"Building Semantic Representations"
The Stone World Program:
1. User-interface to a robot-like agent in a microworld.
2. Uses an ATN and a semantic grammar.
3. Stylized model of space
(2-D, cellular).
Augmented Transition Networks
1. Chart-oriented
2. Reminiscent of finite-state automata and pushdown automata
3. Capable of arbitrary computation
4. Each transition corresponds to a syntactic unit (phrase)
5. Semantic analysis is performed
as arcs are traversed.
Case Frames
1. A type of frame (in the sense of Minsky) -- a structure that brings together a collection of objects called slot fillers. The fields for these fillers are the slots.
2. A case frame is verb-oriented. The set of slots relevant to the event is established by the verb of a sentence.
3. Each slot holds an object represented by a noun in the sentence (or a pronoun, or by something not explicit in the sentence).
4. Each slot is marked with a "role" that corresponds to a generalized case. Grammatical cases are "nominative", "objective", "dative", etc.
Generalized cases include....
Agent
Co-agent
Source
Destination
Recipient
Beneficiary
Vehicle
Tool
Direct object
Time
Location
Object in related location
Semantics of Time
Relative time
Relative to the present:
Past, present, future
Relative to an event
in the past.
Relative to an event
in the future.
Absolute time
Dates, hours, time
zones, calendars.
Events vs Processes
"It happened."
"It was going on"
"It is going on"
"It had been going
on."
Periodic events
"Every Monday"
"Once a year"
Semantics of Space
Settings for events -- location
in terms of spatial relationships with objects.
"At school."
"Behind the fence."
Prepositions of space:
On, above, below, behind,
in front of, next to, left of, to the left of, near, ...
Size, distance,
path,
shape.
Motion -- path with time (trajectory).
Introducing New Objects and Referring to Old Ones
Language for introduction:
1. indefinite article.
"A man walked over to me."
2. equivalent vernacular
expression. "Like there's this man that walks over to me."
3. more formal introduction:
"Thomas Jefferson was a statesman from Virginia."
4. intro. with numerical
quantification: "Five cats ran under a car."
Language for references:
1. pronouns: "He spoke
softly."
2. definite article:
"The man carried a book."
Correctly linking references with the objects introduced earlier is a significant challenge of NLU.
One method is to link a pronoun
to the most recently introduced object that is "compatible" with it.
For example, consider this...
"Ann and John went to the
store. She drove the car."
She probably refers
to Ann, and not John.
Last modified: November 25, 1998
Steve Tanimoto