Service-Oriented Computing: From Web Services to Service-Oriented Components

Introduction

The Service-Oriented Computing (SOC) represents today a solution of choice to deal with integration issues. SOC promotes the use of well-defined composition units – services – to support the rapid development of applications. The central objective of this approach is to reduce dependencies among composition units, where a unit is typically some remote functionality accessed by clients. By reducing such dependencies, each element can evolve separately, so the application is more flexible than monolithic applications (Papazoglou & Georgakopoulos, 2003), (Escoffier, 2007). Services are assembled in a Service-Oriented Architecture (SOA) that provides mechanisms and rules to specify, publish, discover and compose available services. Depending on the target application domain, different protocols and mechanisms are used to implement SOA. For instance, Web Services (www.w3c.org) are dominant to integrate IT applications. UPnP (UPnP Forum, 2008) or DPWS (Microsoft, 2006) are preferred in small area networks for devices. OSGi (OSGi Alliance, 2007) and iPOJO (Escoffier & Hall, 2007) are often used in centralized, embedded equipments.

The service-oriented approach has been implemented in many domains. Figure 1 illustrates the use of service technologies in different application domains.

Figure 1.

Service technologies and application domains

This chapter is organized as follows. First, we present the Web Services technology and the requirements of application integration which are solved by Web Services. The second section deals with the pervasive computing and the technologies adapted to this domain: UPnP and DPWS. The third section introduces the Service-Oriented Computing in dynamic environment and the technologies implementing this new paradigm: OSGi and iPOJO. Before the conclusion, the fourth section proposes a comparison of the service technologies presented in the previous sections.

Application Integration

Web Services are the most popular and well-known technology for implementing Service-Oriented Architecture, both in the industry and the academia. In this section, we will present the main Web Services principles. Then, we will describe the three standards this technology uses: WSDL, UDDI and SOAP.