30‑15:00	Posters and Demos
15:00‑15:30	Open space: Introduction and Topic finding

Break (15:30‑16:00)

Session 4: Open-Space (16:00‑18:30)

16:00‑17:00	Open-Space, part I
17:00‑18:00	Open-Space, part II
18:00‑18:30	Open-Space, Report back