Formalising Message Exchange Patterns using BPEL Light

In a message-driven SOA, message exchange patterns (MEPs) define a reusable notion of conversational contracts between a service consumer and a service provider from the provider´s point of view. They enable a common understanding regarding a message flow between both parties. In contrast to version 1.1 of the Web Service Description Language (WSDL) the current version 2.0 has introduced a template for defining such patterns that allows to define and reference patterns beyond the standard input/output ones defined in the specification. Although reasonable, this approach brings several disadvantages which we point out in this paper. Since WSDL 2.0 MEPs and WS-BPEL processes describe interaction behaviour from the same perspective BPEL makes a perfect candidate as a language for formalising MEPs, especially because it provides a powerful mechanism for describing control flow and correlation of related messages. In this work we propose a way to formalising MEPs using a WSDL-less BPEL dialect called BPEL light. We introduce a new abstract BPEL profile for defining reusable and machine-readable MEPs that is capable of expressing arbitrary message exchanges. With this approach we pave the way for more flexible interaction styles and reduce the impedance mismatch between imperative programming and message orientation.