Nets, Terms and Formulas: Three Views of Concurrent Processes and their Relationship (Cambridge Tracts in Theoretical Computer Science, Series Number 23)

The author presents a theory of concurrent processes where three different semantic description methods that are usually studied in isolation are brought together. Petri nets describe processes as concurrent and interacting machines; algebraic process terms describe processes as abstract concurrent processes; and logical formulas specify the intended communication behaviour of processes. At the heart of this theory are two sets of transformation rules for the top-down design of concurrent processes. The first set can be used to transform stepwise logical formulas into process terms, whilst process terms can be transformed into Petri nets by the second set. These rules are based on novel techniques for the operational and denotational semantics of concurrent processes. Various results and relationships between nets, terms and formulas starting with formulas and illustrated by examples. The use of transformations is demonstrated in a series of case studies, and the author also identifies directions for research. The author presents a theory whereby nets, terms and formulas represent concurrent process at three levels of abstractions: Petri nets are used to describe all details of the operational machine behavior of processes. Algebraic process terms such as Calculus of Communicating Systems (CCS) or Communicating Sequential Processes (CSP) two of the main models for parallel programming, are used to describe the architecture of processes, i.e. how they can be composed from subprocesses. Logical formulas of a first-order trace logic are used to describe the safety and liveness aspects of the communication behavior of processes as required by their users. The main emphasis and technical contribution of this theory are transformations for a top-down design of concurrent processes starting with formulas and proceeding through terms to nets. Many computing systems consist of a possibly large number of components that not only work independently or concurrently, but also interact or communicate with each other from time to time.