Core BPEL: Semantic Clarification of WS-BPEL 2.0 through Syntactic Simplification using XSL Transformations

The Web Services Business Process Execution Language (WS-BPEL) is a language for expressing business process behaviour based on web services. The language is intentionally not minimal but provides a rich set of constructs, allows omission of constructs by relying on defaults, and supports language extensions. Combined with the fact that the language definition does not provide a formal semantics, it is an arduous task to work formally with the language (e.g. to give an implementation).

In this paper we identify a core subset of the language, called Core BPEL, which has fewer and simpler constructs, does not allow omissions, and does not contain ignorable elements. We do so by identifying syntactic sugar, including default values, and ignorable elements in WS-BPEL. The analysis results in a translation from the full language to the core subset. Thus, we reduce the effort needed for working formally with WS-BPEL, as one, without loss of generality, need only consider the much simpler Core BPEL. This report may also be viewed as an addendum to the WS-BPEL standard specification, which clarifies the WS-BPEL syntax and presents the essential elements of the language in a more concise way.

To make the results of this work directly usable for practical purposes, we provide an XML Schema for Core BPEL and a set of XSLT 1.0 transformations that will transform any standard compliant WS-BPEL process into a Core BPEL process. We also provide an online service where one can apply the transformation.

This work is part of the initial considerations on the implementation of a WS-BPEL engine within the Computer Supported Mobile Adaptive Business Processes (CosmoBiz) research project at the IT University of Copenhagen.