Release 10.1A: OpenEdge Getting Started:
OpenEdge Reference Architecture

Service interfaces

In the OpenEdge RA, the Presentation Layer and the Integration Layer must communicate with components in the Business Servicing Layer. The OpenEdge RA is a Service Oriented Architecture (SOA) because it treats components as service providers (components in the Business Servicing Layer) and service requestors (components in the Presentation and Integration Layers). Communication is accomplished through a service interface.

A service interface is an API that publishes the functionality available from business entities. A service interface component is a physical component (such as a Progress .p file) that actually implements the service interface. A proxy or service adapter is a component on the client side of the request (that is, a component of the Presentation or Integration Layers) that interacts with the service interface.

You could have several different service interfaces for the same business component to allow access via different technologies. For example, suppose you want to access stock quotes from an external vendor. A service interface for a .NET client would provide access to stock quotes. A service interface for a Progress 4GL client would provide access to the same stock quotes. In other words, you would create two service interfaces, one for each client type.