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Recipes for State Space Reduction

Recipes for State Space Reduction. Arend Rensink, University of Twente Dutch Model Checking Day, May 2014. Example (believe it or not): Dining Philosophers. Start configuration. First grab left fork. First grab right fork. Then grab left fork. Then grab right fork. Demo.

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Recipes for State Space Reduction

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  1. Recipes for State Space Reduction Arend Rensink, University of TwenteDutch Model Checking Day, May 2014

  2. Example (believe it or not): Dining Philosophers • Start configuration First grableft fork First grabright fork Then grableft fork Then grabright fork Demo Releaseboth forks Recipes for State Space Reduction

  3. Raise atomicity level: Grab both forks • Suppose we’re not interested in deadlock or starvation • E.g., study average philosopher load under assumption of liveness • Essentially, we want to change the grain of atomicity • Define transactions on top of existing transition system: • recipeleftThenRight() { grab1left; grab2right; }reciperightThenLeft() { grab1right; grab2left; } or even • recipegrabBoth() {choice { grab1left; grab2right; }or { grab1right; grab2left; }} • Intuition • Abstracted system has single (recipe-labelled) transition(only) where original system has terminating trace of recipe Demo Recipes for State Space Reduction

  4. What is this presentation about? • Transition systems can grow very large • Too expensive to generate (time/memory) • Too large to analyse • Countermeasures • State space reduction (partial order, symmetry, …) • Abstraction (collapsing similar states) • Coarse-grained atomicity (doing more in one step) • Context: graph transformation as a modelling formalism • Transformation steps reflect the dynamics of a system • GTSs analysed e.g., through model checking Recipes for State Space Reduction

  5. Recipe semantics • Example: recipe c() { a; b; } • Challenging cases: • Refusal behaviour: recipe c() { try a1;b1 else a2; b2; } • Looping behaviour: recipe c() { alap { a1;b1 } } • Exploration strategy: • Local DFS within recipe body b d a d a a a a c c c c c d b b b b b Recipes for State Space Reduction

  6. Message What are recipes good for? • State space reduction • Coarse-grained transitions • Useful when state space used for further analysis • Performance gain • Quantified rules are evaluated faster Contribution • Atomicity through composition (on top of existing LTS) • Also unbounded behaviour • Compare: action refinement • Combination with refusals (try, as-long-as-possible)   Recipes for State Space Reduction

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