Service Oriented Architecture (SOA) 

A service-oriented architecture (SOA) is essentially a collection of services. These services communicate with each other. The communication can involve either simple data passing or it could involve two or more services coordinating some activity. Some means of connecting services to each other is needed.

A service is a function that is well-defined, self-contained, and does not depend on the context or state of other services.

The communication basically works in the way that a service consumer sends a service request message to a service provider. The service provider returns a response message to the service consumer. The request and subsequent response connections are defined in some way that is understandable to both the service consumer and service provider. The connection are defined by Web services. A service provider can also be a service consumer.