Sandiway Fong Lecture 15 Homework 5 Other kinds of recursion eg Relative clauses the cheese that the rat ate the cheese that the rat that the cat saw ate the cheese that the rat that the cat ID: 237289
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Slide1
LING 388: Language and Computers
Sandiway
Fong
Lecture 15Slide2
Homework 5
Other kinds of recursion, e.g.
Relative clauses
the cheese that the rat atethe cheese that the rat that the cat saw atethe cheese that the rat that the cat that the dog chased saw ate
these are not complete sentences, but just noun phrases (NPs)Slide3
Homework 5
Example:
the cheese that the rat
ate
np
(
np
(
np(D,N),SBAR)) --> det(D), nn(N), sbar(SBAR).nn(nn(rat)) --> [rat].nn(nn(cheese)) --> [cheese].v(v(ate)) --> [ate].np(np(0)) --> [].
Alternatively:5. vp(vp(V)) --> v(V).Slide4
Homework 5
Example:
the cheese that the rat
that the cat saw ate
nn
(
nn
(cat)) --> [cat]
.
v(v(
saw
)) --> [
saw
]
.Slide5
Homework 5
Example:
the cheese that the rat
that the cat saw ate
vp
(
vp
(V)) --> v(V).
versionSlide6
Homework 5 review
Example:
the cheese that the rat that the cat
that the dog chased saw ate
nn
(
nn
(dog)) --> [dog]
.v(v(chased)) --> [chased].Slide7
Subject Relative Clauses
Subject relative
clauses (not
center-embedded)the cat that saw the rat that saw the cheese that …[NP the cat [SBAR
that [
S
saw [
NP
the rat [SBAR that [S saw [NP the cheese that … ]]]]]]]the rat that Ø saw the cheesethe cat that Ø saw the rat that Ø saw the cheesethe dog that Ø saw the cat that Ø saw the rat that Ø saw the cheeseSlide8
Subject Relative Clauses
Subject relative
clauses (not
center-embedded)the rat that Ø saw the cheese
Advantage of the empty category rule
np
(
np
(0)) --> [].over thevp(
vp(V)) --> v(V).version(However, there are disadvantages too…)Slide9
Subject Relative Clauses
Subject relative
clauses (not
center-embedded)the cat that Ø saw the rat that Ø
saw the
cheeseSlide10
Subject Relative Clauses
Subject relative
clauses (not
center-embedded)the dog that Ø saw the cat that Ø
saw the rat that
Ø
saw the
cheeseSlide11
Subject Relative Clauses
Subject relative
clauses (not
center-embedded)the dog that Ø saw the cat that Ø
saw the rat that
Ø
saw the
cheeseSlide12
The empty category rule
A disadvantage of the grammar rule
np
(np(0)) --> [
]
:
Example:
*the rat that saw
freely permits the simultaneous omission
of the subject and the object
*the rat that Ø saw ØSlide13
The empty category rule
Rule is too permissive,
let’s verify
that it permits ungrammatical sentences such as:John saw MaryØ saw MaryJohn saw Ø
Ø
saw
ØSlide14
Complexity and Comprehension
Subject and Object Relative
Clauses
From easy to hard to comprehend for humans?Subject relative + subject relative Subject relative + object relative
Object relative + subject relative
Object relative + object relative
For a computer, no difference…Slide15
Subject and Object Relative Clauses
Subject relative
+ subject relative
the cat that Ø chased the dog that Ø ate the cheese saw the ratSlide16
Subject and Object Relative Clauses
Subject relative
+ object relative
the
cat that
Ø
saw the rat that the dog chased
Ø ate the cheeseSlide17
Subject and Object Relative Clauses
Object relative + subject relative
the
cat that
the dog that
Ø
saw the rat chased
Ø
ate the cheeseSlide18
Subject and Object Relative Clauses
Object relative + object relative
the
cat that
the dog that the rat saw
Ø
chased
Ø
ate the cheeseSlide19
Class Exercise 1
Grammar rule:
np(np(0)) --> [].
permits subjects and objects to be
freely
omitted
Subject
relative clausesthe rat that Ø saw the cheesethe cat that Ø saw the rat that Ø saw the cheesethe dog that Ø saw the cat that Ø saw the rat that Ø saw the cheeseObject relative clausesthe cheese that the rat ate Øthe cheese that the rat that the cat saw Ø ate Øthe cheese that the rat that the cat that the dog chased Ø saw Ø ate ØSlide20
Class Exercise 1
Rule is too permissive, verify that it permits ungrammatical sentences:
John saw Mary
Ø saw MaryJohn saw Ø
Ø
saw
Ø
Thus it also permits:
the cheese that the rat ate Øthe cheese that Ø ate Øthe rat that Ø saw the cheesethe rat that Ø
saw Øthe cheese that the rat ate the cheese
the rat that the rat saw the
cheeseSlide21
Class Exercise 2
Let’s modify (or restrict) the grammar so that subject relative clauses force an empty subject only
the rat that
Ø saw the cheesethe rat that Ø saw
Ø
the rat that the rat saw the cheese
idea
: make this
sbar special to subject relative clauses,i.e. force subject NP to be empty and object NP to be overtSlide22
Class Exercise 2
First, delete the
overgenerating
rule… i.e. delete the empty category rule from the grammar.
❌
We are left with only rules for generating overt NPsSlide23
Class Exercise 2
Grammar rules involved:
(Rename rule)Slide24
Class Exercise 2
Do copy and rename:
Rename nonterminal (S)Slide25
Class Exercise 2
Do copy and rename:
Rename nonterminal (
sbar
)Slide26
Class Exercise 2
Verify subject
relative clauses force an empty subject only
the rat that Ø saw the cheesethe rat that Ø saw
Ø
the rat that the rat saw the cheese