Programming WCF Services, 3rd Edition

Service Contract Factoring and Design

Syntax aside, how do you go about designing service contracts? How do you know which operations to allocate to which service contract? How many operations should each contract have? Answering these questions has little to do with WCF and a lot to do with abstract service-oriented analysis and design. An in-depth discussion of how to decompose a system into services and how to discover contract methods is beyond the scope of this book. Nonetheless, this section offers a few pieces of advice to guide you in your service contracts design effort.

Contract Factoring

A service contract is a grouping of logically related operations. What constitutes “logically related” is usually domain-specific. You can think of service contracts as different facets of some entity. Once you have identified (after requirements analysis) all the operations the entity supports, you need to allocate those operations to contracts. This is called service contract factoring. When you factor a service contract, always think in terms of reusable elements. In a service-oriented application, the basic unit of reuse is the service contract. Ask yourself, will this particular contract factoring yield contracts that other entities in the system can reuse? What facets of the entity can logically be factored out and used by other entities?

As a concrete yet simple example, suppose you wish to model a dog service. The requirements are that the dog should be able to bark and fetch, that ...