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  • 1.
    Bensch, Suna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Drewes, Frank
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Jürgensen, Helmut
    Department of Computer Science, Western University, London, Canada.
    van der Merwe, Brink
    Department of Computer Science, Stellenbosch University, South Africa.
    Graph transformation for incremental natural language analysis2014Ingår i: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 531, s. 1-25Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Millstream systems have been proposed as a non-hierarchical method for modelling natural language. Millstream configurations represent and connect multiple structural aspects of sentences. We present a method by which the Millstream configurations corresponding to a sentence are constructed. The construction is incremental, that is, it proceeds as the sentence is being read and is complete when the end of the sentence is reached. It is based on graph transformations and a lexicon which associates words with graph transformation rules that implement the incremental construction process.

  • 2.
    Berglund, Martin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Björklund, Henrik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Björklund, Johanna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Shuffled languages: representation and recognition2013Ingår i: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 489-490, s. 1-20Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Language models that use interleaving, or shuffle, operators have applications in various areas of computer science, including system verification, plan recognition, and natural language processing. We study the complexity of the membership problem for such models, in other words, how difficult it is to determine if a string belongs to a language or not. In particular, we investigate how interleaving can be introduced into models that capture the context-free languages.

  • 3.
    Berglund, Martin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    van der Merwe, Brink
    On the semantics of regular expression parsing in the wild2017Ingår i: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 679, s. 69-82Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We introduce prioritized transducers to formalize capturing groups in regular expression matching in a way that permits straightforward modeling of capturing in Java's 1 regular expression library. The broader questions of parsing semantics and performance are also considered. In addition, the complexity of deciding equivalence of regular expressions with capturing groups is investigated.

  • 4.
    Björklund, Henrik
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Björklund, Johanna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Zechner, Niklas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Compression of finite-state automata through failure transitions2014Ingår i: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 557, s. 87-100Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Several linear-time algorithms for automata-based pattern matching rely on failure transitions for efficient back-tracking. Like epsilon transitions, failure transition do not consume input symbols, but unlike them, they may only be taken when no other transition is applicable. At a semantic level, this conveniently models catch-all clauses and allows for compact language representation.

    This work investigates the transition-reduction problem for deterministic finite-state automata (DFA). The input is a DFA A and an integer k. The question is whether k or more transitions can be saved by replacing regular transitions with failure transitions. We show that while the problem is NP-complete, there are approximation techniques and heuristics that mitigate the computational complexity. We conclude by demonstrating the computational difficulty of two related minimisation problems, thereby cancelling the ongoing search for efficient algorithms.

  • 5.
    Björklund, Henrik
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Schwentick, Thomas
    On notions of regularity for data languages2010Ingår i: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 411, nr 4-5, s. 702-715Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    With motivation from considerations in XML database theory and model checking, data strings have been introduced as an extension of finite alphabet strings which carry, at each position, a symbol and a data value from an infinite domain. Previous work has shown that it is difficult to come up with an expressive yet decidable automaton model for data languages. Recently, such a model, data automata, was introduced. This paper introduces a simpler but equivalent model and investigates its expressive power, algorithmic and closure properties, and some extensions.

  • 6.
    Björklund, Johanna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Drewes, Frank
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Jonsson, Anna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Finding the N Best Vertices in an Infinite Weighted Hypergraph2017Ingår i: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 682, s. 78s. 30-41Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose an algorithm for computing the N best vertices in a weighted acyclic hypergraph over a nice semiring. A semiring is nice if it is finitely-generated, idempotent, and has 1 as its minimal element. We then apply the algorithm to the problem of computing the N best trees with respect to a weighted tree automaton, and complement theoretical correctness and complexity arguments with experimental data. The algorithm has several practical applications in natural language processing, for example, to derive the N most likely parse trees with respect to a probabilistic context-free grammar. 

  • 7.
    Björklund, Johanna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Öhman, Lars-Daniel
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Simulation relations for pattern matching in directed graphs2013Ingår i: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 485, s. 1-15Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider the problem of finding the occurrences of a pattern tree t in a directed graph g, and propose two algorithms, one for preprocessing and one for searching for t in g. It is assumed that the object graph itself is large and static, and that the pattern tree is small and frequently updated. To model varying abstraction levels in the data, we work with partially ordered alphabets and compute simulation relations rather than equivalence relations. In particular, vertices and edges are labelled with elements from a pair of preorders instead of unstructured alphabets. Under the above assumptions, we obtain a search algorithm that runs in time O(height (t) . vertical bar t vertical bar . vertical bar(V-g(+/-)t/R-g(+/-)t vertical bar(2)) where vertical bar (V-g(+/-)t/R-g(+/-)t)vertical bar is the number of equivalence classes in the coarsest simulation relation R-g(+/-)t on the graph g((+/-))t, the disjoint union of g and t. This means that the size of the object graph only affects the running time of the search algorithm indirectly, because of the groundwork done by the preprocessing routine in time O(k . vertical bar g vertical bar . vertical bar(V-g/R-g)vertical bar(2)), where vertical bar(V-g/R-g) is the number of equivalence classes in the coarsest simulation relation R-g on g, taking k = vertical bar V-g vertical bar(2) in the general case and k = height (g) if g is acyclic.

  • 8.
    Drewes, Frank
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Preface2017Ingår i: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 679, s. 1-1Artikel i tidskrift (Övrigt vetenskapligt)
  • 9.
    Drewes, Frank
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Janssens, Dirk
    University of Antwerp.
    Hoffmann, Berthold
    University of Bremen.
    Minas, Mark
    University of the German Armed Forces Munich.
    Adaptive Star grammars and their languages2010Ingår i: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 411, nr 34-36, s. 3090-3109Artikel i tidskrift (Refereegranskat)
  • 10.
    Jäger, Gerold
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Drewes, Frank
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    The Metric Dimension of Z(n) x Z(n) x Z(n) is [3n/2]2020Ingår i: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 806, s. 78s. 344-362Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work we determine the metric dimension of Zn × Zn × Zn as ⌊3n/2⌋ for all n ≥ 2. We prove this result by investigating a variant of Mastermind.

    Mastermind is a famous two-player game that has attracted much attention in the literature in recent years. In particular we consider the static (also called non-adaptive) black-peg variant of Mastermind. The game is played by a codemaker and a codebreaker. Given c colors and p pegs, the principal rule is that the codemaker has to choose a secret by assigning colors to the pegs, i.e., the secret is a p-tuple of colors, and the codebreaker asks a number of questions all at once. Like the secret, a question is a p-tuple of colors chosen from the c available colors. The codemaker then answers all of those questions by telling the codebreaker how many pegs in each question are correctly colored. The goal is to find the minimal number of questions that allows the codebreaker to determine the secret from the received answers. We present such a strategy for this game for p = 3 pegs and an arbitrary number c ≥ 2 of colors using ⌊3c/2⌋ + 1 questions, which we prove to be both feasible and optimal.

    The minimal number of questions required for p pegs and c colors is easily seen to be equal to the metric dimension of Zcp plus 1 which proves our main result.

  • 11.
    Jäger, Gerold
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Peczarski, Marcin
    Bounding memory for Mastermind might not make it harder2015Ingår i: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 596, s. 55-66Artikel i tidskrift (Refereegranskat)
1 - 11 av 11
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  • en-US
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