🗊Презентация SAT and model checking

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Слайды и текст этой презентации


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SAT and Model Checking
Описание слайда:
SAT and Model Checking

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Bounded Model Checking (BMC)
A.I. Planning problems: can we reach a desired state in k steps?
Verification of safety properties: can we find a bad state in k steps?
Verification: can we find a counterexample in k steps ?
Описание слайда:
Bounded Model Checking (BMC) A.I. Planning problems: can we reach a desired state in k steps? Verification of safety properties: can we find a bad state in k steps? Verification: can we find a counterexample in k steps ?

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What is SAT?
Описание слайда:
What is SAT?

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BMC idea
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BMC idea

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BMC idea (cont’d)
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BMC idea (cont’d)

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Safety-checking as BMC
Описание слайда:
Safety-checking as BMC

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Example: a two bit counter
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Example: a two bit counter

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Example: another counter
Описание слайда:
Example: another counter

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What BMC with SAT Can Do
All LTL
ACTL and ECTL
In principle, all CTL and even mu-calculus
efficient universal quantifier elimination or fixpoint computation is an active area of research
Описание слайда:
What BMC with SAT Can Do All LTL ACTL and ECTL In principle, all CTL and even mu-calculus efficient universal quantifier elimination or fixpoint computation is an active area of research

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How big should k be?
For every model M and LTL property  there exists k s.t.
The minimal such k is the Completeness Threshold (CT)
Описание слайда:
How big should k be? For every model M and LTL property  there exists k s.t. The minimal such k is the Completeness Threshold (CT)

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How big should k be?
Diameter d = longest shortest path from an initial state to any other reachable state. 
Recurrence Diameter rd = longest loop-free path.
rd ¸ d
Описание слайда:
How big should k be? Diameter d = longest shortest path from an initial state to any other reachable state. Recurrence Diameter rd = longest loop-free path. rd ¸ d

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How big should k be?
Theorem: for Gp properties CT = d
Описание слайда:
How big should k be? Theorem: for Gp properties CT = d

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How big should k be?
Theorem: for Fp properties CT= rd
Описание слайда:
How big should k be? Theorem: for Fp properties CT= rd

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A basic SAT solver 
Given   in CNF: (x,y,z),(-x,y),(-y,z),(-x,-y,-z)
Описание слайда:
A basic SAT solver Given  in CNF: (x,y,z),(-x,y),(-y,z),(-x,-y,-z)

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SAT and model checking, слайд №15
Описание слайда:

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DPLL-style SAT solvers
Описание слайда:
DPLL-style SAT solvers

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The Implication Graph
Описание слайда:
The Implication Graph

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Resolution
Описание слайда:
Resolution

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Conflict clauses
Описание слайда:
Conflict clauses

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Conflict Clauses (cont.)
Conflict clauses:
Are generated by resolution
Are implied by existing clauses
Are in conflict with the current assignment
Are safely added to the clause set
Описание слайда:
Conflict Clauses (cont.) Conflict clauses: Are generated by resolution Are implied by existing clauses Are in conflict with the current assignment Are safely added to the clause set

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Generating refutations
Refutation = a proof of the null clause
Record a DAG containing all resolution steps performed during conflict clause generation.
When null clause is generated, we can extract a proof of the null clause as a resolution DAG.
Описание слайда:
Generating refutations Refutation = a proof of the null clause Record a DAG containing all resolution steps performed during conflict clause generation. When null clause is generated, we can extract a proof of the null clause as a resolution DAG.

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Unbounded Model Checking
A variety of methods to exploit SAT and BMC for unbounded model checking:
Completeness Threshold
k - induction
Abstraction (refutation proofs useful here)
Exact and over-approximate image computations (refutation proofs useful here)
Use of Craig interpolation
Описание слайда:
Unbounded Model Checking A variety of methods to exploit SAT and BMC for unbounded model checking: Completeness Threshold k - induction Abstraction (refutation proofs useful here) Exact and over-approximate image computations (refutation proofs useful here) Use of Craig interpolation

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Conclusions: BDDs vs. SAT
Many models that cannot be solved by BDD symbolic model checkers, can be solved with an optimized SAT Bounded Model Checker. 
The reverse is true as well.
BMC with SAT is faster at finding shallow errors and giving short counterexamples. 
BDD-based procedures are better at proving absence of errors.
Описание слайда:
Conclusions: BDDs vs. SAT Many models that cannot be solved by BDD symbolic model checkers, can be solved with an optimized SAT Bounded Model Checker. The reverse is true as well. BMC with SAT is faster at finding shallow errors and giving short counterexamples. BDD-based procedures are better at proving absence of errors.

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Acknowledgements
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Acknowledgements



Теги SAT and model checking
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