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Gabmeyer S.,TU Darmstadt | Seidl M.,Institute for Formal Models and Verification
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2016

We present a novel symbolic bounded model checking approach to test reachability properties of model-driven software implementations. Given a concrete initial state of a software system, a type graph, and a set of graph transformations, which describe the system’s structure and its behavior, the system is tested against a reachability property that is expressed in terms of a graph constraint. Without any user intervention, our approach exploits state-of-the-art model checking technologies successfully used in hardware industry. The efficiency of our approach is demonstrated in two case studies. © Springer International Publishing Switzerland 2016.


Lonsing F.,Vienna University of Technology | Egly U.,Vienna University of Technology | Seidl M.,Institute for Formal Models and Verification
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2016

Q-resolution is a proof system for quantified Boolean formulas (QBFs) in prenex conjunctive normal form (PCNF) which underlies search-based QBF solvers with clause and cube learning (QCDCL). With the aim to derive and learn stronger clauses and cubes earlier in the search, we generalize the axioms of the Q-resolution calculus resulting in an exponentially more powerful proof system. The generalized axioms introduce an interface of Q-resolution to any other QBF proof system allowing for the direct combination of orthogonal solving techniques. We implemented a variant of the Q-resolution calculus with generalized axioms in the QBF solver DepQBF. As two case studies, we apply integrated SAT solving and resource-bounded QBF preprocessing during the search to heuristically detect potential axiom applications. Experiments with application benchmarks indicate a substantial performance improvement. © Springer International Publishing Switzerland 2016.


Kiesl B.,Vienna University of Technology | Seidl M.,Institute for Formal Models and Verification | Tompits H.,Vienna University of Technology | Biere A.,Institute for Formal Models and Verification
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2016

In theory and practice of modern SAT solving, clauseelimination procedures are essential for simplifying formulas in conjunctive normal form (CNF). Such procedures identify redundant clauses and faithfully remove them, either before solving in a preprocessing phase or during solving, resulting in a considerable speed up of the SAT solver. A wide number of effective clause-elimination procedures is based on the clause-redundancy property called blocked clauses. For checking if a clause C is blocked in a formula F, only those clauses of F that are resolvable with C have to be considered. Hence, the blocked-clauses redundancy property can be said to be local. In this paper, we argue that the established definitions of blocked clauses are not in their most general form. We introduce more powerful generalizations, called setblocked clauses and super-blocked clauses, respectively. Both can still be checked locally, and for the latter it can even be shown that it is the most general local redundancy property. Furthermore, we relate these new notions to existing clause-redundancy properties and give a detailed complexity analysis. © Springer International Publishing Switzerland 2016.


Lonsing F.,Vienna University of Technology | Bacchus F.,University of Toronto | Biere A.,Institute for Formal Models and Verification | Egly U.,Vienna University of Technology | Seidl M.,Institute for Formal Models and Verification
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2015

Among preprocessing techniques for quantified Boolean formula (QBF) solving, quantified blocked clause elimination (QBCE) has been found to be extremely effective.We investigate the power of dynamically applying QBCE in search-based QBF solving with clause and cube learning (QCDCL). This dynamic application of QBCE is in sharp contrast to its typical use as a mere preprocessing technique. In our dynamic approach, QBCE is applied eagerly to the formula interpreted under the assignments that have been enumerated in QCDCL. The tight integration of QBCE in QCDCL results in a variant of cube learning which is exponentially stronger than the traditional method.We implemented our approach in the QBF solver DepQBF and ran experiments on instances from the QBF Gallery 2014. On application benchmarks, QCDCL with dynamic QBCE substantially outperforms traditional QCDCL. Moreover, our approach is compatible with incremental solving and can be combined with preprocessing techniques other than QBCE. © Springer-Verlag Berlin Heidelberg 2015.


Kaufmann P.,Vienna University of Technology | Kronegger M.,Vienna University of Technology | Pfandler A.,Vienna University of Technology | Seidl M.,Vienna University of Technology | And 2 more authors.
CEUR Workshop Proceedings | Year: 2013

We present a novel propositional encoding for the reachability problem of communicating state machines. The problem deals with the question whether there is a path to some combination of states in a state machine view starting from a given configuration. Reachability analysis finds its application in many verification scenarios. By using an encoding inspired by approaches to encode planning problems in artificial intelligence, we obtain a compact representation of the reachability problem in propositional logic. We present the formal framework for our encoding and aprototype implementation. A first case study underpins its effectiveness.


Bill R.,Vienna University of Technology | Gabmeyer S.,Vienna University of Technology | Kaufmann P.,Vienna University of Technology | Seidl M.,Institute for Formal Models and Verification
CEUR Workshop Proceedings | Year: 2014

We present the model checker MocOCL, a tool for model checking software models. The design rationale behind MocOCL is to close the gap between formal verification based on model checking and model-based engineering. Our approach avoids conversions that translate the software models into a format that a model checker can process. To this end, we implemented an explicit state model checker that directly processes the software model and verifies them against a specification formulated in a temporal extension of the constraint language OCL. MocOCL offers a web interface that interacts with the Eclipse Modeling Framework.


Heule M.J.H.,University of Texas at Austin | Seidl M.,Institute for Formal Models and Verification | Biere A.,Institute for Formal Models and Verification
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2014

For quantified Boolean formulas (QBFs), preprocessing is essential to solve many real-world formulas. The application of a preprocessor, however, prevented the extraction of proofs for the original formula. Such proofs are required to independently validate correctness of the preprocessor's rewritings and the solver's result. Especially for universal expansion proof checking was not possible so far. In this paper, we introduce a unified proof system based on three simple and elegant quantified resolution asymmetric tautology (QRAT) rules. In combination with an extended version of universal reduction, they are sufficient to efficiently express all preprocessing techniques used in state-of-the-art preprocessors including universal expansion. Moreover, these rules give rise to new preprocessing techniques. We equip our preprocessor bloqqer with QRAT proof logging and provide a proof checker for QRAT proofs. © 2014 Springer International Publishing Switzerland.


Heule M.J.H.,University of Texas at Austin | Seidl M.,Institute for Formal Models and Verification | Biere A.,Institute for Formal Models and Verification
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2015

We recently introduced a new proof system for Quantified Boolean Formulas (QBF), called QRAT, that opened up a variety of new preprocessing techniques. This paper presents a concept that follows from the QRAT proof system: blocked literals. Blocked literals are redundant universal literals that can be removed or added to clauses. We show that blocked literal elimination (BLE) and blocked literal addition are not confluent.We implemented BLE in the state-of-the-art preprocessor bloqqer. Our experimental results illustrate that the BLE extension improves solver performance on the 2014 QBF evaluation benchmarks. © Springer International Publishing Switzerland 2015.


Heule M.J.H.,University of Texas at Austin | Biere A.,Institute for Formal Models and Verification
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2015

Many hard-combinatorial problems have only be solved by SAT solvers in a massively parallel setting. This reduces the trust one has in the final result as errors might occur during parallel SAT solving or during partitioning of the original problem. We present a new framework to produce clausal proofs for cube-and-conquer, arguably the most effective parallel SAT solving paradigm for hard-combinatorial problems. The framework also provides an elegant approach to parallelize the validation of clausal proofs efficiently, both in terms of run time and memory usage. We evaluate the presented approach on some hard-combinatorial problems and validate constructed clausal proofs in parallel. © Springer-Verlag Berlin Heidelberg 2015.


Seidl M.,Institute for Formal Models and Verification | Konighofer R.,Graz University of Technology
Proceedings -Design, Automation and Test in Europe, DATE | Year: 2014

For effectively solving quantified Boolean formulas (QBFs), preprocessors have shown to be of great value. A preprocessor rewrites a formula such that helpful information is made explicit and irrelevant information is removed. For this purpose, techniques, which would be too costly when repeatedly applied during the solving process, are used. Unfortunately, most preprocessing techniques are not model preserving and therefore incompatible with certification frameworks. In consequence, the application of a preprocessor prohibits the extraction of witnesses encoding a solution or a counterexample of a formula. In this paper, we show how to obtain partial witnesses from preprocessed QBFs. Partial witnesses are assignments for the variables of the outermost quantifier block and are extensible to full witnesses, which are usually represented as functions reflecting the dependencies between variables. For many applications, however, partial witnesses are sufficient. We modified the publicly available preprocessor bloqqer for extracting partial witnesses. We empirically compare the effectiveness of the modified and the original version of bloqqer. Further, we apply the new version of bloqqer for solving hardware synthesis problems for which it turns out to be extremely beneficial. © 2014 EDAA.

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