Functional Description of Services

Where the previous chapter defined the semantics of WSML ontologies (the static knowledge component of Web service descriptions), this chapter describes how WSML can be used to capture the functionality of Web services. We consider both set-based and state-based capabilities, describing the models underlying these kinds of description, as well as the formal relations that can be defined between goals and Web services based on these models.

In general it is important to understand the conceptual model and the particular assumptions underlying each specific approach to service description. Different approaches vary greatly in the level of detail that can be expressed. In terms of functional descriptions we are interested in modelling what a service does as opposed to how a certain functionality is achieved. If we consider for example a Web service capable of processing credit card payments, we are interested in the details of this functionality, i.e., which credit cards are accepted (Visa, Master Card, JCB, …), which currencies and what kind of fraud checking is provided. In this chapter we are not concerned with non-functional aspects such as the supported transport layer security or the guarantees in terms of service availability.

In the remainder of the chapter we will first give an overview of the most prominent approaches to the functional description ofWeb services, in Section 6.1. We then proceed with a description of the models underlying capability descriptions, as well as notions of consistency and capability matching, both for set-based and state-based capability descriptions, in the Sections 6.2 and 6.3, respectively.