Denotation of Semantic Web Services Operations through OWL-S Marco Luca Sbodio Italy Innovation Center Hewlett Packard Italiana C.so Trapani 16, 10139 Torino, Italy marco.sbodio@hp.com Claude Moulin University of Compi` egne, CNRS, Heudiasyc Centre de Recherches de Royallieu 60205 Compi` egne, France claude.moulin@utc.fr Abstract Emerging semantic web service description for- malisms, such as OWL-S, allow for a definition of the semantic of services. Describing input and output types is not sufficient to declaratively and unambiguously de- note the operations offered by a web service. Two ser- vices may have the same input and output types and have completely different semantics of their operation. In this paper we present an approach for the spec- ification of a web service denotation based on OWL-S capabilities, and an algorithm for dynamic discovery of services exploiting their denotation. We show how preconditions and results of the OWL-S formalism can be used to constrain the actual denotation of a service, and we describe how an agent can perform dynamic dis- covery of services exploiting their denotation. In our scenario, an agent has to search for the appropriate service, and verify that this service is able to produce the information that the agent needs. 1. Introduction Web services constitute the building blocks of ser- vice oriented architectures. They offer modularity, flex- ibility and interoperability. Web services standards en- sure the definitions of platform and language indepen- dent functional interfaces, and enforce the decoupling between interfaces and implementation. Although the WSDL description of a web service is a precise defini- tion of its functional interface, it does not declaratively and unambiguously denote the semantics of the oper- ations offered by the web service. The semantic web services vision [1] is pursued by several emerging formalisms and frameworks, such as WSMO [20], SWSF [21] and OWL-S [15]. The Web Service Modeling Ontology (WSMO) defines an ex- plicit conceptual model for Semantic Web Services [18]. It provides a framework for the description of Semantic Web Services that enables seamless business integra- tion through formal descriptions [16, 17]. Although the aims of both WSMO and OWL-S are the same, they present some differences in their approach; a detailed comparison between OWL-S and WSMO is presented in [19]. Our work is based on OWL-S, and it explores how the denotation of a web service can be unambiguously specified using OWL-S Process ontology, through the definition of input and output types, and the declara- tion of preconditions and results. The paper is structured as follows. In Section 2 we give an overview of the approach. In Section 3 we in- troduce a simple reference scenario, which will be used throughout the paper to illustrate our approach. Sec- tion 4 gives an overview of the OWL-S features that allow for a complete denotation of a service; in Section 5 we show how OWL-S features are used to describe the services in our reference scenario, and we explain how we use them to achieve a full denotation of the services. In Section 6 we present an algorithm that shows how an agent can perform dynamic discovery of services exploiting their denotation. We conclude with a comparison on related works in Section 7. 2. Overview We aim at automating the dynamic discovery of web services performed by an agent seeking to satisfy some goal. In the discovery process it is necessary to use the full semantic denotation of the web service operations (input/output types, preconditions and results) in or- der to assess if a service is appropriate to fulfill the agent’s goal. Specifically, we use preconditions and re- sults to declare constraints among inputs and output of a web service in order to disambiguate its operations. Given a set of web services, we assume that their OWL-S descriptions are available through a semantic