A Petri Net Semantics for B ( PN ) 2 with Procedures which Allows

Veriication of parallel programs is a very important goal on the way to improve the reliability of software. The PEP tool, a Programming Environment based on Petri nets, allows veriication of parallel programs by partial order model checking based on a compositional denotational Petri net semantics. The language supported by the PEP tool covers block structuring, parallel and sequential composition, choice, iteration, synchronous and asynchronous communication , including use of unbounded buuers. At present, it does not cover, however, the structuring of programs by procedures. The main contribution of this paper consists in the development of a fully compositional high level Petri net semantics for concurrent programs with procedures, covering recursion, global variables, and many types of parameter passing (including call-by-reference). The semantics will guarantee that the semantical model (HL and LL nets) of program P is nite whenever: P has only nite data types. For each procedure in P only a nitely many instances can be active concurrently. Due to the abstract and exible nature of the Petri net model used, our approach is very general and may also be applied to other speciication and programming languages. This has already (partially) been done for the Speciication and Description Language (SDL).