On the Construction of Submodule Specifications and Communication Protocols

The problem of elaborating the specification for the submodules of a system is considered. A new method for the construction of submodule specifications is described. If the system is to consist of n submodules and the system as well as (n 1) submodules are specified, then the method described determines the specification of the additional n t h submodule. A formula is given which defines the specification of the additional submodule in the general case where module specifications are given in terms of sets of possible execution sequences, and interaction occurs when several modules participate in the execution of an atomic interaction. For the restricted context of finite-state machines, a constructive algorithm for the evaluation of the formula is given. The use of this design method is demonstrated by examples, including a simple communication protocol involving error detection and retransmission. Possible applications in other areas, as well as remaining problems, are indicated.