A hierarchical graph model of the
نویسنده
چکیده
The problem of developing an adequate formal model for the semantics of programming languages has been under intensive study in recent years. Unlike the area of syntax specification, where adequate models have existed for some time, the area of semantic specification is still in the formative stages. Development of formal semantic models has proceeded along two main lines, lambda-calculus models (e.g., Landin,! Strachey2) and directed graph models (e.g., Narasimhan,3 Floyd4). This paper describes a model for the semantics of programs based on hierarchies of directed graphs. A formal model or theory of the semantics of programming languages must provide descriptions on a number af different levels, much as the theory of context-free grammars provides descriptions of the syntax of programming languages on a number of different levels. At the most general level a semantic theory provides a framework for describing a class of programming languages and investigating the mathematical properties of their formal representations in the model. At this general level the context-free grammar model of syntax has been particularly successful, giving rise to an extensive mathematical theory as well as providing characterizations of specialized syntacticallysimilar classes of languages. One would hope that adequate models of semantics would lead to the same sort of mathematical development and to the classification of semantically-similar programming languages. At a more specific level, a semantic model must provide descriptions of the semantics of particular programming languages, much as a particular contextfree grammar may be used to describe the syntax of a particular programming language. One· would expect the formal specification of the semantics of a programming language to allow conciseness and unambiguity in
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