On the Introduction of Exceptions in E-LOTOS

Hubert Garavel and Mihaela Sighireanu

Proceedings of the Joint International Conference on Formal Description Techniques for Distributed Systems and Communication Protocols, and Protocol Specification, Testing, and Verification FORTE/PSTV'96 (Kaiserslautern, Germany), pages 469-484, October 1996


The advantages of exception handling are well-known and several sequential or parallel programming languages provide exception handling mechanisms. Unfortunately, none of the three standardized Formal Description Techniques (ESTELLE, LOTOS, and SDL) supports exceptions.
In 1992, Quemada and Azcorra pointed out the need for structuring protocol descriptions with exceptions and proposed to extend LOTOS with a so-called ``generalized termination and enabling'' mechanism.
In this paper, we show that their proposal is not fully appropriate for a compositional description of complex systems. We propose a simpler exception mechanism for LOTOS, for which we provide a syntactic and semantic definition. We show that this exception mechanism is very primitive, as it allows several existing LOTOS operators to be expressed as special cases. We also suggest additional operators, such as symmetric sequential composition and iteration, which can be derived from the exception mechanism.

16 pages