139 research outputs found
A Survey of Satisfiability Modulo Theory
Satisfiability modulo theory (SMT) consists in testing the satisfiability of
first-order formulas over linear integer or real arithmetic, or other theories.
In this survey, we explain the combination of propositional satisfiability and
decision procedures for conjunctions known as DPLL(T), and the alternative
"natural domain" approaches. We also cover quantifiers, Craig interpolants,
polynomial arithmetic, and how SMT solvers are used in automated software
analysis.Comment: Computer Algebra in Scientific Computing, Sep 2016, Bucharest,
Romania. 201
A Theory of Sampling for Continuous-time Metric Temporal Logic
This paper revisits the classical notion of sampling in the setting of
real-time temporal logics for the modeling and analysis of systems. The
relationship between the satisfiability of Metric Temporal Logic (MTL) formulas
over continuous-time models and over discrete-time models is studied. It is
shown to what extent discrete-time sequences obtained by sampling
continuous-time signals capture the semantics of MTL formulas over the two time
domains. The main results apply to "flat" formulas that do not nest temporal
operators and can be applied to the problem of reducing the verification
problem for MTL over continuous-time models to the same problem over
discrete-time, resulting in an automated partial practically-efficient
discretization technique.Comment: Revised version, 43 pages
Understanding Cutting Planes for QBFs
We define a cutting planes system CP+8red for quantified Boolean formulas (QBF) and analyse the proof-theoretic strength of this new calculus. While in the propositional case, Cutting Planes is of intermediate strength between resolution and Frege, our findings here show that the situation in QBF is slightly more complex: while CP+8red is again weaker than QBF Frege and stronger than the CDCL-based QBF resolution systems Q-Res and QU-Res, it turns out to be incomparable to even the weakest expansion-based QBF resolution system 8Exp+Res. Technically, our results establish the effectiveness of two lower boun
Bounded variability of metric temporal logic
Deciding validity of Metric Temporal Logic (MTL) formulas is generally very complex and even undecidable over dense time domains; bounded variability is one of the several restrictions that have been proposed to bring decidability back. A temporal model has bounded variability if no more than v events occur over any time interval of length V, for constant parameters v and V. Previous work has shown that MTL validity over models with bounded variability is less complex—and often decidable—than MTL validity over unconstrained models. This paper studies the related problem of deciding whether an MTL formula has intrinsic bounded variability, that is whether it is satisfied only by models with bounded variability. The results of the paper are mainly negative: over dense time domains, the problem is mostly undecidable (even if with an undecidability degree that is typically lower than deciding validity); over discrete time domains, it is decidable with the same complexity as deciding validity. As a partial complement to these negative results, the paper also identifies MTL fragments where deciding bounded variability is simpler than validity, which may provide for a reduction in complexity in some practical cases
Reasoning About the Transfer of Control
We present DCL-PC: a logic for reasoning about how the abilities of agents
and coalitions of agents are altered by transferring control from one agent to
another. The logical foundation of DCL-PC is CL-PC, a logic for reasoning about
cooperation in which the abilities of agents and coalitions of agents stem from
a distribution of atomic Boolean variables to individual agents -- the choices
available to a coalition correspond to assignments to the variables the
coalition controls. The basic modal constructs of DCL-PC are of the form
coalition C can cooperate to bring about phi. DCL-PC extends CL-PC with dynamic
logic modalities in which atomic programs are of the form agent i gives control
of variable p to agent j; as usual in dynamic logic, these atomic programs may
be combined using sequence, iteration, choice, and test operators to form
complex programs. By combining such dynamic transfer programs with cooperation
modalities, it becomes possible to reason about how the power of agents and
coalitions is affected by the transfer of control. We give two alternative
semantics for the logic: a direct semantics, in which we capture the
distributions of Boolean variables to agents; and a more conventional Kripke
semantics. We prove that these semantics are equivalent, and then present an
axiomatization for the logic. We investigate the computational complexity of
model checking and satisfiability for DCL-PC, and show that both problems are
PSPACE-complete (and hence no worse than the underlying logic CL-PC). Finally,
we investigate the characterisation of control in DCL-PC. We distinguish
between first-order control -- the ability of an agent or coalition to control
some state of affairs through the assignment of values to the variables under
the control of the agent or coalition -- and second-order control -- the
ability of an agent to exert control over the control that other agents have by
transferring variables to other agents. We give a logical characterisation of
second-order control
Early validation of system requirements and design
Dissertação de mestrado em Engenharia InformáticaModern society is relying more and more on electronic devices, most of which are em bedded systems and are sometimes responsible for performing safety-critical tasks. As
the complexity of such systems increases due to concurrency concerns and real-time con straints, their design is more prone to errors which can lead to catastrophic outcomes.
In order to reduce the risk of such outcomes, a model-based methodology is commonly
used. The model describes the behaviour of the system and is subject to verification tech niques such as simulation and model checking in order to verify it behaves according to
the requirements. Common problems that arise with this methodology is the ambiguity of
requirements written in natural language and the translation of a requirement to a property
that can be verified along with the model.
This thesis proposes a tool that, after the translation of the requirements to temporal
formalism, allows the automatic generation of monitors in order to verify the model. Our
target platform is Simulink, which is widely used in this domain to model, simulate and
analyze dynamic systems.A sociedade de hoje depende cada vez mais de dispositivos eletrónicos, a maioria dos quais
são sistemas embebidos e, por vezes, responsáveis pela realização de tarefas críticas. À
medida que a complexidade destes sistemas aumenta devido a problemas de concorrência
ou restrições de tempo real, o design torna-se mais suscetível a erros que podem levar a
resultados catastróficos. A fim de reduzir estes riscos, recorre-se a uma metodologia de
desenvolvimento baseada em modelos. O modelo descreve o comportamento do sistema e
pode ser sujeito a técnicas de verificação, tais como simulação ou model checking, a fim de
verificar que este exibe o comportamento descrito nos requisitos. Problemas comuns que
surgem com esta metodologia devem-se a ambiguidade dos requisitos, tipicamente escritos
em linguagem natural, e a tradução destes para uma propriedade que pode ser verificada
em conjunto com o modelo.
Esta dissertação propõe uma ferramenta que, após a tradução dos requisitos para uma linguagem de especificação formal, permite a geração automática de monitores para verificar o modelo. A plataforma para a qual os monitores são gerados e o Simulink, que é
tipicamente utilizado neste domínio para modelar, simular e analisar sistemas dinâmicos
Building Strategies into QBF Proofs
Strategy extraction is of great importance for quantified Boolean formulas (QBF), both in solving and proof complexity. So far in the QBF literature, strategy extraction has been algorithmically performed from proofs. Here we devise the first QBF system where (partial) strategies are built into the proof and are piecewise constructed by simple operations along with the derivation. This has several advantages: (1) lines of our calculus have a clear semantic meaning as they are accompanied by semantic objects; (2) partial strategies are represented succinctly (in contrast to some previous approaches); (3) our calculus has strategy extraction by design; and (4) the partial strategies allow new sound inference steps which are disallowed in previous central QBF calculi such as Q-Resolution and long-distance Q-Resolution. The last item (4) allows us to show an exponential separation between our new system and the previously studied reductionless long-distance resolution calculus. Our approach also naturally lifts to dependency QBFs (DQBF), where it yields the first sound and complete CDCL-style calculus for DQBF, thus opening future avenues into CDCL-based DQBF solving
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