1. Lecture – VIII Monojit Choudhury RS, CSE, IIT Kharagpur
GRAMMAR – II From Syntax to Meaning Communication Empowerment Laboratory, IIT Kharagpur
Lecture – VIII
Monojit Choudhury
RS, CSE, IIT Kharagpur
14th Feb 2005
CEL, IIT Kharagpur

2. The Big Picture Source Language Analysis Target Language Generation
Text Normalization
Text Rendering
Morphological Analysis
Morphological Synthesis
POS Tagging
Phrase Generation
Parsing
Role Ordering
Semantic Analysis
Lexical Choice
Discourse Analysis
Discourse Planning
14th Feb 2005
CEL, IIT Kharagpur

3. Recap Rationalism vs. Empiricism Modelling English using CFG
Regular Languages are insufficient
Even CFG cannot model English purely
Advantages
Captures most of the things
Efficient parsing algorithms
Problems
Structural Ambiguity
Agreement Constraints
14th Feb 2005
CEL, IIT Kharagpur

4. But what to do with the parse trees??!!!
Parsing
Surface Form
Deep Structure
PARSER
Word Tag
Pairs
All possible
parse trees
But what to do with the parse trees??!!!
Grammar
Rules
14th Feb 2005
CEL, IIT Kharagpur

5. Parse Trees Who like fresh fruits? What do children like?
Do children like fresh fruits? VP NP NP N V A N
Children like fresh fruits
14th Feb 2005
CEL, IIT Kharagpur

6. Parse Trees Who like fresh fruits? What do children like?
Do children like fresh fruits? VP NP PP
Aux V
Pre A N N
Fresh fruits are liked by children
14th Feb 2005
CEL, IIT Kharagpur

7. Grammatical Functions
Apart from the Phrase Structure in PSG, there are also Grammatical Functions
Specifies the relation of the NP with the verb.
Subject, Object1, Object2, ...
Children like fresh fruits.
Their mother gave them some apples.
14th Feb 2005
CEL, IIT Kharagpur

8. Active vs. Passive voice
Fresh fruits are liked by children.
They were given some apples.
Children like fresh fruits.
Their mother gave them some apples.
14th Feb 2005
CEL, IIT Kharagpur

9. Conclusions
In fixed word order languages, Grammatical Functions are dependent on the position of the NP relative to the verb.
Grammatical function, therefore, changes with the voice of the sentence.
Hence, it does not capture the semantics completely.
14th Feb 2005
CEL, IIT Kharagpur

10. Theta Roles Semantics is “unambiguously” captured using Theta roles
Agent, Co-agent/Patient, Instrument ...
The children cut the apples with a knife
The apples were cut by a knife
14th Feb 2005
CEL, IIT Kharagpur

11. “The stone rolled down.”
Ambiguity Again!
What characterizes Agent-ship/patient-ship?
“The stone rolled down.”
What should be an ideal set of theta roles?
Are Theta roles language independent?
The debate is primarily philosophical with some Engineering connotations.
14th Feb 2005
CEL, IIT Kharagpur

12. Lexical Functional Grammar
Joan Bresnan (Ed.) The Mental representation of Grammatical Relations, MIT press, 1982
Why lexical we will come to later.
Functional because it captures functional relations
c- structure and f-structure
14th Feb 2005
CEL, IIT Kharagpur

13. c-structure S S VP VP NP NP NP PP N V A N Aux V Pre A N N
Children like fresh fruits
Fresh fruits are liked by children
14th Feb 2005
CEL, IIT Kharagpur

14. Children like fresh fruits.
f-structure - I
Children like fresh fruits.
subject
Predicate ‘like’ ( subject,  object)
Tense present
Object
Predicate Child
Number Plural
Predicate fruit
Adjective fresh
Number plural
14th Feb 2005
CEL, IIT Kharagpur

15. Fresh fruits are liked by children.
f-structure - II
Fresh fruits are liked by children.
subject
Predicate ‘like’ ( by-object,  subject)
Tense present
by-Object
Predicate fruit
Adjective fresh
Number Plural
Predicate Child
Number Plural
14th Feb 2005
CEL, IIT Kharagpur

16. Formal Model R1: S  NP VP  subj =   =  R2: VP  V {NP} {NP} PP*
obj =  obj2 =  (pcase) = obj
R3: PP  prep NP
obj = 
14th Feb 2005
CEL, IIT Kharagpur

17. Lexicon Entries the, det spec = the children, noun pred = child
number = plural
14th Feb 2005
CEL, IIT Kharagpur

18. f-structure representation
Feature Structures
General Concept:
A declarative way of specifying constraints and contexts
Can model agreement and other context dependent features which are not modeled using CFG (Compare with types in C)
Can be defined at the lexical, syntactic, semantic levels
14th Feb 2005
CEL, IIT Kharagpur

19. Feature Structure FEATURE1 VALUE1 FEATURE2 VALUE2 FEATURE3 VALUE3.
AVM (Attribute Value Matrix) Representation
14th Feb 2005
CEL, IIT Kharagpur

20. Atomic vs. Nested Feature Structure
Category verb
Root run
TAM
Agreement
Category verb
Root run
Tense Past
Aspect Cont
Modality Default
Number Φ
Person Φ
Tense Past
Aspect Cont
Modality Default
Number Φ
Person Φ
“was running”
14th Feb 2005
CEL, IIT Kharagpur

21. Some Concepts Under-specification & Subsumption  Lattice
DAG representation  Feature Path
Reentrants
Typed Feature Structures and Type Hierarchy
Unification
14th Feb 2005
CEL, IIT Kharagpur