In this paper we combine ideas from workflow processing and database query answering. Tailoring process algebras like Milner’s
Calculus of Communicating Systems (CCS)
to relational dataflow makes them a natural candidate for specifying data-oriented workflows in a declarative way. In addition to the classical evaluation of relational operator trees, the combination with the CCS control structures provides (guarded) alternatives and test-based iterations using recursive process fragment definitions. For the actual atomic constituents of the process, language concepts from the relational world, like queries, but also the use of abstract datatypes, e.g., graphs, can be embedded.
We illustrate the advantages of the approach by an application scenario with remote, heterogeneous sources and Web Services that return their results asynchronously. The presented approach has been implemented in a prototype.