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

Relating Words and Concepts

Words Concepts

Surface propertiesMorphological Some properties, e.g. numberSpellingPronunciation

Grammatical functionPart of speech Objects, actions, events,

propertiesSubcategorization "

Meaning Taxonomic relationsInference rules

Register Discourse conventions

One to Many Mappings

Homonyms(same spelling, same pronounciation,different meanings)

spring

One to Many Mappings

Homographs(same spelling,different pronounciation,same meaning)

bass

One to Many Mappings

Homophones(different spelling,same pronounciation,different meanings)

night

knight

http://www.cooper.com/homophonezone/

One to Many Mappings

Polysemy(multiple relatedmeanings)

knight

Many to One MappingsSynonymy

foodnourishmentgrub

SynsetsThe 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/

Other Relations Among Words

Hyponymy

animal

mammal

horse

horse is a hyponym of mammal and animal.

mammal is a hypernym of horse.

The Same Thing for Verbs

Troponymy

go

walk

shuffle amble swagger march

walk is a troponym of go.

Another Relation between Words

Meronymy

Nouns: brim and crown are meronyms of hat

Verbs: step is a meronym of walk

WordNet

http://www.cogsci.princeton.edu/~wn/

WordNet Sense Distribution

Maybe We Need to Represent Relationships Among Concepts, not Words

weightless

light

pale

Maybe We Need to Represent Relationships Among Concepts, not Words

OntologyThe 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/)

An Example of an Ontology

Penman (Generalized) Upper Model:

http://www.darmstadt.gmd.de/publish/komet/gen-um/node9.html

What are the Real Differences between Words and Concepts?

Concepts without words (e.g., schadenfreude, or <the gook that builds up around the top of a ketchup bottle>)

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.

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.

What Classes Should an Ontology Contain?

•Use words as the concepts. WordNet synsets do this.

•Use words plus some general concepts for which we don’t have words:

•SAYING&SENSING in the Upper Model

•Psychological Feature in WordNet

•Create new primitives and break words down into them:

•Conceptual Dependency

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.

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

John MOVE foot Loc(ball)

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 we’re interested in MT?

Thematic Roles

A middle ground:

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.

Mapping Words to Meanings

FrameNet (http://www.icsi.berkeley.edu/~framenet/)

Conceptual Dependency

One Important Issue – Lexicons Change all the Time

As new concepts emerge:

http://www.ananova.com/news/story/sm_801230.html?menu=news.technology.email

As new expressions for old concepts emerge: 24/7