SOA is necessarily a collection of services. These services communicate with each other. The communication can involve simple data passing, or it could affect two or more services coordinating some activity. Some means of connecting services to each other is needed. Obviously, service-oriented architectures are not a new thing. The first service-oriented architecture for many people in the past was with the use DCOM or Object Request Brokers (ORBs) based on the CORBA specification.

If SOA to be effective, we need a clear understanding of the term service. A service is a function that well-defined, self-contained and does not depend on the context or state of other services.

The technology of Web Services is the most likely connection technology of service-oriented architectures.The service provider returns a response message to the service consumer. Meanwhile, the request and subsequent response connections defined in some way that is understandable to both the service consumer and service provider. In fact how those connections established explained in Web Services. Overall a service provider can also be a service consumer.