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.
