ling 388 language and computers lecture 18 10/30/03 sandiway fong

LING 388Language and Computers

Lecture Lecture 1818

10/3010/30/03/03

Sandiway FONGSandiway FONG

Administrivia

Computer Laboratory next time as well …Computer Laboratory next time as well … November 4th in SBS 224November 4th in SBS 224

Homework 4Homework 4 3 exercises today3 exercises today 1 extra-credit question1 extra-credit question Homework 4 continues next timeHomework 4 continues next time

Lecture 17 slides updated…Lecture 17 slides updated… Added an appendix illustrating the use of negation to Added an appendix illustrating the use of negation to

implement counting up to 2 instead of the extra argument implement counting up to 2 instead of the extra argument method [method [from suggestion in classfrom suggestion in class]]

Exercise 1: Relative Clauses

Examples:Examples: The cat that John sawThe cat that John saw (object)(object) The cat that saw JohnThe cat that saw John (subject)(subject)


Sample DCG:Sample DCG: s(s(X,Y)) --> np(X), vp(Y).s(s(X,Y)) --> np(X), vp(Y). vp(vp(X,Y)) --> transitive_verb(X), np(Y).vp(vp(X,Y)) --> transitive_verb(X), np(Y). np(np(X)) --> proper_noun (X).np(np(X)) --> proper_noun (X).% % Special rules for relative clausesSpecial rules for relative clauses np(np(np(Y,Z),U)) --> det(Y), common_noun(Z), sbar(U).np(np(np(Y,Z),U)) --> det(Y), common_noun(Z), sbar(U). np(np(x)) --> [].np(np(x)) --> []. sbar(lambda(x,Y)) --> complementizer, s(Y).sbar(lambda(x,Y)) --> complementizer, s(Y). complementizer --> [that].complementizer --> [that].% % LexiconLexicon transitive_verb(v(hit)) --> [hit].transitive_verb(v(hit)) --> [hit]. transitive_verb(v(saw)) --> transitive_verb(v(saw)) -->

[saw].[saw]. proper_noun(john) --> [john]. proper_noun(john) --> [john]. proper_noun(mary) --> [mary].proper_noun(mary) --> [mary]. common_noun(n(man)) --> [man].common_noun(n(man)) --> [man]. common_noun(n(cat)) --> [cat]. common_noun(n(cat)) --> [cat]. det(det(the)) --> [the].det(det(the)) --> [the].


Consult DCGConsult DCG Parsing noun phrases (NPs):Parsing noun phrases (NPs):

Run queriesRun queries?- np(X,[the,cat,that,john,saw],[]).?- np(X,[the,cat,that,john,saw],[]).?- np(X,[the,cat,that,saw,john],[]).?- np(X,[the,cat,that,saw,john],[]).

Verify DCG also (incorrectly) accepts as NPs:Verify DCG also (incorrectly) accepts as NPs: *The cat that John saw Mary*The cat that John saw Mary *The cat that saw*The cat that saw


Pseudo-Logical Form for Pseudo-Logical Form for the cat that John sawthe cat that John saw::np

np

det

the

n

cat

lambda

x s

np

np vp

vjohn

saw x


Homework Question (A):Homework Question (A): Modify the DCG to accept the omission of the Modify the DCG to accept the omission of the

complementizer complementizer that that for object relative clausesfor object relative clauses Your DCG should accept both of the following:Your DCG should accept both of the following:

the cat John sawthe cat John saw the cat that John sawthe cat that John saw

as NPsas NPs Hint:Hint:

Write an empty category rule in place of the complementizerWrite an empty category rule in place of the complementizer


Parsing complete sentences:Parsing complete sentences: Run queries:Run queries:

?- s(X,[mary,hit,the,cat,that,john,saw],[]).?- s(X,[mary,hit,the,cat,that,john,saw],[]).?- s(X,[mary,hit,the,cat,that,saw,john],[]).?- s(X,[mary,hit,the,cat,that,saw,john],[]).

Verify the DCG also (incorrectly) accepts as Verify the DCG also (incorrectly) accepts as sentences:sentences: *Mary hit*Mary hit *hit John*hit John *hit*hit


Multiple EmbeddingsMultiple Embeddings Add ruleAdd rule

transitive_verb(v(hissed_at)) --> [hissed,at].transitive_verb(v(hissed_at)) --> [hissed,at]. Turn on full printing (Turn on full printing (taken from Lecture 4taken from Lecture 4))

?- set_prolog_flag(toplevel_print_options,[max_depth(0)]).?- set_prolog_flag(toplevel_print_options,[max_depth(0)]).

Run query forRun query for Mary hit the man that the cat that John saw hissed atMary hit the man that the cat that John saw hissed at


Homework Question (B):Homework Question (B): The previous sentenceThe previous sentence

Mary hit the man that the cat that John saw hissed atMary hit the man that the cat that John saw hissed at

has a doubly-embedded object relative clause has a doubly-embedded object relative clause structure:structure:

Mary hit [Mary hit [NPNP[[NPNP the man the manii] that [] that [NPNP[[NPNP the cat the catjj] that ] that

John saw [John saw [NPNP eejj]] hissed at []] hissed at [NPNP eeii]]]]


Homework Question (B) contd.:Homework Question (B) contd.: WithoutWithout any further modification to the DCG, construct any further modification to the DCG, construct

and show parses for:and show parses for: A sentence with two levels of embedding using subject relative A sentence with two levels of embedding using subject relative

clausesclauses A sentence with two levels of embedding using one subject A sentence with two levels of embedding using one subject

and one object relative clauseand one object relative clause Any sentence with a triply-embedded relative clause structureAny sentence with a triply-embedded relative clause structure

Notes: Notes: i.e. you cannot add any rules or words to the DCG so fari.e. you cannot add any rules or words to the DCG so far The DCG only allows Det N sequences in relative clause The DCG only allows Det N sequences in relative clause

constructions, i.e. you have to make do without NP -> Det Nconstructions, i.e. you have to make do without NP -> Det N

Extra Credit Homework Question

Answer for Exercise 1 Part (A) will also allow the Answer for Exercise 1 Part (A) will also allow the complementizer to be dropped (incorrectly) for complementizer to be dropped (incorrectly) for subject relative clauses:subject relative clauses: the cat that saw Johnthe cat that saw John *the cat saw John*the cat saw John ((as a complex NPas a complex NP))

Extra Credit Homework Question

Modify the DCG to allow Modify the DCG to allow thatthat to be omitted to be omitted onlyonly in the case of object relative clauses, i.e. grammar in the case of object relative clauses, i.e. grammar should still accept:should still accept: the cat John sawthe cat John sawbut reject its subject relative clause counterpart:but reject its subject relative clause counterpart: *the cat saw John*the cat saw John

Hint (Hint (for one possible implementationfor one possible implementation):): Look at how subject/verb agreement was enforcedLook at how subject/verb agreement was enforced

Exercise 2: Disjunctive Tree-Walker

Tree-walker template (disjunctive form):Tree-walker template (disjunctive form): visit(X) :- visit(X) :-

X =.. [_,A1,_],X =.. [_,A1,_], visit(A1).visit(A1).

visit(X) :- visit(X) :- X =.. [_,_,A2],X =.. [_,_,A2], visit(A2).visit(A2).

visit(X) :-visit(X) :- X =.. [_,A],X =.. [_,A], visit(A).visit(A).

visit(X) :- atom(X).visit(X) :- atom(X). Note: Note:

used underscores to substitute for variables that are only used underscores to substitute for variables that are only mentioned oncementioned once


Let’s modify visit/1 to look for Let’s modify visit/1 to look for JohnJohn only: only: visit(X) :- visit(X) :-




visit(X) :- atom(X).visit(X) :- atom(X). <- <- to be substituted byto be substituted by - - visit(john).visit(john).


Consult visit/1Consult visit/1 Make sure DCG is still loaded Make sure DCG is still loaded ?- listing. ?- listing. to checkto check

Turn on tracing for visit/1 onlyTurn on tracing for visit/1 only ?- spy(visit/1).?- spy(visit/1).

Run the query:Run the query: ?- s(X,[mary,hit,the,cat,that,hissed,at,john],[]), visit(X).?- s(X,[mary,hit,the,cat,that,hissed,at,john],[]), visit(X). Step through debugger using the command Step through debugger using the command ll (leap) (leap) Prolog should succeed and report X.Prolog should succeed and report X.


Test the structures for sentences: Test the structures for sentences: Mary hit the cat that hissed at MaryMary hit the cat that hissed at Mary

Query should failQuery should fail John saw the cat that saw JohnJohn saw the cat that saw John

Query should succeed twiceQuery should succeed twice


Homework Question:Homework Question: Modify visit/1 to search for all NP nodesModify visit/1 to search for all NP nodes How many times should visit/1 succeed for the How many times should visit/1 succeed for the

following sentence?following sentence? Mary hit the cat that hissed at JohnMary hit the cat that hissed at John

Hint:Hint: You’ll need to add more than one clause to visitYou’ll need to add more than one clause to visit//11

Exercise 3: Collecting Answers

Instead of entering Instead of entering ;; (possibly repeated) to the Prolog (possibly repeated) to the Prolog interpreter …interpreter … we can used a higher-order predicate findall/3 to collect we can used a higher-order predicate findall/3 to collect

together all possible answers to a querytogether all possible answers to a query findall/3findall/3

Prolog build-in Prolog build-in Usage:Usage:

findall(X,Query,List)findall(X,Query,List)• XX may be a variable or constant or structure bound once may be a variable or constant or structure bound once

per successful call to per successful call to QueryQuery• QueryQuery is the Prolog query we wish to test (minus is the Prolog query we wish to test (minus ?-?- and and ..))• ListList is the collected list of values of is the collected list of values of XX per successful call per successful call


Example:Example: male(john).male(john). male(pete).male(pete). female(mary).female(mary). female(jill).female(jill). human(X) :- female(X) ; male(X).human(X) :- female(X) ; male(X). ( ; ( ; indicates disjunctionindicates disjunction))

Prolog query:Prolog query: ?- human(X).?- human(X).

X = mary ;X = mary ; X = jill ;X = jill ; X = john ;X = john ; X = pete ;X = pete ; NoNo


Using findall/3:Using findall/3: ?- findall(X,human(X),List).?- findall(X,human(X),List).

X = _G283X = _G283 ((an internally generated variablean internally generated variable)) List = [mary,jill,john,pete] ;List = [mary,jill,john,pete] ; NoNo

length/2length/2 Prolog built-inProlog built-in Usage:Usage:

length(List,N)length(List,N)• ListList is a list is a list• NN is bound to the number of elements in is bound to the number of elements in ListList

ExampleExample:: ?- findall(X,human(X),List), length(List,N).?- findall(X,human(X),List), length(List,N).

N = 4N = 4


Basic (unmodified) disjunctive tree-walker:Basic (unmodified) disjunctive tree-walker: visit(X) :- visit(X) :-




visit(X) :- atom(X).visit(X) :- atom(X).


Homework Question:Homework Question: Assuming the unmodified version of visit/1Assuming the unmodified version of visit/1 What does the queryWhat does the query

?- s(X,[mary,hit,the,cat,that,hissed,at,john],[]),?- s(X,[mary,hit,the,cat,that,hissed,at,john],[]), findall(once,visit(X),L), findall(once,visit(X),L),

length(L,N).length(L,N).do?do?

ling 388 language and computers lecture 18 10/30/03 sandiway fong

Documents

cat john

john saw mary

object relative clauses

relative clauses sample

relative clauses examples

subject relative clauses

relative clauses npnpnpy

john saw np e j