Symbols and Language Lexical Relations SIMS 202 Profs. Hearst & Larson UC Berkeley SIMS Fall 2000

Today l Symbols and Language l Lexical Relations

What is a symbol? l Something that stands for or suggests something else. l An arbitrary conventional sign used in writing or printing to represent: –Operations, quantities, elements, relations, qualities –(Merriam-Webster’s Collegiate) l What is meant by sign and represent?

Recognizing Symbols What is/are this/these symbol(s)? –Two overlapping squares? –Eight horizontal and eight vertical lines?

Symbols and Language l Abstract concepts are difficult to express in a computer. l Combinations of abstract concepts are even more difficult to express: –time –shades of meaning –social and psychological concepts –causal relationships

Symbols and Language The Dog.

Symbols and Language The Dog. The dog cavorts. The dog cavorted. The picture doesn’t really show the manner or tense.

Symbols and Language The man. The man walks.

Symbols and Language The man walks the cavorting dog. So far, we can sort of show the meaning in pictures.

Symbols and Language As the man walks the cavorting dog, thoughts arrive unbidden of the previous spring, so unlike this one, in which walking was marching and dogs were baleful sentinels outside unjust halls. What is the relation between the symbols and the meaning?

Symbols and Language l Language only hints at meaning. l Most meaning of text lies within our minds and common understanding. –“How much is that doggy in the window?” »how much: social system of barter and trade (not the size of the dog) »“doggy” implies childlike, plaintive, probably cannot do the purchasing on their own »“in the window” implies behind a store window, not really inside a window, requires notion of window shopping

Correspondences between Symbols and Meaning l Consider made-up languages –Codes used by espionage agents »“Pope” means a particular piece of microfilm »“Denver” indicates a particular mailbox l People remember the “gist” instead of the actual words used. –This implies the actual words used are not very salient; what matters is the meaning.

Semantics: The Meaning of Symbols l Semantics versus Syntax –add(3,4) –3 + 4 (different syntax, same meaning) l Meaning versus Representation –What a person’s name is versus who they are. »A rose by any other name... –What the computer program “looks like” versus what it actually does.

Semantics l Semantics: assigning meanings to symbols and expressions. –Usually involves defining: »objects »properties of objects »relations between objects –More detailed versions include »events »time »places »measurements (quantities)

The Role of Context l The concept associated with the symbol 21 means different things in different contexts. –Examples? l The question “Is there any salt?” –Asked of a waiter at a restaurant. –Asked of an environmental scientist at work.

What’s In a Sentence? “A sentence is not a verbal snapshot or movie of an event. In framing an utterance, you have to abstract away from everything you know, or can picture, about a situation, and present a schematic version which conveys the essentials. In terms of grammatical marking, there is not enough time in the speech situation for any language to allow for the marking of everything which could possibly be significant to the message.” Dan Slobin, in Language Acquisition: The state of the art, 1982

Lexical Relations

l Conceptual relations link concepts –Goal of Artificial Intelligence l Lexical relations link words –Goal of Linguistics l How do they differ?

Major Lexical Relations l Synonymy l Polysemy l Metonymy l Hyponymy/Hyperonymy l Meronymy l Antonymy

WordNet l A large lexical database l Developed over the last ten years l Started by George Miller –A new book out about it (Fellbaum 98) –Some nice interfaces available on the Web » » –Lexical Freenet – find links between words using Wordnet »

Synonymy l Different ways of expressing related concepts l Examples –cat, feline, Siamese cat l Overlaps with basic and subordinate levels l Synonyms are almost never truly substitutable: –Used in different contexts –Have different implications »This is a point of contention.

Polysemy l Most words have more than one sense –Homonym: same word, different meaning »bank (river) »bank (financial) –Polysemy: different senses of same word »That dog has floppy ears./ »She has a good ear for jazz. »bank (financial) has several related senses l the building, the institution, the notion of where money is stored

Metonymy l Use one aspect of something to stand for the whole –The building stands for the institution of the bank. –Newscast: “The White House released new figures today.” –Waitperson: “The ham sandwich spilled his drink.”

Hyponymy/Hyperonymy l ISA relation l Related to Superordinate and Subordinate level categories –hyponym(robin,bird) –hyponym(bird,animal) –hyponym(emu,bird) l A is a hypernym of B if B is a type of A l A is a hyponym of B if A is a type of B

Meronymy l Parts-of relation –part of(beak, bird) –part of(bark, tree) l Transitive conceptually but not lexically: –The knob is a part of the door. –The door is a part of the house. –? The knob is a part of the house ?

Antonymy l Lexical opposites –antonym(large, small) –antonym(big, small) –antonym(big, little) –but not large, little l Many antonymous relations can be reliably detected by looking for statistical correlations in large text collections. (Justeson &Katz 91)

Thesauri keep track of meanings l Polysemy: same word, different senses of meaning –slightly different concepts expressed similarly l Synonyms: different words, related senses of meanings –different ways to express similar concepts l Thesauri help draw all these together

Important Distinction Lexical Relations vs. Conceptual Relations

Lexical vs. Conceptual People associate an adjective with its antonym on a lexical level (K. J. Miller ‘98) »Example: l Opposite of “large” is ___? l The answer is not “little”. »Standardized tests take advantage of this.

What is an Ontology?

Ontology l From Merriam-Webster’s Collegiate: –A branch of metaphysics concerned with the nature and relations of being. –A particular theory about the nature of being or the kinds of existence. l More prosaically: –A carving up of the world’s meanings. –Determine what things exist, but not how they inter-relate. l Related terms: –taxonomy, dictionary, category structure

Building an Ontology l Typical first step: –What are the classes? –What are their attributes?

Attributes and Values l Classes have attributes –Attribute is the TYPE of information »(kind of like a data type in a programming language) –Attributes have VALUES that fit their TYPE »attribute TYPE: integer, VALUE: 9 »attribute TYPE: suit, VALUE: club, heart, spade, diamond »attribute TYPE: name, VALUE: Juanita, Dekai, Laura

Attributes vs. Classes l How do we make this distinction? l Say we are clothing manufacturers. –Fur is a class –Animal is an attribute l Say we are naturalists. –Animal is a class –Fur is an attribute l This example shows that one user’s classes are another user’s attributes

Let’s Design a Cookbook l What are the categories and attributes? l How should we organize them for the: –Table of contents –Index

Next Time l Facets vs. Hierarchies l Psychology of Category Structure