A service is a function that is 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. Web services essentially use XML to create a robust connection.
The following figure illustrates a basic service-oriented architecture. It shows a service consumer at the right sending a service request message to a service provider at the left. 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. A service provider can also be a service consumer.