Common use of Qualitative Reasoning Clause in Contracts

Qualitative Reasoning. Ideally, we would like to have a new value for the convergence attribute of Event-B events. However, this is not currently supported by the Rodin platform. Instead, a new probabilistic attribute is defined for events, with the value is either standard or probabilistic. • Since standard refinement does not maintain probabilistic convergent property, we put a restriction on the development method for almost-certain termination systems in two steps as follows. 1. Establish the model of the systems with various anticipated events 2. While proving convergence properties of events (either standard or probabilistic), we keep the variable and event system the same (i.e. no refinement is allowed). • For probabilistic convergence, the variant need to be bounded above. A combination of standard and probabilistic convergence events results in a probabilistic convergence system. Moreover, the use of anticipated events and refinement allowed us to construct an lexicographic variant by combining the sub-variant at different level of refinements. For probabilistic convergence system, this lexicographic variant need to be bounded above, which require all the sub-variants to be bounded above (not only those variant concern with probabilistic events). More details of our approach is in our report at AVoCS'10 [8] .