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This chapter is meant as a motivation of why and how Web Services have evolved. Starting from the increasing need for integration of IT solutions, we argue that Web Services have something to offer, especially for the important fields of Business-to-Business (B2B) and Enterprise Application Integration (EAI). However, this is only the beginning of a new road, leading to the radically new software technology of Service-Oriented Architectures (SOA).

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.

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.

The development of ontologies is comparable in complexity with the development of a complex software. Therefore, it is not enough just to be familiar with the available ontology formalisms to build high-quality ontologies. Development methodologies are needed, which structure the steps of the ontology development process. This chapter will introduce two popular methodologies – On-To-Knowledge and METHONTOLOGY – which show most of the major ideas behind ontology methodologies. Creating the conceptual ontology model – which is one of the steps in the ontology development process – is a highly complex task, and methodologies alone do not provide solutions how to perform it. This chapter therefore also provides an overview of best-practice ontology design principles, which provide standard solutions for the most common problems. A discussion about the modularisation of big ontologies closes this chapter.

In this chapter, we give a brief introduction into the main idea of the Semantic Web, namely making better use and enabling more intelligent applications for Web-accessible information by accompanying them with machine-understandable, semantic meta data; we sketch the major methodological framework behind, consisting of two intertwined, orthogonal processes, the knowledge process and the knowledge meta process–the latter is concerned with ontology engineering, the former uses ontologies for ontology-based meta-data assignment to Web resources, i.e. for semantic annotation. The major part of the chapter is devoted to the idea of semantic annotation, requirements and functionalities of annotation tools, an example implementation and an overview of the state of research and practice in semantic annotation.

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.

Web Services have added a new level of functionality to the current Web, making the first step to achieve seamless integration of distributed components. Nevertheless, current Web Service technologies only address the syntactical aspects of a Web Service and, therefore, only provide a set of rigid services that cannot adapt to a changing environment without human intervention. The human programmer has to be kept in the loop and scalability as well as economy of Web Services are limited. The description of Web Services in a machine-understandable fashion is expected to have a great impact in areas of e-Commerce and Enterprise Application Integration, as it can enable dynamic and scalable cooperation between different systems and organisations. These great potential benefits have led to the establishment of an important research activity, both in industry and in academia, which aims at realising Semantic Web Services. This chapter outlines aspects of the description of semantic Web Services.

Web Services expose machine-processable interfaces that provide flexible access to their functionality in network environments for realising application integration scenarios. As any other web resource, it is desirable to locate and get access to Web Services by specifying relevant properties in the form of a request, similar to how websites are located via search engines. When annotated with semantic information about their functionality, Web Services can be located based on their actual capabilities rather than on their interfaces only. Discovery is the task of locating Web Services by means of their semantic annotations. This typically involves matching of semantic capability descriptions for requested service against those for advertised services. This chapter discusses the notion of discovery of services in the Semantic Web. It gives an overview on approaches to realise discovery by different matching techniques and elaborates on matching of service annotations within the description logic formalism. This particular approach is illustrated by an example taken from the logistics domain.

This chapter deals about Semantically annotated Web Service (SWS) composition, one of the main challenges for the Semantic Web. We define the principles of SWS composition as well as the difficulties it raises. We follow with an overview of the different approaches envisioned in the research community. We also present an efficient solving method for this problem based on configuration. This technic uses a constrained object model as knowledge representation, which we precisely define in this chapter.