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  • 1.
    Bevemyr, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Computing Science Department.
    Data-parallel Implementation of Prolog1996Doctoral thesis, comprehensive summary (Other academic)
  • 2.
    Dell'Acqua, Pierangelo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Computing Science Department.
    Reflection Principles in Computational Logic1998Doctoral thesis, monograph (Other academic)
    Abstract [en]

    We introduce the concept of reflection principles as a knowledge representation paradigm in a computational logic setting. Reflection principles are expressed as certain kinds of logic schemata intended to capture the basic properties of the domain knowledge to be modelled. Reflection is then used to instantiate these schemata to answer specific queries about the domain.

    This differs from other approaches to reflection mainly in the following three ways. First, it uses logical instead of procedural reflection. Second, it aims at a cognitively adequate declarative representation of various forms of knowledge and reasoning, as opposed to reflection as a means for controlling computation or deduction. Third, it facilitates the building of a complex theory by allowing a simpler theory to be enhanced by a compact metatheory, contrary to the construction of metatheories that are only conservative extensions of the basic theory.

    A computational logic system for embedding reflection principles, called RCL (for Reflective Computational Logic), is presented in full detail. The system is an extension of Horn clause resolution-based logic, and is devised in a way that makes important features of reflection parametric as much as possible, so that they can be tailored according to specific needs of different application domains. Declarative and procedural semantics of the logic are described and correctness and completeness of reflection as logical inference are proved. Examples of reflection principles for three different application areas are shown.

    The proposed approach to reflection is powerful and flexible enough to be integrated into different frameworks. We show how the use of reflection principles can be integrated into a framework of rational, reactive agents to enhance their reasoning capabilities. Finally, relationship with a variety of distinct sources within the literature on relevant topics is discussed.

  • 3.
    Hjerpe, Torkel
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Computing Science Department.
    High-level specification and efficient solving of constraint satisfaction problems1995Doctoral thesis, comprehensive summary (Other academic)
  • 4.
    Lindgren, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Computing Science Department.
    Compilation Techniques for Prolog1996Doctoral thesis, comprehensive summary (Other academic)
  • 5.
    Mildner, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Computing Science Department.
    Type Domains for Abstract Interpretation: A critical study1999Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Programming languages with dynamic typing such as Prolog do not require that the programmer declares the types of data or procedures. This flexibility, however, comes at a price. The lack of declarations makes it hard for a compiler to produce fast code since data must be assumed to be of any type.

    Abstract interpretation is a technique to automatically infer conservative approximations of program properties such as the types of program variables and procedure arguments. The properties of interest are described using an abstract domain. The abstract domains for type analysis investigated in this thesis are based on deterministic term grammars but differ in the representation of the term grammars and in the widening used, that is, the method used to ensure that the analysis terminates.

    One proposed representation of term grammars, type graphs, are shown to be exponentially larger than the term grammars they represent not only in the worst case but also in practice. One previously proposed widening for type graphs is shown to be impractically expensive and also no more precise than other more efficient methods. A novel implementation technique is proposed for another type graph widening that appears in the literature. The precision using this implementation technique is shown to be better than for the other investigated widenings. The performance, however, suffers from the problems inherent in the type graph representation unless some crucial modifications to the analyzer are made.

    To overcome the problems with the type graph representation a more compact representation of term grammars is proposed. A number of widenings using this representation are investigated and shown not to suffer from problems with huge term grammar representations. The precision obtained using these widenings are as good or better than the precision obtained using the original widening proposed for type graphs.

    Finally, two sets of benchmarks that have been used in the literature to investigate analysis methods are considered. It is shown that these benchmarks will give unrealistically good absolute precision and one set of benchmarks, the GAIA benchmarks, is shown to have further deficiencies that make it completely unsuitable for benchmarking purposes.

  • 6.
    Montelius, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Computing Science Department. Swedish Institute of Computer Science.
    Exploiting Fine-grain Parallelism in Concurrent Constraint Languages1997Doctoral thesis, monograph (Other academic)
  • 7.
    Nyström, Sven-Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Computing Science Department.
    Denotational Semantics for Asynchronous Concurrent Languages1996Doctoral thesis, monograph (Other academic)
  • 8.
    Ottosson, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computing Science. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computing Science.
    Integration of Constraint Programming and Integer Programming for Combinatorial Optimization2000Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The last several years have seen an increasing interest in combining the models and methods of optimization with those of constraint programming. Integration of the two was initially impeded by their different cultural origins, one having developed largely in the operations research community and the other in the computer science and artificial intelligence communities. The advantages of merger, however, are rapidly overcomingthis barrier.

    The main objective for an integration of Constraint Programming over finite domains (CP) and Integer Programming (IP) is to take advantage of both the inference through constraint propagation and the (continuous) relaxations through Linear Programming (LP), in order to reduce the search needed to find feasible, good and optimal solutions.

    The key decisions to be made for integrating CP and IP are (a) the model(s), (b) the inference, (c) the relaxations, and, (d) the search and branching strategies to use. In this thesis it is advocated to model specifically for a hybrid solver, having part of the model operated on by CP inference and part of the model constituting an LP relaxation. We propose mixed (global) constraints spanning both discrete and continuous variables to bridge the gap between CP and LP, providing inference as well as information for search strategies. Inference comes as cutting planes and domains reductions for LPand CP respectively. Branching is done in the CP part, utilizing information from the LP relaxation.

    Apart from a general framework for integration, specific constraints and structures studied include several variations of variable subscripts and piecewise linear functions. Computational experiments show the benefit and potential of a hybrid scheme, illustrated on production planning and configuration problems.

  • 9.
    Thalmann, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computing Science. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computing Science.
    Term-modal logic and quantifier-free dynamic assignment logic2000Doctoral thesis, monograph (Other academic)
    Abstract [en]

    In this dissertation, we present two new sorts of computer sciencelogics.

    Many powerful logics exist today for reasoning about multi-agentsystems, but in most of these it is hard to reason about an infiniteor indeterminate number of agents. Also the naming schemes used inthe logics often lack expressiveness to name agents in an intuitiveway.

    To obtain a more expressive language for multi-agent reasoning and abetter naming scheme for agents, we introduce in the first part of thedissertation a family of logics called term-modal logics. A mainfeature of our logics is the use of modal operators indexed by theterms of the logics. Thus, one can quantify over variables occurringin modal operators. In term-modal logics agents can be represented byterms, and knowledge of agents is expressed with formulas within thescope of modal operators.

    This gives us a flexible and uniform language for reasoning about theagents themselves and their knowledge. We give examples of theexpressiveness of the languages and provide sequent-style andtableau-based proof systems for the logics. Furthermore, we giveproofs of soundness and completeness with respect to the possibleworld semantics.

    In the second part of the dissertation, we treat another problem inreasoning about multi-agent systems, namely the problem of informationupdating. We develop a dynamic logic of assignments with a scopingoperator instead of quantifiers. Function, relation symbols and logicvariables are all rigidly interpreted in our semantics, while programvariables are non-rigid. The scoping operator is used to distinguishbetween the value of a program variable before and after the executionof a program.

    We provide a tableau proof system for the logic. First, the system isproved complete without the star operator, and then with the staroperator using an omega rule. The full logic is shown to beundecidable, while some interesting fragments are decidable.

  • 10.
    Veanes, Margus
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Computing Science Department.
    On Simultaneous Rigid E-Unification1997Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Automated theorem proving methods in classical logic with equality that are based on the Herbrand theorem, reduce to a problem called Simultaneous Rigid E-Unification, or SREU for short. Recent developments show that SREU has also close connections with intuitionistic logic with equality, second-order unification, some combinatorial problems and finite tree automata.

    We show new decidability results of various cases of SREU. In particular, we improve upon the undecidability result of SREU by showing its undecidability in a very restricted case, in fact the minimal known case. We prove the decidability of some cases of SREU under certain restrictions regarding the number of variables and other syntactical criteria. To prove the (computational) complexity of some cases, we reduce them to certain decision problems of finite tree automata. The complexity of the latter problems is studied first. In connection with that, we present a survey of closely related problems and give a comparison with the corresponding results in classical automata theory.

    These results are applied in the context of intuitionistic logic with equality, to obtain a complete classification of its prenex fragment in terms of the quantifier prefix: the ∃∃-fragment is shown undecidable and the ∀*∃∀*-fragment is shown decidable. These results have further implications for proof search in intuitionistic logic with equality.

    We also improve upon a number of other recent undecidability results that are related to the so-called Herbrand Skeleton problem and are of fundamental importance in automated theorem proving in in classical logic with equality. In that context we also prove, as our main tool, a logical theorem that we believe is of independent interest.

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