Sommerville-Software-Engineering-10ed

18.3 ■ Service engineering 533
Service
candidate
identification
Service design
Service
implementation
and deployment
Figure 18.8 The service
engineering process
Service
requirements
Service interface
specification
Validated and
deployed service
18.3 Service engineering
Service engineering is the process of developing services for reuse in service-oriented
applications. It has much in common with component engineering. Service engineers
have to ensure that the service represents a reusable abstraction that could
be useful in different systems. They must design and develop generally useful
functionality associated with that abstraction and ensure that the service is robust
and reliable. They have to document the service so that it can be discovered and
understood by potential users.
As shown in Figure 18.8, there are three logical stages in the service engineering
process:
1. Service candidate identification, where you identify possible services that might
be implemented and define the service requirements.
2. Service design, where you design the logical service interface and its implementation
interfaces (SOAP-based and/or RESTful).
3. Service implementation and deployment, where you implement and test the service
and make it available for use.
As I discussed in Chapter 16, the development of a reusable component may
start with an existing component that has already been implemented and used in
an application. The same is true for services—the starting point for this process
will often be an existing service or a component that is to be converted to a service.
In this situation, the design process involves generalizing the existing component
so that application-specific features are removed. Implementation means
adapting the component by adding service interfaces and implementing the
required generalizations.
18.3.1 Service candidate identification
The basic idea of service-oriented computing is that services should support business
processes. As every organization has a wide range of processes, many possible
services may be implemented. Service candidate identification therefore involves