Introduction

So far the quiescent trace set of a handshake process was specified in one of the following forms: by enumeration, by a predicate, by a state graph, or by parallel composition of other handshake processes.

For many handshake processes none of the above forms may be convenient. An example of such a process is the process that first behaves like P and then, “after successful termination of P”, behaves like Q. Of course, such sequential composition of the handshake processes P and Q requires a notion of successful termination of a process. A sequential handshake process is a handshake process in which that notion is incorporated.

The aim of this chapter is to develop a model for sequential handshake processes and a calculus for these processes. An important application of this calculus is the description of the handshake components required for the compilation of Tangram. Another application is the semantics of Tangram itself.

Sequential handshake processes

A sequential handshake process is a handshake process, some of whose traces are designated as terminal traces, i.e. traces that lead to successful termination. In a sequential composition these terminal traces can be prefixed to traces of the subsequent sequential handshake process.

Let T denote the set of quiescent traces and let U denote the set of terminal traces of sequential handshake process P. Sets T and U must satisfy a number of conditions, which are introduced informally.