Explanation/Reference:
In service-oriented integration the consumer is decoupled from the source system via the SOA Service that encapsulates and abstracts the source systems behind a service interface. Consumers of the SOA Service should need no details about the underlying source system. They should base the service usage solely on the contract provided by the SOA Service.
Unfortunately, simply adding a wrapper (e.g. Web service) to an existing system does not eliminate point- to-point integration. In fact point-to-point integration can be accomplished quite nicely using Web service interfaces. To be truly service-oriented, the SOA Services created must be well designed and constructed so the source system details do not bleed through. Service infrastructure that provides capabilities such as service discovery and routing is also essential to decouple service providers and consumers.
Reference: Oracle Reference Architecture, Service-Oriented Integration, Release 3.0