Java Web Services: Up and Running, 2nd Edition

Web Services and Service-Oriented Architecture

Web services and SOA are related but distinct. SOA, like REST, is more an architectural style—indeed, a mindset—than a body of precisely defined rules for the design and implementation of distributed systems; web services are a natural, important way to provide the services at the core of any SOA system. A fundamental idea in SOA is that an application results from integrating network-accessible services, which are interoperable because each has an interface that clearly defines the operations encapsulated in the service. Per operation, the interface specifies the number and type of each argument passed to the service operation together with the number and type of values returned from each service operation. The very point of a service interface is to publish the invocation syntax of each operation encapsulated in the service. One attraction of the SOA approach is that the ultimate building blocks of even large, complicated systems are structurally simple components; this simplicity at the base level makes it relatively easy to test, debug, deploy, extend, and otherwise maintain a software system.

In an SOA system, services as building block components may be characterized as unassociated and loosely coupled. Consider, for example, two primitive services, S₁ and S₂, in an SOA application. The two services are unassociated in that neither S₁ nor S₂ depends on the other: S₁ is not required to use S₂ or vice versa. The services are mutually ...