While it is clear from the term that enterprise services are the central element of ESA, it is far from clear what that means in detail. One measure of expertise in ESA is the length of the answer someone can give to the question, what is an enterprise service? The more dimensions that someone can discuss with some degree of substance, the more likely that person will be able to quickly make sense of ESA and put it to work in an organization. This section will take you on a tour of all of the dimensions of enterprise services.
The key to understanding enterprise services is the idea that enterprise services are primarily two things, an interface and an implementation, that are broken into three parts when put into action: the consumer proxy that invokes the service interface; the provider proxy that accepts the invocation of a service, manages the communication with the consumer, and passes the information to the implementation; and the implementation that does the work. Figure 5-4 makes this relationship clear.
Figure 5-4. Enterprise services in consumers and providers
To really understand how all of the parts work together, we will discuss what happens during two phases of design and then look at what happens at runtime.
The first phase to be examined is that of designing an enterprise service. There are ...