Computational
Linguistics
Summer 2020
CSC 485
2b
2b. Syntax and Interpretation
Gerald Penn
Department of Computer Science, University of Toronto
Reading: Jurafsky & Martin: 12.3.4–6, 15.0–3; [Allen: 4.1–5]; Bird et al: 9.
Copyright © 2020 Suzanne Stevenson, Graeme Hirst and Gerald Penn. All rights reserved.
Goal of parsing
• A representation of properties relevant to meaning and interpretation:
• Things
• Predicates (events)
• Roles
Entities (e.g., in a knowledge base) Relations between things and predicates.
• Syntactic structure helps in:
• Determining things and predicates.
• Determining mapping of things to roles of predicates.
2
Example
The goalie kicked the ball. Event: kicked
Role: Agent (doer)
Thing: The goalie
kick (agent=goalie, theme=ball)
Thing: the ball
Role: Theme (thing affected)
3
Syntax ↔ interpretation
•
Mapping from structure to objects of interpretation
•
• Things:
• Predicates:
• Roles:
What are the roles in these examples?
Sara left.
Joan found the treasure in the garage. Ken put the ball in the garage.
Tim cut the wire with a pair of scissors. Melissa visited Ottawa with Nadia. Andrew felt like a failure.
NPs, Ss
verbs, preps, APs
??
4
Syntax ↔ interpretation
•
Mapping from structure to objects of interpretation
•
• Things:
• Predicates:
• Roles:
What are the roles in these examples?
Ken put the ball in the garage.
Joan found the treasure in the garage. Tim cut the wire with a pair of scissors. Melissa visited Ottawa with Nadia. Sara left.
Andrew felt like a failure.
NPs, Ss
verbs, preps, APs
?? (thematic roles)
5
Syntax ↔ thematic roles
•
Parse trees more or less indicate grammatical function:
Subject ≈ Agent
Object ≈ Theme
Object of preposition ≈ Goal/Location/Recipient
S
NP VP Agent
V Theme NP PP Goal/Location/Recipient
This mapping is used to determine appropriate semantic representation.
•
6
Case vs.Grammatical function vs.Thematic role
•
Mapping from case to grammatical function is
entirely regular (in English, but not 1-to-1): Subject: nominative/subjective
Object: accusative/objective
Object of preposition: accusative/objective
Mapping from grammatical function to thematic role is more or less regular:
Subject ≈ Agent / Experiencer
Object ≈ Theme
Object of preposition ≈ Goal/Location/
Recipient / Instrument
The latter mapping is used to determine appropriate semantic representation. 7
•
•
Verb subcategorization
•
Problem: Constraints on individual verbs and their complements not at all regular.
Nadia told / instructed / *said / *informed Ross to sit down. Nadia *told / *instructed / said / *informed to sit down. Nadia told / *instructed / *said / informed Ross of the
requirement to sit down.
Nadia gave / donated her painting to the museum. Nadia gave / *donated the museum her painting.
Nadia put / ate the cake in the kitchen. Nadia *put / ate the cake.
We will return to this later…
•
8
Diathesis 1
The goalie kicked the ball. Event: kicked
Role: Agent (doer)
Thing: the goalie
kick (agent=goalie, theme=ball)
Thing: the ball
Role: Theme (thing affected)
9
Diathesis 2
The ball was kicked. Event: kicked
Role: Theme (thing affected)
Thing: the ball
kick (agent=?, theme=ball)
10
Diathesis 3
The ball was kicked by the goalie. Event: kicked
Role: Theme (thing affected)
Thing: the ball
kick (agent=goalie, theme=ball)
Thing: the goalie
Role: Agent (doer)
11
Diathetic alternation
the goalie kicked the ball
12
Diathetic alternation
From object position in VP to subject position in S
the ball was kicked by the goalie
From subject position in S to PP in VP
But the semantic representation doesn’t change
13