Minimalist Parsing

1. Minimalist Parsing Scott Drellishak CompLing Lab Meeting 2/1/2006

2. Overview • Four parts: • Whirlwind tour of Minimalism • Formal definition of a Minimalist Grammar • Algorithms for parsing MGs • Software and web sites

3. Four parts: • Whirlwind tour of Minimalism • Formal definition of a Minimalist Grammar • Algorithms for parsing MGs • Software and web sites

4. 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)

5. Minimalism • Sentence derivations proceed according to this (famous) diagram: Lexicon Phonetic Form (PF) Logical Form (LF)

6. 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.

7. 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.)

8. Four parts: • Whirlwind tour of Minimalism • Formal definition of a Minimalist Grammar • Algorithms for parsing MGs • Software and web sites

9. 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.)

10. 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)

11. 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”

12. 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?

13. 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

14. 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)

15. 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/

16. A Sample Derivation • Let’s take a look at the derivation of a simple sentence from Stabler (1997)…

17. Four parts: • Whirlwind tour of Minimalism • Formal definition of a Minimalist Grammar • Algorithms for parsing MGs • Software and web sites

18. 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.

19. MG Operations

20. 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.

21. 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)

22. 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)

23. Four parts: • Whirlwind tour of Minimalism • Formal definition of a Minimalist Grammar • Algorithms for parsing MGs • Software and web sites

24. 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.

25. 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.