La recerca del nostre grup "Lògica i Programació" s'emmarca en el desenvolupament de tècniques i eines per a l'aplicació de la lògica a la resolució de sistemes de restriccions. Més concretament, les principals línies de la nostra investigació es basen per una banda en (a) l'estudi de mètodes de resolució de problemes mitjançant resolvedors de satisfactibilitat proposicional (SAT), de satisfactibilitat mòdul teories (SMT), de programació amb restriccions (CP), i d'extensions d'aquests a optimització (Max-SAT, Max-SMT); i (b) per una altra en l'aplicació d'aquests mètodes per atacar problemes complexos d'interès pràctic, com ara de planificació industrial o d'anàlisis de programes. Mentre que la recerca de tipus més teòric és presentada a les conferències i revistes internacionals de més prestigi de les respectives àrees, els resultats en la vessant més pràctica es materialitzen en transferència de tecnologia en empreses tant de dins com de fora de Catalunya.

The group carries out research in basic computer science. In particular, it has internationally-recognised expertise in the (closely related) fields of logic in computer science, computational complexity and constraint-solving problems, and in the use of advanced programming techniques (e.g. constraint programming, automated deduction, etc.) for the development of practical software tools.

In what follows, we give a brief overview of these research lines. Logic has been called "the calculus of computer science", because its role in computer science is similar to that of mathematics in the physical sciences (see, for example, www.cs.rice.edu/~vardi/logic).

Similarly to the way in which architects and engineers analyse their designs mathematically, computer scientists use logic to analyse systems¿ properties (e.g. correctness, safety and security), during all the phases of their life cycles (e.g. specification, development, verification and maintenance). Also, for systems whose efficiency is critical, logic-based analysis can be very helpful, and in all kinds of systems, logic-based techniques help to reduce costs (see, for example, the section on software productivity tools at research.microsoft.com). Hence, it is not surprising that there is an increasing tendency to use logic-based formalisms in all kinds of hardware and software systems and their components, such as databases or programming languages, among others.

Computational complexity involves the study of the resources required during computation to solve a given problem. The most common resources are time (number of computation steps) and space (amount of memory). Other resources can also be considered, such as randomness (how randomness can increase efficiency) and parallelism (how the use of parallel processors can help). Today, the connections between logic and complexity are well established. For example, the field of proof complexity involves the study of the mathematical relationships between complexity classes (i.e. classes of problems that are solvable using the same amount of resources) and the length of proofs in certain logical systems. This field arose as an approach to the well-known problem of whether the P class of problems equals the NP class or not (see the million-dollar prizes at www.claymath.org): if one could show that, for every propositional proof system, there is a class of tautologies with no short proofs, then the answer is negative. The study of the limitations of proof systems has also led to the discovery of important new algorithms.

Constraint programming is the study of computational systems based on constraints. It has recently emerged as an area of research that engages researchers from a variety of fields. The idea is to solve problems by stating constraints (i.e. conditions, properties) that must be satisfied by the solution. Constraint programming consists of the generation of requirements (constraints) and the solution of these requirements by specialised constraint solvers. It has been successfully applied in numerous domains, including computer graphics (to express geometric coherence), natural language processing (to construct efficient parsers), database systems (to ensure and/or restore the consistency of the data), operations research (optimisation problems), molecular biology (DNA sequencing), business applications (option trading), electrical engineering (to locate faults), circuit design (to compute layouts), etc. Most, if not all, of these practical problems fall into the complexity class of NP-complete problems, for which proof complexity results give insight into classes of deterministic algorithms.

The research group will continue to carry out research in logic-based methods in the areas of automated deduction, rewriting, constraint/logic programming, hardware and software verification, and symbolic computation. For constraint-satisfaction problems and algorithms for combinatorial optimisation problems, the group will also continue to work on aspects such as heuristics, symmetries, and valued constraints, and carry out research in the field of proof and circuit complexity and its close relationship with automated theorem-proving and the satisfiability problem.

Specific tools that are being developed and maintained include automated deduction systems for first-order logic, efficient decision procedures for decidable logics of interest, environments for automated termination proofs, and environments for program verification. Moreover, the research group will continue to apply such tools to circuit verification, industrial planning/scheduling, the Semantic Web, and education, and to pursue their free distribution throughout the Internet.

New research lines of particular interest include the forthcoming Semantic World Wide Web and its associated description logics for semantic search criteria, consistency/integrity restrictions, etc. Another example is the crucial need for logic-based techniques for the verification of cryptographic protocols, in applications such as secrecy, electronic signatures, and electronic money (since testing is useless against malicious attackers). From a more theoretical point of view, we intend to open new lines of research in quantum computing, cryptography, data compression, and applications of game theory to computer science.

All the members of the group have international experience, some as researchers, lecturers and guest lecturers at international institutions. This facilitates close relationships with prestigious institutions, such as the Institute for Advanced Study in Princeton (USA), the DIMACS Research Centre at Rutgers University (USA), the University of Toronto (Canada), the University of California at San Diego (USA), the Max-Planck-Institut for Computer Science (Germany), the École Normale Superieure (France), the École Polytechnique (France), etc.

The group carries out research in basic computer science. In particular, it has internationally-recognised expertise in the (closely related) fields of logic in computer science, computational complexity and constraint-solving problems, and in the use of advanced programming techniques (e.g. constraint programming, automated deduction, etc.) for the development of practical software tools.

In what follows, we give a brief overview of these research lines. Logic has been called "the calculus of computer science", because its role in computer science is similar to that of mathematics in the physical sciences (see, for example, www.cs.rice.edu/~vardi/logic).

Similarly to the way in which architects and engineers analyse their designs mathematically, computer scientists use logic to analyse systems¿ properties (e.g. correctness, safety and security), during all the phases of their life cycles (e.g. specification, development, verification and maintenance). Also, for systems whose efficiency is critical, logic-based analysis can be very helpful, and in all kinds of systems, logic-based techniques help to reduce costs (see, for example, the section on software productivity tools at research.microsoft.com). Hence, it is not surprising that there is an increasing tendency to use logic-based formalisms in all kinds of hardware and software systems and their components, such as databases or programming languages, among others.

Computational complexity involves the study of the resources required during computation to solve a given problem. The most common resources are time (number of computation steps) and space (amount of memory). Other resources can also be considered, such as randomness (how randomness can increase efficiency) and parallelism (how the use of parallel processors can help). Today, the connections between logic and complexity are well established. For example, the field of proof complexity involves the study of the mathematical relationships between complexity classes (i.e. classes of problems that are solvable using the same amount of resources) and the length of proofs in certain logical systems. This field arose as an approach to the well-known problem of whether the P class of problems equals the NP class or not (see the million-dollar prizes at www.claymath.org): if one could show that, for every propositional proof system, there is a class of tautologies with no short proofs, then the answer is negative. The study of the limitations of proof systems has also led to the discovery of important new algorithms.

Constraint programming is the study of computational systems based on constraints. It has recently emerged as an area of research that engages researchers from a variety of fields. The idea is to solve problems by stating constraints (i.e. conditions, properties) that must be satisfied by the solution. Constraint programming consists of the generation of requirements (constraints) and the solution of these requirements by specialised constraint solvers. It has been successfully applied in numerous domains, including computer graphics (to express geometric coherence), natural language processing (to construct efficient parsers), database systems (to ensure and/or restore the consistency of the data), operations research (optimisation problems), molecular biology (DNA sequencing), business applications (option trading), electrical engineering (to locate faults), circuit design (to compute layouts), etc. Most, if not all, of these practical problems fall into the complexity class of NP-complete problems, for which proof complexity results give insight into classes of deterministic algorithms.

The research group will continue to carry out research in logic-based methods in the areas of automated deduction, rewriting, constraint/logic programming, hardware and software verification, and symbolic computation. For constraint-satisfaction problems and algorithms for combinatorial optimisation problems, the group will also continue to work on aspects such as heuristics, symmetries, and valued constraints, and carry out research in the field of proof and circuit complexity and its close relationship with automated theorem-proving and the satisfiability problem.

Specific tools that are being developed and maintained include automated deduction systems for first-order logic, efficient decision procedures for decidable logics of interest, environments for automated termination proofs, and environments for program verification. Moreover, the research group will continue to apply such tools to circuit verification, industrial planning/scheduling, the Semantic Web, and education, and to pursue their free distribution throughout the Internet.

New research lines of particular interest include the forthcoming Semantic World Wide Web and its associated description logics for semantic search criteria, consistency/integrity restrictions, etc. Another example is the crucial need for logic-based techniques for the verification of cryptographic protocols, in applications such as secrecy, electronic signatures, and electronic money (since testing is useless against malicious attackers). From a more theoretical point of view, we intend to open new lines of research in quantum computing, cryptography, data compression, and applications of game theory to computer science.

All the members of the group have international experience, some as researchers, lecturers and guest lecturers at international institutions. This facilitates close relationships with prestigious institutions, such as the Institute for Advanced Study in Princeton (USA), the DIMACS Research Centre at Rutgers University (USA), the University of Toronto (Canada), the University of California at San Diego (USA), the Max-Planck-Institut for Computer Science (Germany), the École Normale Superieure (France), the École Polytechnique (France), etc.

Envíos recientes

  • Choosing the root of the tree decomposition when solving WCSPs: preliminary results 

    Petrova, Aleksandra; Larrosa Bondia, Francisco Javier; Rollón Rico, Emma (IOS Press, 2021)
    Texto en actas de congreso
    Acceso abierto
    In this paper we analyze the effect of selecting the root in a tree decomposition when using decomposition-based backtracking algorithms. We focus on optimization tasks for Graphical Models using the BTD algorithm. We show ...
  • Employee scheduling with SAT-based pseudo-boolean constraint solving 

    Nieuwenhuis, Robert Lukas Mario; Oliveras Llunell, Albert; Rodríguez Carbonell, Enric; Rollón Rico, Emma (Institute of Electrical and Electronics Engineers (IEEE), 2021)
    Artículo
    Acceso abierto
    The aim of this paper is practical: to show that, for at least one important real-world problem, modern SAT-based technology can beat the extremely mature branch-and-cut solving methods implemented in well-known state-of-the-art ...
  • A heuristic approach to the design of optimal cross-docking boxes 

    Nieuwenhuis, Robert Lukas Mario; Oliveras Llunell, Albert; Rodríguez Carbonell, Enric (Institute of Electrical and Electronics Engineers (IEEE), 2021-09-03)
    Artículo
    Acceso abierto
    Multinational companies frequently work with manufacturers that receive large orders for different products (or product varieties: size, shape, color, texture, material), to serve thousands of different final destinations ...
  • Stuck-at-off fault analysis in memristor-based architecture for synchronization 

    Escudero, Manuel; Vourkas, Ioannis; Rubio Gimeno, Alberto (Institute of Electrical and Electronics Engineers (IEEE), 2019)
    Texto en actas de congreso
    Acceso restringido por política de la editorial
    Nonlinear circuits may be interconnected and organized in networks to couple their dynamics and achieve synchronization, a process that is commonly observed in nature. Recent works have shown that memristors may be used ...
  • Decision levels are stable: towards better SAT heuristics 

    Nieuwenhuis, Robert Lukas Mario; Lozano Navarro, Adrián; Oliveras Llunell, Albert; Rodríguez Carbonell, Enric (EasyChair Publications, 2020)
    Texto en actas de congreso
    Acceso restringido por política de la editorial
    We shed new light on the Literal Block Distance (LBD) and glue-based heuristics used in current SAT solvers. For this, we first introduce the concept of stickiness: given a run of a CDCL SAT solver, for each pair of literals ...
  • First-order completion with ordering constraints: some positive and some negative results 

    Nieuwenhuis, Robert Lukas Mario; Rubio Gimeno, Alberto (1991-10-15)
    Report de recerca
    Acceso abierto
    We show by means of counter examples that some well-known results on the completeness of deduction methods with ordering constraints are incorrect. The problem is caused by the fact that the usual lifting lemmata do not ...
  • Basic superposition is complete 

    Nieuwenhuis, Robert Lukas Mario; Rubio Gimeno, Alberto (1991-10-15)
    Report de recerca
    Acceso abierto
    We define a formalism of equality constraints and use it to prove the completeness of what we have called basic superposition: a restricted form of superposition in which only the subterms not originated in previous ...
  • Augmenting the power of (partial) MaxSat resolution with extension 

    Larrosa Bondia, Francisco Javier; Rollón Rico, Emma (AAAI Press, 2020)
    Comunicación de congreso
    Acceso restringido por política de la editorial
    The refutation power of SAT and MaxSAT resolution is challenged by problems like the soft and hard Pigeon Hole Problem PHP for which short refutations do not exist. In this paper we augment the MaxSAT resolution proof ...
  • On one query self-reducible sets 

    Lozano Bojados, Antoni; Ogiwara, Mitsunori (1991-01)
    Report de recerca
    Acceso abierto
    We study one word-decreasing self-reducible sets, which were introduced by Lozano and Torán. These are usual self-reducible sets with the peculiarity that the self-reducibility machine makes at most one query and this is ...
  • Proving termination through conditional termination 

    Borralleras Andreu, Cristina; Brockschmidt, Marc; Larraz Hurtado, Daniel; Oliveras Llunell, Albert; Rodríguez Carbonell, Enric; Rubio Gimeno, Alberto (Springer, 2017)
    Texto en actas de congreso
    Acceso abierto
    We present a constraint-based method for proving conditional termination of integer programs. Building on this, we construct a framework to prove (unconditional) program termination using a powerful mechanism to combine ...
  • Incomplete SMT techniques for solving non-linear formulas over the integers 

    Borralleras Andreu, Cristina; Larraz Hurtado, Daniel; Rodríguez Carbonell, Enric; Oliveras Llunell, Albert; Rubio Gimeno, Alberto (2019-08-01)
    Artículo
    Acceso abierto
    We present new methods for solving the Satisfiability Modulo Theories problem over the theory of QuantifierFree Non-linear Integer Arithmetic, SMT(QF-NIA), which consists of deciding the satisfiability of ground formulas ...
  • Short proofs of the Kneser-Lovász coloring principle 

    Aisenberg, James; Bonet Carbonell, M. Luisa; Buss, Sam; Craciun, Adrian; Istrate, Gabriel (2018-08)
    Artículo
    Acceso abierto
    We prove that propositional translations of the Kneser–Lovász theorem have polynomial size extended Frege proofs and quasi-polynomial size Frege proofs for all fixed values of k. We present a new counting-based combinatorial ...

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