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SpecDiff: Differencing LTSs

SpecDiff: Differencing LTSs. Zhenchang Xing * , Jun Sun + , Yang Liu * and Jin Song Dong * * National University of Singapore + Singapore University of Technology and Design. Differencing LTSs? Why ?. Program Behaviors Change!. The Evolution of Specification.

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SpecDiff: Differencing LTSs

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  1. SpecDiff: Differencing LTSs Zhenchang Xing*, Jun Sun+, Yang Liu* and Jin Song Dong* *National University of Singapore +Singapore University of Technology and Design

  2. Differencing LTSs? Why?

  3. Program Behaviors Change!

  4. The Evolution of Specification

  5. An Evolved Concurrent Stack Spec in CSP# A later version Evolve An earlier version

  6. The Differences Lead to Program Fault? The LTS of the later version The LTS of the earlier version

  7. The Application of Partial Order Reduction

  8. A Dinning-Philosophers Spec in CSP# Dinning-Philosophers

  9. “Reduced” States and Transitions? Partial Order Reduction (116 states/248 transitions) NOTE: There is nothing wrong with Spec, and Spec remains unchanged! No Partial Order Reduction (118 states/300 transitions)

  10. The Application of Process Counter Abstraction

  11. A Readers-Writer Lock Spec in CSP# Parameterized Readers-Writer Lock

  12. Recurring Changes as Cutoff Number Increases? Cutoff number = 2 Cutoff number = 4 Cutoff number = 3 NOTE: There is nothing wrong with Spec, and Spec remains unchanged! Cutoff number = 1

  13. Why Do We Want to Differencing LTSs? • Analyzing Changing Program Behaviors • Diagnosing faulty evolution • Evaluating impact of different behavior exploration methods • Revealing behavioral change patterns of parameterized systems • ……

  14. Differencing LTSs? How?

  15. An Overview of Our SpecDiff Approach SpecDiff Architecture Describing program behavior in CSP# specification language Generating the LTSs of CSP# program(s) with PAT Simulator Applying GenericDiff to compare two LTSs Visualization and query-based analysis

  16. Differencing LTSs By GenericDiff • Input: LTSs to be compared • LTS1 and LTS2 • GenericDiff: A generic graph differencing technique • Parsing and quantifying the inputs LTSs • Typed Attributed Graphs (TAGs) • Capturing the graph structure and the matching candidates • PairUpGraph (i.e. a product of two TAGs) • Traversing the model graphs and computing the similarities • Random walk on PairUpGraph • Select an “optimal” matching • Bipartite graph matching • Output: Symmetric difference • One set of matched states and transitions • Two sets of unmatched states and transitions

  17. Analyzing LTS Differences • Merging the two LTSs into a unified LTS • Creating the matched parts of two LTSs • Appending the unmatched states and transitions • Visually inspecting the unified LTS • Normal view of the whole unified LTS • Fragmented views of maximally-connected matched (or unmatched) subgraphs • Searching for change patterns • User-defined queries

  18. Diagnosing Faulty Program Evolution A fragment of the unified LTS of the evolved concurrent stack example (returned by the query searching for “matched states with unmatched same-label transitions”, for example, matched states 6/22 with unmatched push.0.1) Black: matched states/transitions in both LTSs; Green: unmatched states/transitions in the earlier-version LTS; Red: unmatched states/transitions in the later-version LTS The second process pops nothing (pop.1.0) after the first process has pushed an item (push.0.1) into the stack!

  19. SpecDiff? Does it Work?

  20. Tool Support & Usage A short demo of SpecDiff in PAT! http://www.patroot.com Formal Tool Demonstration, ASE’10

  21. Initial Evaluation

  22. How to Scale it Up? • Differencing LTSs “smartly” • Syntactic differences to “guide” the differencing process of large LTSs • Interactive visualization techniques to “select” which part(s) of the LTSs to differentiate • Optimizing SpecDiff implementation • Direct comparison of the internal data structures of LTSs instead of the LTSs renderedin the GUI • Identifying “important” differences • Important differences (e.g. program fault) would be reflected in the differences of small LTSs

  23. Why Not Use Counter Examples? • SpecDiff is complementary to counter-example analysis • Contextual information • Highlighted differences • SpecDiff is useful in other scenarios, such as • Nothing wrong with specification • Specification remains unchanged

  24. Conclusions and Future Work Tool Support & Usage SpecDiff: Differencing LTSs Effectiveness & Applicability Scale it Up!

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