Some topics in the design of the specification language lotos
The definition of Formal Description Techniques is currently being worked out by computer communications standardization bodies in order to produce unambiguous, clear, concise and implementation independent specifications of services and protocols for Open Systems Interconnection (OSI). This paper explores some topics under discussion in the design of one of such techniques, the Language for Temporal Ordering Specification (LOTOS), which has been already used for trial specifications of rather complex protocols and services, though still lacking some essential features like value specification facilities. The language elements rely upon the concepts of synchronized communication events, non deterministic choice between alternative events, value passing, guarding, sequential and parallel composition of processes, process abstraction. Some concepts currently under consideration are argued to be notational variants of the defined language elements; some of them can effectively favour both conciseness and clarity of specification for the intended use of the language. Functional and type abstraction are discussed for what concerns the needed value specification facilities. The addressed topics are illustrated by examples drawn from experience with trial specifications.
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