An Experiment on the Validation of a Speci cation by Heterogeneous Formal Means: the Transit Node

For many years, the use of formal development methods has been advocated for the purpose of veriication. It is of rst importance to start from a speciication which actually expresses the requirements for the system to be developed. The work described here was performed in the framework of a case study where several formal speciication techniques, and the corresponding tools, have been used concurrently for validation purposes. During this work, several ambiguities and omissions were discovered in the informal speciication, and several inadequacies and one error were discovered in the formal speciications.