An operational semantics of multitasking and exception handling in Ada

Considerable interest has been generated within the computer science community by the problem of the semantics of the language Ada, especially that part of the semantics which is concerned with multitasking and exception handling (see [Bjørner and Oest 80], [Luckham and Polak 80],[Hennessy and Li 81]). The purpose of this paper is to give an operational semantics for multitasking and exception handling in Ada using a structural approach. To focus our attention on the above features, we first carefully select a small subset of Ada called Ada.1 which is obtained from Dijkstra's guarded command language ([Dijkstra 76]) by adding constructs concerned with multitasking. We then define an operational semantics for it. Adding new constructs concerned with exceptions into Ada.1 we get a new subset called Ada.2 and study how the semantics of the exception mechanism can be handled by labelled transition relations.