Web Service Composition using Answer Set Programming

The description of interactions among Web Services with regard to the exchange of messages, their composition, and the sequences in which they are transmitted and received is an important problem. While some efforts tackle this problem by defining standards for static processes others aim at composing complex services on-the-fly using AItechniques. The present paper follows this AI approach and suggests a solution that uses Answer Set Programming (ASP) as a mean to achieve the composition goal. In particular, it shows how Web service descriptions and customer requests are mapped to the input language of the ASP software DLV [1]. Furthermore, it shows how composition goals and constraints can be defined to guide the composition challenge. Finally, it presents a tool that serves as a framework to build complex services and that uses DLV as one of its back-end solvers. The approach was evaluated in the first Web service composition contest and has won the first prize. 1 Web Service Composition In recent research related to Web services, several initiatives are aiming to provide means to allow easy integration of heterogeneous systems by defining languages, methods, or platforms. Some of these efforts (e.g. BPEL [2], OWL-S [3]) aim towards static processes with a priori knowledge of all possible execution paths, or by applying AI methods to compose complex services on-the-fly for an individual service requester. A Web service is a collection of protocols and standards used for exchanging data between applications. Software applications written in various programming languages and running on various platforms can use web services to exchange data over computer networks like the Internet in a manner similar to interprocess communication on a single computer. 1 DLV is an international cooperation between the University of Calabria and the Vienna University of Technology. More information about DLV available at http://www.dbai.tuwien.ac.at/proj/dlv/ 2 The first Web Service Composition Contest took place in Hongkong in March, 2005, http://www.comp.hkbu.edu.hk/ ̃eee05/contest/