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Between a Rock and a Hard Place: Parsing for Hyperege Replacement DAG Grammars
Umeå University, Faculty of Science and Technology, Department of Computing Science. (Foundations of Language Processing)
Umeå University, Faculty of Science and Technology, Department of Computing Science. (Foundations of Language Processing)ORCID iD: 0000-0001-7349-7693
Umeå University, Faculty of Science and Technology, Department of Computing Science. (Foundations of Language Processing)
2016 (English)In: Proc. 10th International Conference on Language and Automata Theory and Applications (LATA 2016) / [ed] A.H. Dediu, J. Janoušek, C. Martín-Vide, and B. Truthe, Springer Publishing Company, 2016, Vol. 9618, p. 521-532Conference paper, Published paper (Refereed)
Abstract [en]

Motivated by applications in natural language processing, we study the uniform membership problem for hyperedge-replacement grammars that generate directed acyclic graphs. Our major result is a low-degree polynomial-time algorithm that solves the uniform membership problem for a restricted type of such grammars. We motivate the necessity of the restrictions by two different NP-completeness results.

Place, publisher, year, edition, pages
Springer Publishing Company, 2016. Vol. 9618, p. 521-532
Series
Lecture Notes in Computer Science, ISSN 0302-9743 ; 9618
Keywords [en]
Graph grammar, Hyperedge replacement, Abstract meaning representation, DAG grammar, Uniform membership problem, Parsing
National Category
Computer Sciences
Identifiers
URN: urn:nbn:se:umu:diva-111984DOI: 10.1007/978-3-319-30000-9_40ISI: 000378745100045ISBN: 978-3-319-30000-9 (print)ISBN: 978-3-319-29999-0 (print)OAI: oai:DiVA.org:umu-111984DiVA, id: diva2:874860
Conference
10th International Conference on Language and Automata Theory and Applications (LATA 2016), Prague, Czech Republic, March 14-18, 2016
Available from: 2015-11-29 Created: 2015-11-29 Last updated: 2019-01-07Bibliographically approved
In thesis
1. Complexity and expressiveness for formal structures in Natural Language Processing
Open this publication in new window or tab >>Complexity and expressiveness for formal structures in Natural Language Processing
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The formalized and algorithmic study of human language within the field of Natural Language Processing (NLP) has motivated much theoretical work in the related field of formal languages, in particular the subfields of grammar and automata theory. Motivated and informed by NLP, the papers in this thesis explore the connections between expressibility – that is, the ability for a formal system to define complex sets of objects – and algorithmic complexity – that is, the varying amount of effort required to analyse and utilise such systems. Our research studies formal systems working not just on strings, but on more complex structures such as trees and graphs, in particular syntax trees and semantic graphs. The field of mildly context-sensitive languages concerns attempts to find a useful class of formal languages between the context-free and context-sensitive. We study formalisms defining two candidates for this class; tree-adjoining languages and the languages defined by linear context-free rewriting systems. For the former, we specifically investigate the tree languages, and define a subclass and tree automaton with linear parsing complexity. For the latter, we use the framework of parameterized complexity theory to investigate more deeply the related parsing problems, as well as the connections between various formalisms defining the class. The field of semantic modelling aims towards formally and accurately modelling not only the syntax of natural language statements, but also the meaning. In particular, recent work in semantic graphs motivates our study of graph grammars and graph parsing. To the best of our knowledge, the formalism presented in Paper III of this thesis is the first graph grammar where the uniform parsing problem has polynomial parsing complexity, even for input graphs of unbounded node degree.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2017. p. 18
Series
Report / UMINF, ISSN 0348-0542 ; 17.13
Keywords
graph grammars, formal languages, natural language processing, parameterized complexity, abstract meaning representation, tree automata, deterministic tree-walking transducers, mildly context-sensitive languages, hyperedge replacement, tree adjoining languages, minimally adequate teacher
National Category
Computer Sciences
Identifiers
urn:nbn:se:umu:diva-135014 (URN)9789176017227 (ISBN)
Presentation
2017-05-19, MA121, MIT-huset 901 87 Umeå, Umeå, 10:15 (English)
Supervisors
Available from: 2017-05-17 Created: 2017-05-16 Last updated: 2018-06-09Bibliographically approved
2. Order-preserving graph grammars
Open this publication in new window or tab >>Order-preserving graph grammars
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Ordningsbevarande grafgrammatiker
Abstract [en]

The field of semantic modelling concerns formal models for semantics, that is, formal structures for the computational and algorithmic processing of meaning. This thesis concerns formal graph languages motivated by this field. In particular, we investigate two formalisms: Order-Preserving DAG Grammars (OPDG) and Order-Preserving Hyperedge Replacement Grammars (OPHG), where OPHG generalise OPDG.

Graph parsing is the practise of, given a graph grammar and a graph, to determine if, and in which way, the grammar could have generated the graph. If the grammar is considered fixed, it is the non-uniform graph parsing problem, while if the grammars is considered part of the input, it is named the uniform graph parsing problem. Most graph grammars have parsing problems known to be NP-complete, or even exponential, even in the non-uniform case. We show both OPDG and OPHG to have polynomial uniform parsing problems, under certain assumptions.

We also show these parsing algorithms to be suitable, not just for determining membership in graph languages, but for computing weights of graphs in graph series.

Additionally, OPDG is shown to have several properties common to regular languages, such as MSO definability and MAT learnability. We moreover show a direct corresponcence between OPDG and the regular tree grammars.

Finally, we present some limited practical experiments showing that real-world semantic graphs appear to mostly conform to the requirements set by OPDG, after minimal, reversible processing.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, Institutionen för datavetenskap, 2019. p. 56
Series
Report / UMINF, ISSN 0348-0542 ; 19.01
Keywords
Graph grammars, graph parsing, graph series, hyperedge replacement, uniform parsing problem, abstract meaning representation, semantic modelling, order preservation, reentrancy preservation, minimally adequate teacher, weighted graph grammars
National Category
Computer Sciences
Identifiers
urn:nbn:se:umu:diva-154777 (URN)978-91-7855-017-3 (ISBN)
Public defence
2019-02-04, MA121, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2019-01-14 Created: 2019-01-07 Last updated: 2019-07-05Bibliographically approved

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Björklund, HenrikDrewes, FrankEricson, Petter

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