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Minimalist Parsing. Scott Drellishak CompLing Lab Meeting 2/1/2006. Overview. Four parts: Whirlwind tour of Minimalism Formal definition of a Minimalist Grammar Algorithms for parsing MGs Software and web sites. Four parts: Whirlwind tour of Minimalism

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Minimalist parsing
Minimalist Parsing

Scott Drellishak

CompLing Lab Meeting

2/1/2006


Overview
Overview

  • Four parts:

    • Whirlwind tour of Minimalism

    • Formal definition of a Minimalist Grammar

    • Algorithms for parsing MGs

    • Software and web sites


  • Four parts:

    • Whirlwind tour of Minimalism

    • Formal definition of a Minimalist Grammar

    • Algorithms for parsing MGs

    • Software and web sites


Minimalism
Minimalism

  • Minimalism

    • Recent version of transformational generative grammar. Chomsky’s (1995) The Minimalist Program.

    • Updates and supersedes earlier GB/P&P

    • Explores “the extent to which previous empirical coverage can be maintained with fewer grammatical devices.” (Stabler 1999: 299)


Minimalism1
Minimalism

  • Sentence derivations proceed according to this (famous) diagram:

Lexicon

Phonetic Form (PF)

Logical Form (LF)


Minimalism2
Minimalism

  • Items come out of the lexicon fully inflected and with features: interpretable and uninterpretable.

  • Uninterpretable features must cancel out before the derivation reaches LF.

  • The branch to PF allows the surface form to “peek” into the middle of the derivation.

  • Cross-linguistic differences are accounted for by variations in the lexicon.


Minimalism3
Minimalism

  • Trees are derived by starting with singleton trees (lexical items) and combining them.

  • Only two operations:

    • On two trees: merge them together into a single tree (with one “projecting over” the other).

    • On a single tree: move a node in the tree up to the root to cancel a feature.

  • (We’ll see a couple of derivations later.)


  • Four parts:

    • Whirlwind tour of Minimalism

    • Formal definition of a Minimalist Grammar

    • Algorithms for parsing MGs

    • Software and web sites


Minimalist grammars
Minimalist Grammars

  • For parsing, Minimalism needs formalization.

  • Stabler (1997) defines a MG as:

    V = phonetic and interpretable features

    Cat = categories, selectors, licensors, licensees

    Lex = expressions (trees) built from V and Cat

    F = { merge, move }

  • (Based on an earlier grammar formalism, so the names don’t mean what you think.)


V lexicon
V = Lexicon

  • Lexical entries like:

    =n d –case every (category D, selects a N, needs case) n language (category N)

    =d +case =d v speaks (category V, 2 DPs, assigns case to 1)

  • This is a DP analysis

  • “speaks” stands for /speaks/(speaks)


Cat features
Cat = Features

  • Base: c, t, v, d, n, … (parts of speech)

  • Select: =x, =X, X= (selects arguments)

    • Select features trigger merge

    • Upper-case moves phonetic content to merged node; “=” determines prefix or postfix

  • Licensees: -case, -wh, … (needs…)

  • Licensors: +case, +wh, … (provides…)

    • L* features trigger move; upper-case = “strong”


Lex trees
Lex = Trees

  • A set of nodes and three relations:

  • Dominance (x⊳y = x is y’s parent)

    • Who’s higher in the tree?

  • Precedence (x≺y = x precedes y)

    • Who’s before who in the tree?

  • Projection (x < y = x projects over y)

    • Whose features percolate up to the parent?


F operations
F = Operations

  • merge: Combines two trees. A head selects and combines with a phrase to its right:

    =d =d v make + d lunch ⇒

    <=d v make lunch


F operations1
F = Operations

  • If the selector feature is upper case, only the phonetic features combine:

    D= =d v make + d lunch ⇒

    <=d v /lunch make/(make) (lunch)


F operations2
F = Operations

  • move: One tree’s head’s +x feature attracts the nearest –x feature to the root of the tree:

    <+case v speak -case Nahuatl

    >(Nahuatl) < v speak /Nahuatl/


A sample derivation
A Sample Derivation

  • Let’s take a look at the derivation of a simple sentence from Stabler (1997)…


  • Four parts:

    • Whirlwind tour of Minimalism

    • Formal definition of a Minimalist Grammar

    • Algorithms for parsing MGs

    • Software and web sites


Parsing mgs
Parsing MGs

  • Stabler (2000 and 2001) describes a CYK-like algorithm for parsing MGs.

  • Defines a set of operations on strings of features that are arranged in “chains” (forests of incomplete trees).

  • Each of these operations operates on a contiguous range of the forest, so they can be chart-parsed to recognize input sentences.



CYK?

  • Somewhat different from the version of CYK used to parse CFGs, but it’s still the same idea.

  • Each operation transforms a string of features, canceling out selection and licensing features, producing more strings, which are stored in the chart.

  • Then, look for further operations that take them as input, building a hierarchy.


Another recognizer
Another Recognizer

  • Stabler refers to Harkema (2000), which defines a MG recognizer that works more like an Earley parser.

  • It has an agenda and a chart. As operations are applied to make new items, those go into the agenda. Stop when a “goal item” appears in the chart.

  • Overall time complexity is O(n4k+4)


Another sample derivation
Another Sample Derivation

  • Here’s a derivation from Stabler (2000)—a slightly different format; note indices:

    1. (0,1)::=d v –w lexical

    2. (1,2)::d –case lexical

    3. (x,x)::=v +case acc lexical

    4. (x,x)::=acc +w w lexical

    5. (0,1):v -w,(1,2):-case merge3(1,2)

    6. (x,x):+case acc,(0,1):-w,(1,2):-case merge3(3,5)

    7. (1,2):acc,(0,1):-w move1(6)

    8. (1,2):+w w,(0,1):-w merge1(4,7)

    9. (0,2):w move1(8)


  • Four parts:

    • Whirlwind tour of Minimalism

    • Formal definition of a Minimalist Grammar

    • Algorithms for parsing MGs

    • Software and web sites


Parsers
Parsers

  • Stabler’s parsers: MG parsers in Ocaml and two flavors of Prolog. (Also requires tcl/tk.)

  • Sourabh Niyogi: Stabler-based MG parser in Scheme, does verb subcategorization.

  • Willemijn Vermaat: Stabler-based MG parser w/ web interface (that I couldn’t figure out).

  • Dekang Lin: MINIPAR. Executable only, based on PRINCIPAR, not clear what the internals are like.


References
References

Chomsky (1995). The Minimalist Program.

Harkema (2000). A Recognizer for Minimalist Grammars.

Stabler (1997). Derivational Minimalism.

Stabler (1999). Remnant Movement and Structural Complexity.

Stabler (2000). Minimalist Grammars and Recognition.


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