Lexical Semantics

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Lexical Semantics
Read J M Chapter 16.
The task of classifying all the words of
language, or what's the same thing, all the ideas
that seek expression, is the most stupendous of
logical tasks. Anybody but the most accomplished
logician must break down in it utterly and even
for the strongest man, it is the severest
possible tax on the logical equipment and
faculty. Charles Sanders Peirce, letter to
editor B. E. Smith of the Century Dictionary
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Relating Words and Concepts
Words Concepts Surface properties Morphologi
cal Some properties, e.g. number Spelling Pron
unciation Grammatical function Part of
speech Objects, actions, events,
properties Subcategorization
" Meaning Taxonomic relations Inference
rules Register Discourse conventions
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One to Many Mappings
Homonyms (same spelling, same pronounciation, dif
ferent meanings) spring
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One to Many Mappings
Homographs (same spelling, different
pronounciation, same meaning) bass
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One to Many Mappings
Homophones (different spelling, same
pronounciation, different meanings) night kni
ght
http//www.cooper.com/homophonezone/
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One to Many Mappings
Polysemy (multiple related meanings) knight
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Many to One Mappings
Synonymy food nourishment grub
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Synsets
The largest synset in WordNet is buttocks, nates,
 arse, butt, backside, bum, buns, can, fundament, 
hindquarters, hind end, keister, posterior, prat, 
rear, rear end, rump, stern, seat, tail, tail end,
 tooshie, tush, bottom, behind, derriere,
 fanny, ass The next is dohickey, dojigger,
doodad, doohickey, gimmick, hickey, gizmo, gismo,
gubbins, thingamabob, thingumabob, thingmabob,
thingamajig, thingumajig, thingmajig, thingummy
      
http//www.cogsci.princeton.edu/wn/
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Other Relations Among Words
Hyponymy animal mammal horse horse
is a hyponym of mammal and animal. mammal is a
hypernym of horse.
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The Same Thing for Verbs
Troponymy go walk shuffle amble swag
ger march walk is a troponym of go.
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Another Relation between Words
Meronymy Nouns brim and crown are meronyms of
hat Verbs step is a meronym of walk
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WordNet
http//www.cogsci.princeton.edu/wn/
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WordNet Sense Distribution
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Maybe We Need to Represent Relationships Among
Concepts, not Words
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Maybe We Need to Represent Relationships Among
Concepts, not Words
weightless light pale
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Ontology
The subject of ontology is the study of the
categories of things that exist or may exist in
some domain. The product of such a study, called
an ontology, is a catalog of the types of things
that are assumed to exist in a domain of interest
D from the perspective of a person who uses a
language L for the purpose of talking about D.
The types in the ontology represent the
predicates, word senses, or concept and relation
types of the language L when used to discuss
topics in the domain D. An uninterpreted logic,
such as predicate calculus, conceptual graphs, or
KIF, is ontologically neutral. It imposes no
constraints on the subject matter or the way the
subject may be characterized. By itself, logic
says nothing about anything, but the combination
of logic with an ontology provides a language
that can express relationships about the entities
in the domain of interest. An informal ontology
may be specified by a catalog of types that are
either undefined or defined only by statements in
a natural language. A formal ontology is
specified by a collection of names for concept
and relation types organized in a partial
ordering by the type-subtype relation. Formal
ontologies are further distinguished by the way
the subtypes are distinguished from their
supertypes an axiomatized ontology distinguishes
subtypes by axioms and definitions stated in a
formal language, such as logic or some
computer-oriented notation that can be translated
to logic a prototype-based ontology
distinguishes subtypes by a comparison with a
typical member or prototype for each subtype.
Large ontologies often use a mixture of
definitional methods formal axioms and
definitions are used for the terms in
mathematics, physics, and engineering and
prototypes are used for plants, animals, and
common household items. - John Sowa
(http//www.jfsowa.com/ontology/)
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An Example of an Ontology
Penman (Generalized) Upper Model http//www.darms
tadt.gmd.de/publish/komet/gen-um/node9.html
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What are the Real Differences between Words and
Concepts?
Concepts without words (e.g., schadenfreude, or
ltthe gook that builds up around the top of a
ketchup bottlegt) Many to many mappings Surface
linguistic facts, such as subcategorization
frames I gave the book to John. I
donated the book to John. I gave John the
book. I donated John the book. I was mad
at John. I was angry at John. I was sore at
John. I was livid at John.
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Linguistic Facts are More Arbitrary than World
Knowledge
John gave/sent/read Bill the book. John
donated/returned/transferred Bill the book. One
possible explanation Give, send, and read come
to English through German. Donate, return, and
transfer come to English from Latin.
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What Classes Should an Ontology Contain?

• Use words as the concepts. WordNet synsets do
  this.
• Use words plus some general concepts for which we
  dont have words
• SAYINGSENSING in the Upper Model
• Psychological Feature in WordNet
• Create new primitives and break words down into
  them
• Conceptual Dependency

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Representing Events and Relationships
Many nouns have a straightforward semantics The
noun corresponds to a set of objects in the
world. Examples cat, apple, car. Many
adjectives can also be represented as sets of
things that possess some property red, fuzzy,
sharp. But most verbs, as well as many nouns,
adjectives, and adverbs, represent events and
relationships that have internal structure John
gave Bill the book before he left for school.
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How Close to the Surface Should We Stay?
John kicked the ball. (1) ?e,x isa(e,kicking) ?
kicker(e,John) ? kicked-obj(e,x) ?
isa(x,ball) (2) ?e,x isa(e,kicking) ?
agent(e,John) ? AE(e,x) ? isa(x,ball) (3) John ?
PROPEL ? ball
Loc(ball)
John ? MOVE ? foot ?
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When is Deep Meaning Worthwhile?
Much of the early work on CD was for story
comprehension. We need deep meaning if we want
to be able to answer questions like, What
moved? But suppose were interested in MT?
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Thematic Roles
A middle ground
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Mapping Surface Forms to Thematic Roles
Priority for subject assignment AGENT,
INSTRUMENT, THEME Sue cooked the potatoes. The
steam cooked the potatoes. The potatoes
cooked. Mary cooked. How to assign roles?
Selectional restrictions.
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Mapping Words to Meanings
FrameNet (http//www.icsi.berkeley.edu/framenet/
) Conceptual Dependency
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One Important Issue Lexicons Change all the Time
As new concepts emerge http//www.ananova.com/new
s/story/sm_801230.html?menunews.technology.email
As new expressions for old concepts emerge
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