Specification and verification of a safety shell with statecharts and extended timed graphs

A new technique for applying safety principles, termed safety shell, eases the formal verification by segregation of the safety critical regions of the application into independent, well structured modules. This paper presents a practical use of formal methods for verification of the safety shell. A framework is proposed for the integration of semiformal and formal notations, in order to produce a formal specification on which verification tools can be applied. The approach relies on the following steps. The first step consists in using adequately statecharts and support tools to guide the analyst's understanding of the system and produce a preliminary document. In the second step an XTG-based specification is generated from the preliminary document on the basis of predefined rules. The third step then is to verify the specification w.r.t. relevant specified properties. Tool support is being developed to assist in the second step, while tool support for verification is available through the TVS toolset.