Guards, Failure, and Partiality: Dijkstra's Guarded-Command Language Formulated Topologically
نویسنده
چکیده
Existing treatments of Dijkstra’s guarded-command language treat divergence and failure as equivalent, even though Dijkstra clearly states they are not. We reexamine Dijkstra’s language, redefining its denotational semantics with powerdomains formulated in topological terms. The results refine existing work, give a sound semantics of guards, failure, and divergence for non-flat storage domains, and reveal the important role that general topology plays in program correctness.
منابع مشابه
Relational Model for Non-deterministic Programs and Predicate Transfop~iers*
A relational model for non-deterministic programs is presented. Several predicate transformers are introduced and it is shown that one of them satisfies all the healthiness criteria indicated by Dijkstra for a useful total correctness predicate transformer. An axiomatic relational definition of the language of guarded commands is proposed. From it the predicate transformers associated to each c...
متن کاملAn automatic abstraction technique for verifying featured, parameterised systems
A general technique combining model checking and abstraction is presented that allows property based analysis of systems consisting of an arbitrary number of featured components. We show how parameterised systems can be specified in a guarded command form with constraints placed on variables which occur in guards. We prove that results that hold for a small number of components can be shown to ...
متن کاملFormal Aspects of Computing Command Algebras, Recursion and Program Transformation
Dijkstra's language of guarded commands is extended with recursion and transformed into algebra. The semantics is expressed in terms of weakest preconditions and weakest liberal preconditions. Extreme fixed points are used to deal with recursion. Unbounded nondeterminacy is allowed. The algebraic setting enables us to develop efficient transformation rules for recursive procedures. The main res...
متن کاملA Generic Approach for the Automatic Verification of Featured, Parameterised Systems
A general technique is presented that allows property based feature analysis of systems consisting of an arbitrary number of components. Each component may have an arbitrary set of safe features. The components are defined in a guarded command form and the technique combines model checking and abstraction. Features must fulfill certain criteria in order to be safe, the criteria express constrai...
متن کاملThe Weakest Precondition Calculus : Recursion
An extension of Dijkstra's guarded command language is studied, including unbounded demonic choice and a backtrack operator. We consider three orderings on this language: a reenement ordering deened by Back, a new deadlock ordering, and an approximation ordering of Nelson. The deadlock ordering is in between the two other orderings. All operators are monotonic in Nelson's ordering, but backtrac...
متن کامل