Finding Mode Invariants in SCR Speci cations

This paper introduces an algorithm and a new graph, the Conditioned Transition Graph (CTG), to derive the mode invariants from an Software Cost Reduction (SCR) mode transition table. An SCR requirements document contains a complete description of the external behavior of the software system. Some system properties, such as mode invariants, can be used to describe safety features that must be ensured during software development. Current SCR requirements documents give independently derived invariants. The algorithm detects mode invariants by rst transforming an SCR mode transition table into a CTG, and then applying de ned computations on two matrices derived from the CTG incidence matrix. The algorithm was used to generate mode invariants from an SCR mode transition table, which were correct as compared to externally derived invariants. An SCR requirements document implies some invariant properties of the speci ed system. This method can also be used to provide test requirements and test cases that are independent of the software design structure.