Catálogo de publicaciones - libros

This chapter covers the mediation aspect in a Semantic Web Services environment. Mediation components should allow any service to speak with any other service in a scalable manner, overcoming the heterogeneity of data formats, terminologies, interaction styles, etc. In this chapter, we decompose mediation in three levels, according to the classification provided in Chap. (1) data mediation, concerned with the transformation of the syntactic format of the messages exchanged by Web Services; (2) ontology mediation, concerned with the transformation of the terminology used inside the messages exchanged and (3) protocol or choreography mediation, concerned with the problem of non-matching message interaction patterns. Business process mediation is not considered, since it requires to perform a task of process re-engineering that is outside the context of research in Semantic Web Services.

This chapter introduces the combination of the formerly described Web Services and Semantic Web technologies to Semantic Web Services. It outlines the vision and goals in the Semantic Web Services area and clarifies terminology in this field. It defines an abstract Semantic Web Service architecture and introduces a life cycle of the relationship between a requester and a provider party. This motivates the subsequent chapters for description, discovery, mediation and invocation of semantically annotated services in the web.

In Artificial Intelligence, knowledge representation studies the formalisation of knowledge and its processing within machines. Techniques of automated reasoning allow a computer system to draw conclusions from knowledge represented in a machine-interpretable form. Recently, ontologies have evolved in computer science as computational artefacts to provide computer systems with a conceptual yet computational model of a particular domain of interest. In this way, computer systems can base decisions on reasoning about domain knowledge, similar to humans. This chapter gives an overview on basic knowledge representation aspects and on ontologies as used within computer systems. After introducing ontologies in terms of their appearance, usage and classification, it addresses concrete ontology languages that are particularly important in the context of the Semantic Web. The most recent and predominant ontology languages and formalisms are presented in relation to each other and a selection of them is discussed in more detail.

In this section we will describe a prototypical application that shows how Semantic Web Services and current state-of-the-art Enterprise Application Integration software can be used to integrate Government services across different service providers. Starting from a use case scenario and the general requirements that build the basis for our prototype, we will describe the generic integration architecture we have developed focusing mainly on the integration aspects of the Semantic Web Services. Following this we will describe the actual prototype application as well as some implementation details. Finally, we will close by a description of the challenges we faced when developing the prototype and by some general conclusions.

Since Web Services are complex artefacts that rely on sophisticated protocols and data formats, it is important to have effective strategies for dealing with this complexity. As a basic concept, the Web Service technologies are structured in a stack model. It is crucial for every Web Service developer to have this model in mind and to have a clear understanding how the single items work together. In this chapter, we will first give an overview of the Web Service technology stack. Then, we will step through this model and discuss the different core technologies in detail. This includes different variants of Web Service transport bindings, SOAP, WSDL and UDDI.