Programming 4GL clients to access industry Web services
Figure 1–2 shows the basic industry Web services architecture, showing how a Progress 4GL client application communicates with a Web service.
As you can see, the client architecture for a Progress 4GL application accessing a Web service mirrors the Web service provider and application server architecture. The additional components on the 4GL client specifically for accessing Web services are indicated in a darker gray. The WSDL file, obtained from the Web service provider describes both the logical and physical interface required by the client to access the Web service. At the logical level, OpenEdge uses the WSDL file to define the client interface (API) required to program calls to Web service operations and to provide support for interpreting those operations at run time.
At the physical level, OpenEdge contains its own SOAP processor to convert between calls to 4GL-defined procedures and SOAP messages understood by the Web service, and it supports both nonsecure HTTP and SSL using its HTTP/S listener to manage the transport of these SOAP messages across the wire.
Once the logical and physical interface to a Web service is known, you can interact with that Web service in the 4GL in a manner very similar to interacting with a session-free AppServer. Many of the same 4GL elements are used to support the same logical functionality. In addition, the OpenEdge and the Progress 4GL provides functionality that allows you to handle the unique requirements of managing a Web service request: