A New Semantics for the Inclusive Converging Gateway in Safe Processes

We propose a new semantics for the inclusive converging gateway (also known as

Or-join

). The new semantics coincides with the intuitive, widely agreed semantics for Or-joins on sound acyclic workflow graphs which is implied, for example, by dead path elimination on BPEL flows. The new semantics also coincides with the block-based semantics as used in BPEL on cyclic graphs that can be composed from sound acyclic graphs, repeat- and while-loops. Furthermore, we display several examples for unstructured workflow graphs for which Or-joins get the desired intuitive semantics. A key insight is that not all situations where two or more Or-joins seem to be mutually dependent (known as ‘vicious circles’) are necessarily symmetric. Many such situations are asymmetric and can be resolved naturally in favor of one of the Or-joins. Still symmetric or almost symmetric situations exist, for which it is not clear what semantics is desirable and which result in a deadlock in our semantics. We show that enabledness of an Or-join in our semantics can be decided in linear time in the size of the workflow graph.