Trace Specifications of Non-Deterministic Multi-Object Modules

The Trace Assertion Method (in short: TAM) is a formal method for abstract specification of interfaces of software modules being designed according to the “information hiding” principle. A trace specification is a “black-box” specification, i.e., it describes only those features of a module that are externally observable. The method was introduced by W. Bartusek and D.L. Parnas some 15 years ago and since then has undergone many modifications. In recent years there has been an increased interest in TAM. Software tools supporting practical usage of TAM for software engineering projects are under development, the method is being tested on different applications, its foundations are being studied. Recent experiments with TAM have showed the need for further study in the case of non-deterministic multi-object modules. In this paper we investigate the expressiveness of the method for such modules. We present a formal model of a module and its TAM specification, show that the method requires some extensions and propose solutions. Our considerations are illustrated on TAM but could also be generally applied to modules with hidden non-determinism. The full version of our investigations, including all definitions, lemmas, proofs and examples, is presented in university technical reports.