USDL: A Service-Semantics Description Language for Automatic Service Discovery and Composition1

Introduction

A Web service is a program available on a web-site that “effects some action or change” in the world (i.e., causes a side-effect). Examples of such side effects include a web-base being updated because of a plane reservation made over the Internet, a device being controlled, and so forth. The next milestone in the Web’s evolution is making services ubiquitously available. As automation increases, these Web services will be accessed directly by the applications themselves rather than by humans. In this context, a Web service can be regarded as a “programmatic interface” that makes application to application communication possible. An infrastructure that allows users to discover, deploy, synthesize and compose services automatically needs to be supported in order to make Web services more practical.

To make services ubiquitously available we need a semantics-based approach such that applications can reason about a service’s capability to a level of detail that permits their discovery, deployment, composition and synthesis. Several efforts are underway to build such an infrastructure. These efforts include approaches based on the semantic web (such as OWL-S (OWL-S, 2003)) as well as those based on XML, such as Web Services Description Language (WSDL (WSDL, 2001)). Approaches such as WSDL are purely syntactic in nature, that is, they merely specify the format of the service. In this article we present an approach that is based on semantics. Our approach can be regarded as providing semantics to WSDL statements. We present the design of a language called Universal Service-Semantics Description Language (USDL) which service developers can use to specify formal semantics of Web services (Bansal et al., 2005; Simon, Bansal, Mallya, Kona, Gupta, & Hite, 2005). Thus, if WSDL can be regarded as a language for formally specifying the syntax of Web services, USDL can be regarded as a language for formally specifying their semantics. USDL can be thought of as formal service documentation that will allow sophisticated conceptual modeling and searching of available Web services, automated composition, and other forms of automated service integration. For example, the WSDL syntax and USDL semantics of Web services can be published in a directory which applications can access to automatically discover services. That is, given a formal description of the context in which a service is needed, the service(s) that will precisely fulfill that need can be determined. The directory can then be searched for the exact service, or two or more services that can be composed to synthesize the required service.