The session model for an OpenEdge Web service must match the session model of the AppServer that hosts your application. If you are exposing an existing AppServer application as an OpenEdge Web service, this choice is already made for you. If you are building a new Web service application, choosing a session model for your Web service defines how you structure your application. The choice of session model affects how the AppObject for a Web service is defined in the WSDL, how the WSA manages the Web service at run time, and how the client must access the Web service objects.