On the expressiveness of CSP

We define “CSP-like” operational semantics in the context of LTS’s: a severely restricted mode of describing operators which can express every operator of Hoare’s CSP. Furthermore we show that every operator with CSP-like operational semantics can be simulated in CSP with the addition of an exception-throwing operator P ΘA Q in which any occurrence of an event a ∈ A within P hands control to Q . Thus any language, all of whose operators are CSP-like, has a semantics over each of the behavioural models of CSP and a natural theory of refinement. This demonstrates that the extended CSP is a natural language to compile other notations into. We explore the range of possibilities for CSP-like languages, which include the π-calculus as demonstrated in a separate paper [18].