Complexity Issues in Automated Model Revision without Explicit Legitimate State

Existing algorithms for the automated model revision incur an impediment that the designers have to identify the legitimate states of original model. Experience suggests that of the inputs required for model revision, identifying such legitimate states is the most difficult. In this paper, we consider the problem of automated model revision without explicit legitimate states. We note that without the explicit legitimate states, in sonic instances, the complexity of model revision increases substantially (from P to NP-hard). In spite of this, we find that this formulation is relatively complete, i.e., if it was possible to perform model revision with explicit legitimate states then it is also possible to do so without the explicit identification of the legitimate states. Finally, we show if the problem of model revision can be solved with explicit legitimate states then the increased cost of solving it without explicit legitimate states is very small. In summary, the results in this paper identify instances of model revision where the explicit knowledge of legitimate state is beneficial and where it is not very crucial.