lec40-ctl-mc.pdf

# lec40-ctl-mc.pdf - BITS Pilani Pilani Campus MODULE...

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BITS Pilani Pilani Campus MODULE: TEMPORAL LOGICS CTL Semantics and Model Checking Sundar B. CS&IS, BITS Pilani 0 29-11-2016 CS/IS F214 Logic in Computer Science

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CTL Model Checking: Input Simplification Before we look at a model checking algorithm, we simplify the syntax of the input formulas by using an adequate set of operators : [Propositional:] and [Temporal:] AF , EU , and EX . We will assume that the following equivalences are used in order to rewrite the input formula: 1) (AF  ) EG 2) (EF  ) AG 3) E[T U ] EF 4) (EX  ) AX 5) (E[  U (   )] EG  ) A[ U ] 29-11-2016 1 Sundar B. CS&IS, BITS Pilani Eliminate EG and AG Eliminate EF Eliminate AX Eliminate AU
CTL Semantics Evaluation of Formulas Evaluation of a formula would require checking all paths until a universally (or existentially) quantified formula is falsified (or satisfied respectively) in one path or all paths are exhausted. Should the model-checking algorithm generate all paths at once ? i.e. 1. generate all paths in M and store in PATHS 2. for each in PATHS { evaluate in } This is not necessary because evaluation may not be necessary in all paths! 29-11-2016 2 Sundar B. CS&IS, BITS Pilani

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CTL - Automating Evaluation of Formulas Should the evaluation algorithm generate one path at a time and evaluate the formula in that path ? i.e. repeat generate a path and evaluate in until ( there are no more paths ) Issue: each path is infinite and evaluating in one path may not terminate!
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