The heart of any Web service is the business logic that runs on an application server (as shown in Figure 19). Web service support exists for many existing application server platforms, and new application server platforms dedicated to supporting Web services are also available. Existing server applications can often be packaged as Web services with little or no modification to application code. For example, existing server applications written in Microsoft C# can be supported as C#.NET Web services using ASP.NET. Similarly, Java server applications based on Enterprise Java Beans (EJBs) are often supported as Web services by vendors of Java Servlet Engines (JSEs) using Java servlets to implement both the SOAP processing and interface to the EJB application. Thus, the EJB application might run also as a Java servlet on the Web server, in a separate JVM local to the Web server, or on a separate machine that hosts the application on a network in n-tier fashion.

In all cases, Web services provide some gateway between SOAP and the application server interface (the SOAP processor and business interface shown in Figure 19). This gateway translates Web service messages between SOAP and the interface for the business function supported by the server application. Therefore, the OpenEdge Web services tools provide equivalent support to create Web services from both new and existing AppServer applications.