Aspect-Oriented Framework for Web Services (AoF4WS): Introduction and Two Example Case Studies

Introduction And Motivations

Web services are an attractive approach for implementing loosely-coupled business processes, which usually spread over companies’ boundaries (Ma, 2005). Over the last few years several efforts have been put into the development of standards related to Web services definition, announcement/discovery, and composition, just to cite a few. The dynamic nature of the business world highlights the continuous pressure on businesses to reduce expenses, increase revenues, generate profits, and remain competitive. This calls for a quick reaction to the market trends, a quick handling of users’ needs, a quick adaptation to unforeseen changes, and last but not least, a quick understanding of forthcoming challenges. To boost the acceptance level of Web services by the IT community as the technology of choice when developing flexible processes, Web services need to adapt to changing nonfunctional requirements with minimal reprogramming and minimal maintenance effort, so that they can be kept independent from the core Web services functionality. Security and self-healing are samples of nonfunctional requirements, and we will be highlighting them in this chapter.

Integrating security and self-healing capabilities into Web services calls for a clear separation between “business” and “management” concerns along which a Web service is defined (Figure 1). For this purpose, we adopt an aspect-oriented programming (AOP) approach to specify and implement this separation (Cottenier & Elrad, 2004; El-Manzalawy, 2005). This approach is part of our long-term research initiative known as aspect-oriented framework for Web services (AoF4WS). This initiative aims at examining the role of aspects in decoupling various concerns in Web services like security and self-healing. The separation between “business” and “management” sides emphasizes the noninvasive requirement that needs to be taken into consideration during the development cycle of a nonfunctional requirement. The mechanisms related, for instance, to security should be confined into one module and thus, should not scatter over the rest of modules of the Web service. Figure 1 illustrates the way concern separation occurs in a fictive Web service referred to as HotelBooking. The business side focuses on details directly related to hotel booking, like checking room availability, rate verification, and confirming client reservation. The management side of a Web service gathers all modules, such as security, self-healing, and monitoring that back the operations of this Web service. Constituents of the management side to be implemented as aspects need to be factored out of the core logic of the Web service.

Figure 1.

Concern separation in a Web service

In the following, we describe the two projects that we have chosen as part of the Ao4FWS initiative. The SC-WS project stands for security concerns of Web services and the SH-WS project stands for self-healing Web services. In Section 2 we present some basic definitions necessary for understanding the chapter. A motivating scenario is also presented in this section. SC-WS and SH-WS projects are described in Section 3 and Section 4, respectively. The chapter concludes in Section 5.