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LING 388: Language and Computers

LING 388: Language and Computers. Sandiway Fong 9/ 17 Lecture 7. Last Time. Prolog term notation: functor (argument 1 ,..,argument n ) functor must be a symbol arguments can be simple terms or (recursive) complex terms We will use Prolog terms to represent parse trees: Example:

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LING 388: Language and Computers

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  1. LING 388: Language and Computers Sandiway Fong 9/17 Lecture 7

  2. Last Time • Prolog term notation: • functor(argument1,..,argumentn) • functor must be a symbol • arguments can be simple terms or (recursive) complex terms • We will use Prolog terms to represent parse trees: • Example: s(np(prp(i),vp(vbd(saw),np(dt(the),nn(boy)),pp(in(with),np(dt(a),nn(telescope)))))

  3. Last Time Homework 2

  4. Administrivia • Homework 2 is designed to test your understanding of the Prolog term data structure • due Thursday night!

  5. Computing Parse Trees • Getting Prolog to build a representation of the parse tree [S [NP [Det the] man][VP [V took][NP [Det the] book]]] sentence(np(det(the),man),vp(verb(took),np(det(the),book)))

  6. observation ?- trace. we can step through the derivation but it disappears after computation is finished would be nice to keep a parse tree around Programming technique add one argument (parameter) to each non-terminal of each grammar rule to hold the part of the parse tree it computes Rule of compositionality: rules combine sub-phrases into larger phrases We will combine sub-trees to form larger trees eventually resulting in the complete parse tree Computing Parse Trees

  7. Computing Parse Trees • use a recursive Prolog data structure to represent a parse • examples • data structure:verb(took) • functor = verb • argument = took • data structure:det(the) • functor = det • argument = the • data structure:np(det(the),man) • functor = np • 1st argument = det(the) • functor = det • argument = the • 2nd argument = man (1) verb | took (2) det | the (3) np / \ det man | the

  8. Computing Parse Trees • original DCG • sentence --> np, vp. • vp --> verb, np. • verb --> [took]. • np --> det, [man]. • np --> det, [book]. • det --> [the]. • revised DCG • sentence(s(NP,VP)) --> np(NP), vp(VP). • vp(vp(V,NP)) --> verb(V), np(NP). • verb(v(took)) --> [took]. • np(np(D,man)) --> det(D), [man]. • np(np(D,book)) --> det(D), [book]. • det(det(the)) --> [the].

  9. Computing Parse Trees • revised DCG • sentence(s(NP,VP)) --> np(NP), vp(VP). • vp(vp(V,NP)) --> verb(V), np(NP). • verb(v(took)) --> [took]. • np(np(D,man)) --> det(D), [man]. • np(np(D,book)) --> det(D), [book]. • det(det(the)) --> [the]. • query (with an extra argument) • ?- sentence(P,List,[]). • P = parse tree • List = sentence s(np(det(the),man),vp(v(took),np(det(the),man)))

  10. Examples • query • what parse P corresponds to the sentence “the man took the book”? • ?- sentence(P,[the,man,took,the,book],[]). • P = s(np(det(the),man),vp(v(took),np(det(the),book))) ? ; • no • query • what are the possible parses P and word X for the sentence “the man took the X”? • ?- sentence(P,[the,man,took,the,X],[]). • P = s(np(det(the),man),vp(v(took),np(det(the),man))), • X = man ? ; • P = s(np(det(the),man),vp(v(took),np(det(the),book))), • X = book ? ; • no

  11. Examples • query • given a parse, what is the corresponding Sentence? • ?- sentence(s(np(det(the),man),vp(v(took),np(det(the),book))),Sentence,[]). • Sentence = [the,man,took,the,book] ? ; • no • query • supply no information, i.e. Parse and Sentence are both variables, • what are the possible sentences and parses? • ?- sentence(Parse,Sentence,[]). • Parse = s(np(det(the),man),vp(v(took),np(det(the),man))), • Sentence = [the,man,took,the,man] ? ; • Parse = s(np(det(the),man),vp(v(took),np(det(the),book))), • Sentence = [the,man,took,the,book] ? ; • Parse = s(np(det(the),book),vp(v(took),np(det(the),man))), • Sentence = [the,book,took,the,man] ? ; • Parse = s(np(det(the),book),vp(v(took),np(det(the),book))), • Sentence = [the,book,took,the,book] ? ; • no

  12. Printing of Answers • http://www.swi-prolog.org/FAQ/AllOutput.html

  13. Printing of Answers

  14. Printing of Answers

  15. Exercise • Construct a grammar that produces parsetree representationsfor: • I saw the boy with a telescope (2 parses) • the boy with a telescope saw me (1 parse) • remember: your grammar should allow for PP attachment to VP or NP • let’s use lowercase i to represent the first person pronoun (I) to sidestep problems with variables vs. symbols in SWI Prolog

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