Any developer of discrete event systems knows that the most important quality of the final system is that it be functionally correct by exhibiting certain functionaL or qualitative properties decided upon as being important. Once assured that the system behaves correctly, it is also important that it is efficient in that its running cost is minimal or that it executes in optimum time or whatever performance measure is chosen. While functional correctness is taken for granted, the latter quantitative properties will often decide the success, or otherwise, of the system. Ideally the developer must be able to specify, design and implement his system and test it for both functional correctness and performance using only one for­ malism. No such formalism exists as yet. In recent years the graphical version of the Specification and Description Language (SDL) has become very popular for the specification, design and partial implementation of discrete systems. The ability to test for functional correctness of systems specified in SDL is, however, limited to time consuming simulative executions of the specification and perfor­ mance analysis is not directly possible. Petri nets, although graphical in format are somewhat tedious for specifying large complex systems but, on the other hand were developed exactly to test discrete, distributed systems for functional correctness. With a Petri net specification one can test, e. g. , for deadlock, live­ ness and boundedness of the specified system.