11 research outputs found
Automated abstraction by incremental refinement in interpolant-based model checking
Abstract—This paper addresses the field of Unbounded Model
Checking (UMC) based on SAT engines, where Craig interpolants
have recently gained wide acceptance as an automated abstraction
technique.
We start from the observation that interpolants can be quite
effective on large verification instances. As they operate on
SAT-generated refutation proofs, interpolants are very good at
automatically abstract facts that are not significant for proofs.
In this work, we push forward the new idea of generating
abstractions without resorting to SAT proofs, and to accept
(reject) abstractions whenever they (do not) fulfill given adequacy
constraints. We propose an integrated approach smoothly
combining the capabilities of interpolation with abstraction and
over-approximation techniques, that do not directly derive from
SAT refutation proofs.
The driving idea of this combination is to incrementally
generate, by refinement, an abstract (over-approximate) image,
built up from equivalences, implications, ternary and localization
abstraction, then (eventually) from SAT refutation proofs.
Experimental results, derived from the verification of hard
problems, show the robustness of our approach
Partial Quantifier Elimination By Certificate Clauses
We study partial quantifier elimination (PQE) for propositional CNF formulas.
In contrast to full quantifier elimination, in PQE, one can limit the set of
clauses taken out of the scope of quantifiers to a small subset of target
clauses. The appeal of PQE is twofold. First, PQE can be dramatically simpler
than full quantifier elimination. Second, it provides a language for performing
incremental computations. Many verification problems (e.g. equivalence checking
and model checking) are inherently incremental and so can be solved in terms of
PQE. Our approach is based on deriving clauses depending only on unquantified
variables that make the target clauses . Proving redundancy
of a target clause is done by construction of a ``certificate'' clause implying
the former. We describe a PQE algorithm called that employs
the approach above. We apply to generating properties of a
design implementation that are not implied by specification. The existence of
an property means that this implementation is buggy. Our
experiments with HWMCC-13 benchmarks suggest that can be used
for generating properties of real-life designs
Replication and Abstraction: Symmetry in Automated Formal Verification.
This article surveys fundamental and applied aspects of symmetry in system models, and of symmetry reduction methods used to counter state explosion in model checking, an automated formal verification technique. While covering the research field broadly, we particularly emphasize recent progress in applying the technique to realistic systems, including tools that promise to elevate the scope of symmetry reduction to large-scale program verification. The article targets researchers and engineers interested in formal verification of concurrent systems