INTRODUCTION TO ARTIFICIAL
INTELLIGENCE
Massimo Poesio
LECTURE 6
The Cognitive Perspective: Generative
Lexicon
Sense Enumeration Lexicon (SEL)
• WordNet and similar resources are examples of SENSE
ENUMERATION LEXICA
• Direct approach to handle polysemy is to allow the lexicon to
have multiple listing of words, each annotated with a separate
meaning or lexical sense.
• Widely accepted in both computational and theoretical
linguistics.
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Sense Enumeration Lexicon (SEL)
• Example of Contrastive Senses
bank1
CAT= count-noun
GENUS= financial-institution
bank2
CAT= count-noun
GENUS= shore
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Verbal polysemy in sense enumeration
lexica
Syntactic polysemy deals with polivalency (I), object deletion (II) and the
general properties of argument expression (III).
(I) a. Mary began to read the novel.
b. Mary began reading the novel.
c. Mary began the novel.
(II) a. Mary ate (her meal) quickly.
b. Mary devoured *(her meal) quickly.
(III) a. John carved a doll (out of the wood).
b. John carved the wood (into a doll).
Nominal polysemy
(1)a. Mary doesn’t believe the book.
b. John sold his books to Mary.
(2)a. Eno the cat is sitting on yesterday’s newspaper.
b. Yesterday’s newspaper really got me upset.
(3)a. Mary is in Harvard Square looking for the Bach sonatas.
b. We won’t get to the concert until after the Bach sonatas.
(4)a. I have my lunch in the backpack.
b. Your lunch was no longer today than it was yesterday.
(5)a. The phone rang during my appointment.
b. My next appointment is John.
Nominal polysemy in sense enumeration
lexica
• Newspaper
Newspaper1
CAT= count-noun
GENUS= artefact
Newspaper2
CAT= count-noun
GENUS= information
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GENERATIVE LEXICON THEORY
• (Pustejovsky, 1991, 1995)
• Claim: the concepts associated with a word in
a context are GENERATED by a process starting
from lexical entries structured into QUALIA
STRUCTUREs and involving GENERATIVE
DEVICES such as TYPE COERCION and COCOMPOSITION
Generative lexicon theory: lexical entries
A lexical entry in the generative lexicon consists of the
following elements at least:
•
Argument Structure
 True Arguments
 Default Arguments
 Shadow Arguments
 True Adjuncts
•
Event Structure
•
Qualia Structure
 Formal
 Constitutive
 Telic
 Agentive
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QUALIA ROLES
Word meaning is structured on the basis of four generative
factors, called qualia roles, that capture how humans
understand objects and relations in the world and provide
the minimal explanation for the linguistic behavior of
lexical items.
FORMAL: the basic category that distinguishes an object
within a larger domain
CONSTITUTIVE: the relation between an object and its
constituent parts
TELIC: the object’s purpose and function
AGENTIVE: factors involved in the object’s origin or ‘coming to
being’
Qualia structures and argument
polysemy
Qualia Structure for novel
novel
Qualia
const = narrative
formal = book
telic = reading
agent = writing
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A generative device: type coercion
• Type Coercion
 a lexical item or phrase is coerced to a semantic interpretation by a
governing item in the phrase, without changing its syntactic type
Mary began to read the novel
Mary began reading the novel
Mary began the novel
•
• Function Application with Coercion
 different complement type of the verb
 different interpretations of the verb that arise for the different
complements
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Other generative devices
• Selective Binding
 a lexical item or a phrase operates specifically on the substructure of a phrase,
without changing the overall type in the composition
a good knife: a knife that cuts well
• Co-composition
 multiple elements within a phrase behave as functors, generating new nonlexicalized senses for the words in composition
John baked the potato
John baked the cake
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NOMINAL POLYSEMY
A dot object is a deeper structure relating the apparently contradictory
senses of the word. For each sense pair there is a relation that ‘connects’
the senses in a well-defined way.
The dot object is characterized as:
- a Cartesian type product of n types
(the product τ1 x τ2, of types τ1 and τ2, each denoting sets, is the ordered
pair <t1 , t2>, where t1 ε τ1 , t2 ε τ2)
- with some additional constraints: there exists a relation R between
the elements of τ1 and τ2 , namely, R(t1 , t2).
This relation must be seen as part of the definition of the semantics for
the
dot object.
Type combinations included in the broad range of complex types
encountered in natural language:
a.
b.
c.
d.
e.
phys_objinfo
: e.g., book, record
eventevent : e.g., construction, examination
eventquestion : e.g., exam
eventfood : e.g., lunch, dinner
eventhuman : e.g., appointment
For each of these type products, there is a unique relation, Ri, that
structures the types.
For example, nouns such as book or record, are structured by a
containment relation R (container-like concepts).
This containment relation -hold(x,y)- must be encoded directly into the
semantics of the concept as the FORMAL quale value.
The lexical structure for newspaper as a dot object is represented as
follows:
newspaper
ARGSTR =
ARG1 = y:information
ARG2 = x:phys_obj
QUALIA
=
informationphys_obj
FORM = hold(x,y)
TELIC = read(e,w,xy)
AGENT = write(e,v,xy)
This translates to the following logical expression:
λx yev[newspaper (x:physobj  y :info)  hold(x,y) 
λwλe [read (e,w,xy)  [write(e;v,x y)]]
REFERENCES
• Pustejovsky, J. (1995). The generative Lexicon.
Cambridge, MA: MIT Press.