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4 - Unification grammars

Published online by Cambridge University Press:  25 October 2011

Nissim Francez
Affiliation:
Technion - Israel Institute of Technology, Haifa
Shuly Wintner
Affiliation:
University of Haifa, Israel
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Summary

Feature structures are the building blocks of unification grammars, as they serve as the counterpart of the terminal and nonterminal symbols in CFGs. However, in order to define grammars and derivations, one needs some extension of feature structures to sequences thereof. In this chapter we present multirooted feature structures that are aimed at capturing complex, ordered information and are used for representing rules and sentential forms of unification grammars; we motivate this extension in Section 4.1. In parallel to the exposition of feature structures in Chapter 2, we start by defining multirooted feature graphs (Section 4.2), a natural extension of feature graphs. We then abstract away from the identities of nodes in the graphs in two ways: by defining multirooted feature structures, which are equivalence classes of isomorphic multirooted feature graphs, and by defining abstract multirooted structures (Section 4.3). Finally, we define the concept of multi-AVMs (Section 4.4), which are an extension of AVMs, and show how they correspond to multirooted graphs. The crucial concept of unification in context is discussed in Section 4.5.

We then utilize this machinery for defining unification grammars. We begin by defining (sentential) forms and grammar rules (Section 4.6). Then, we define the concept of derivation for unification grammars, providing a means for defining the languages generated by such grammars (Section 4.7). We explore derivation trees in Section 4.8.

The move from context-free grammars to unification grammars is motivated by linguistic considerations (the need to provide better generalizations and more compact representations).

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Unification Grammars , pp. 115 - 164
Publisher: Cambridge University Press
Print publication year: 2011

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  • Unification grammars
  • Nissim Francez, Technion - Israel Institute of Technology, Haifa, Shuly Wintner, University of Haifa, Israel
  • Book: Unification Grammars
  • Online publication: 25 October 2011
  • Chapter DOI: https://doi.org/10.1017/CBO9781139013574.005
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  • Unification grammars
  • Nissim Francez, Technion - Israel Institute of Technology, Haifa, Shuly Wintner, University of Haifa, Israel
  • Book: Unification Grammars
  • Online publication: 25 October 2011
  • Chapter DOI: https://doi.org/10.1017/CBO9781139013574.005
Available formats
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Save book to Google Drive

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.

  • Unification grammars
  • Nissim Francez, Technion - Israel Institute of Technology, Haifa, Shuly Wintner, University of Haifa, Israel
  • Book: Unification Grammars
  • Online publication: 25 October 2011
  • Chapter DOI: https://doi.org/10.1017/CBO9781139013574.005
Available formats
×