Service Composition with Directories Ion Constantinescu, Walter Binder, and Boi Faltings Ecole Polytechnique F´ ed´ erale de Lausanne (EPFL) Artificial Intelligence Laboratory CH-1015 Lausanne, Switzerland firstname.lastname@epfl.ch Abstract. This paper presents planning-based service composition algorithms that dynamically interact with a potentially large-scale directory of service advertisements in order to retrieve matching service advertisements on demand. We start with a simple algorithm for untyped services, similar to a STRIPS planner. This algorithm is refined in two steps, first to exploit type information, and second to support partial type matches. An evaluation confirms that the algorithms scale well with increasing size of the directory and that the support for partial type matches is essential to achieve a low failure rate. 1 Keywords: Service composition, planning, service discovery, semantic web services. 1 Introduction Today the predominant way we interact with the Web is via browsers that manipulate information by rendering it in a human-readable way. However, there is an evolution towards the automatisation of many processes on the Web, which may result in computer-to-computer interactions becoming predominant over current human-to- computer interactions. For modeling computer-to-computer interactions, currently the de-facto paradigm is that of “services”. But making services automatically interact with each other raises a number of difficult problems, currently under hard scrutiny by in- dustrial and academic research. The Semantic Web [14] is fundamental for such computer-to-computer interactions to become reality, since it provides an universally accessible platform and computer- understandable semantics for data to be shared and processed by automated tools. Ex- perts have already developed a range of mark-up frameworks and languages, notably the revised Resource Description Framework (RDF) [29] and the Web Ontology Lan- guage (OWL) [28], which mark the emergence of the Semantic Web as a broad-based, commercial-grade platform. Service discovery is the process of locating providers advertising services that can satisfy a service request specified by a service consumer. Automated service composi- tion addresses the problem of assembling services based on their functional specifica- tions in order to achieve a given task and to provide extra functionality. When discovery 1 The work presented in this paper was partly carried out in the framework of the EPFL Center for Global Computing and supported by the Swiss National Funding Agency OFES as part of the European projects KnowledgeWeb (FP6-507482) and DIP (FP6-507483). W. L ¨ owe and M. S ¨ udholt (Eds.): SC 2006, LNCS 4089, pp. 163–177, 2006. c  Springer-Verlag Berlin Heidelberg 2006