Extending CSP: denotational semantics

Modern CSP is an algebra which describes processes which engage in events. Its characteristic comprehensiveness combined with simplicity arises in large part from the fact that it was originally defined by a denotational semantics. This sets it apart from other process algebras. Part of the simplicity of CSP arises from its high level of abstraction. In particular, conventional CSP abstracts from priority. CSP practitioners occasionally find this awkward, particularly when describing real time systems and in hardware compilation. An extension of CSP is introduced which includes priority without compromising simplicity or abstraction. Furthermore, the extension is built by way of a denotational semantics which is in full sympathy with the spirit of CSP. An unexpected merit of the new semantics is that it solves completely some long standing difficulties in describing infinite behaviour with the conventional denotational semantic models for CSP. Furthermore it provides elegant and simple treatments of termination and divergence in contrast to earlier rather awkward approaches.