A challenge in Web services architectures is to compose basic services to obtain larger applications. Before using a service, a designer must ensure that it is compatible with the needs of the application. This means that inputs and outputs of the service comply with the intended ranges of data in the composite service, but also that the basic service eventually returns a value. In this paper, we address the compatibility problem for composite services described using document-based workflow nets, that can depict the semantics of Active XML (AXML) systems, a document based formalism for
Web services design. The behavior of non-recursive AXML specifications with finite data domains can be represented as Docnets, i.e., finite labeled Petri nets carrying information about document types they transform. We then characterize compatibility of Docnet modules in terms of a decidable reachability property in the underlying net. Finally, we show the distributivity of compatibility over composition, which allows for a faster semi-decision algorithm to verify compatibility between sets of modules.
Keywords: Web services, composition, Active XML, document based workflow.