Remote Batch Invocation for Web Services: Document-Oriented Web Services with Object-Oriented Interfaces

The Web service description language defines a service as a procedure whose inputs and outputs are arbitrarily structured XML data values, sometimes called documents. In this paper we argue that document-oriented interfaces can be viewed as batches of calls to finer-grained object-oriented interfaces. Turning this correspondence around, we show that flexible documents can be specified by converting a block of fine-grained object-oriented invocations into a batch document. The statements in the block operate directly on virtual service objects and are composed using sequences, conditionals, and loops. Our system, remote batch invocation for Web services, translates object-oriented interfaces into a WSDL describing batches of calls and vice versa. A wrapper class on the server interprets documents described by the WSDL and dispatches method calls to the appropriate server objects. Clients can use the the service described by the WSDL in three ways: using existing WSDL client generation tools, using a wrapper library, or using a language extension to Java. The result is a powerful infrastructure for Web services that is compatible with existing tools and standards while providing an elegant programming model. We have used our infrastructure to create a Web server wrapper for the Amazon associates Web Service, which shows that remote batches can support a clean object-oriented programming model over a stateless Web service.