Section 4.23. What is the basic structure of an enterprise service?

4.23. What is the basic structure of an enterprise service?

An enterprise service is composed of two things: the service interface and the service implementation . The interface is a structure defined by a WSDL file and code that sends and receives messages to and from applications and other services that wish to consume the service, and the implementation contains the functionality and performs the actual work.

The interface itself is composed of service operations, or the specific ways a service is invoked. Each service operation has an interface and implementation that understand information received by the service, perform any transformation that takes place, manage any persistent state that is changed, and prepare any information sent back to the caller. Also present is a piece of metadatathe service documentationthat explains the functionality and other inner workings of the service implementation.

It's important to understand that each piece of functionality contained within the service requires a service operation to expose that piece for consumption by a service call from an application. For extremely simple services, only one service operation may be present. But most have at least several operations. Enterprise services are always a gateway to functionality that is provided by an existing system called a service provider, which may exist in the form of an exposed enterprise application or which might be built from scratch. Figure 4-10 shows the relationship between service operations, services, and service providers.

Figure 4-10. Services and service operations

It's important to understand here that not all enterprise applications are able to expose the same amount of functionality with the same level of ease via service operations. Enterprise services resting atop business objectsan organized container of functionality and data designed specifically to operate well within an ESA frameworkare able to offer a greater variety of service operations more easily than a service consuming functionality from an enterprise application that was never designed to provide discrete services.