19.2.3 Semantic Fields
So far we've seen the relations of synonymy, antonymy, hypernymy, and hyponymy. Another very common relation is meronymy, the part-whole relation. A leg is part of a chair; a wheel is part of a car. We say that wheel is a meronym of car, and car is a holonym of wheel.
But there is a more general way to think about sense relations and word meaning. Where the relations we've defined so far have been binary relations between two senses, a semantic field is an attempt capture a more integrated, or holistic, relationship among entire sets of words from a single domain. Consider the following set of words extracted from the ATIS corpus:
reservation, flight, travel, buy, price, cost, fare, rates, meal, plane
We could assert individual lexical relations of hyponymy, synonymy, and so on between many of the words in this list. The resulting set of relations does not, however, add up to a complete account of how these words are related. They are clearly all
defined with respect to a coherent chunk of common sense background information concerning air travel. Background knowledge of this kind has been studied under a variety of frameworks and is known variously as a frame (Fillmore, 1985), model (Johnson-Laird, 1983), or script (Schank and Albelson, 1977), and plays a central role in a number of computational frameworks.
We will discuss in Sec. 19.4.5 the FrameNet project (Baker et al., 1998), which is an attempt to provide a robust computational resource for this kind of frame knowledge. In the FrameNet representation, each of the words in the frame is defined with respect to the frame, and shares aspects of meaning with other frame words.
WORDNET
19.3 WORDNET: A DATABASE OF LEXICAL RELATIONS
The most commonly used resource for English sense relations is the WordNet lexical database (Fellbaum, 1998). WordNet consists of three separate databases, one each for nouns and verbs, and a third for adjectives and adverbs; closed class words are not included in WordNet. Each database consists of a set of lemmas, each one annotated with a set of senses. The WordNet 3.0 release has 117,097 nouns, 11,488 verbs, 22,141 adjectives, and 4,601 adverbs. The average noun has 1.23 senses, and the average verb has 2.16 senses. WordNet can be accessed via the web or downloaded and accessed locally.
Parts of a typical lemma entry for the noun and adjective bass are shown in Fig. 19.1. Note that there are 8 senses for the noun and 1 for the adjective, each of which has a gloss (a dictionary-style definition), a list of synonyms for the sense (called a synset), and sometimes also usage examples (as shown for the adjective sense). Unlike dictionaries, WordNet doesn't represent pronunciation, so doesn't distinguish the pronunciation [b ae s] in bass $ ^{4} $, bass $ ^{5} $, and bass $ ^{8} $ from the other senses which have the pronunciation [b ey s].
The set of near-synonyms for a WordNet sense is called a synset (for synonym set); synsets are an important primitive in WordNet. The entry for bass includes synsets like bass $ ^{1} $, deep $ ^{6} $, or bass $ ^{6} $, bass voice $ ^{1} $, basso $ ^{2} $. We can think of a synset as representing a concept of the type we discussed in Ch. 17. Thus instead of representing concepts using logical terms, WordNet represents them as a lists of the word-senses that can be used to express the concept. Here's another synset example:
{chump, fish, fool, gull, mark, patsy, fall guy, sucker, schlemiel, shlemiel, soft touch, mug}
The gloss of this synset describes it as a person who is gullible and easy to take advantage of. Each of the lexical entries included in the synset can, therefore, be used to express this concept. Synsets like this one actually constitute the senses associated with WordNet entries, and hence it is synsets, not wordforms, lemmas or individual senses, that participate in most of the lexical sense relations in WordNet.
Let's turn now to these these lexical sense relations, some of which are illustrated in Figures 19.2 and 19.3. For example the hyponymy relations in WordNet correspond directly to the notion of immediate hyponymy discussed on page 7. Each synset is related to its immediately more general and more specific synsets via direct hypernym
The noun “bass” has 8 senses in WordNet.
1. bass $ ^{1} $ - (the lowest part of the musical range)
2. bass $ ^{2} $, bass part $ ^{1} $ - (the lowest part in polyphonic music)
3. bass $ ^{3} $, bass $ ^{1} $ - (an adult male singer with the lowest voice)
4. sea bass $ ^{1} $, bass $ ^{4} $ - (the lean flesh of a saltwater fish of the family Serranidae)
5. freshwater bass $ ^{1} $, bass $ ^{5} $ - (any of various North American freshwater fish with lean flesh (especially of the genus Micropterus))
6. bass $ ^{6} $, bass voice $ ^{1} $, bass $ ^{2} $ - (the lowest adult male singing voice)
7. bass $ ^{7} $ - (the member with the lowest range of a family of musical instruments)
8. bass $ ^{8} $ - (nontechnical name for any of numerous edible marine and freshwater spiny-finned fishes)
The adjective “bass” has 1 sense in WordNet.
1. bass $ ^{1} $, deep $ ^{6} $ - (having or denoting a low vocal or instrumental range)
"a deep voice"; "a bass voice is lower than a baritone voice";
"a bass clarinet"
| Relation | Also called | Definition | Example |
| --- | --- | --- | --- |
| Hypernym | Superordinate | From concepts to superordinates | breakfast $ ^{{1}} $ $ \rightarrow $ meal $ ^{{1}} $ |
| Hyponym | Subordinate | From concepts to subtypes | meal $ ^{{1}} $ $ \rightarrow $ lunch $ ^{{1}} $ |
| Member Meronym | Has-Member | From groups to their members | faculty $ ^{{2}} $ $ \rightarrow $ professor $ ^{{1}} $ |
| Has-Instance | | From concepts to instances of the concept | composer $ ^{{1}} $ $ \rightarrow $ Bach $ ^{{1}} $ |
| Instance | | From instances to their concepts | Austen $ ^{{1}} $ $ \rightarrow $ author $ ^{{1}} $ |
| Member Holonym | Member-Of | From members to their groups | copilot $ ^{{1}} $ $ \rightarrow $ crew $ ^{{1}} $ |
| Part Meronym | Has-Part | From wholes to parts | table $ ^{{2}} $ $ \rightarrow $ leg $ ^{{3}} $ |
| Part Holonym | Part-Of | From parts to wholes | course $ ^{{7}} $ $ \rightarrow $ meal $ ^{{1}} $ |
| Antonym | | Opposites | leader $ ^{{1}} $ $ \rightarrow $ follower $ ^{{1}} $ |
| Relation | Definition | Example |
| --- | --- | --- |
| Hypernym | From events to superordinate events | $ fly^{{9}} \rightarrow travel^{{5}} $ |
| Troponym | From a verb (event) to a specific manner elaboration of that verb | $ walk^{{1}} \rightarrow stroll^{{1}} $ |
| Entails | From verbs (events) to the verbs (events) they entail | $ snore^{{1}} \rightarrow sleep^{{1}} $ |
| Antonym | Opposites | $ increase^{{1}} \iff decrease^{{1}} $ |
and hyponym relations. These relations can be followed to produce longer chains of more general or more specific synsets. Figure 19.4 shows hypernym chains for bass $ ^{3} $ and bass $ ^{7} $.
In this depiction of hyponymy, successively more general synsets are shown on successive indented lines. The first chain starts from the concept of a human bass singer. Its immediate superordinate is a synset corresponding to the generic concept of a singer. Following this chain leads eventually to concepts such as entertainer and
Sense 3
bass, basso --
(an adult male singer with the lowest voice)
=> singer, vocalist, vocalizer, vocaliser
=> musician, instrumentalist, player
=> performer, performing artist
=> entertainer
=> person, individual, someone...
=> organism, being
=> living thing, animate thing,
=> whole, unit
=> object, physical object
=> physical entity
=> entity
=> causal agent, cause, causal agency
=> physical entity
=> entity
Sense 7
bass --
(the member with the lowest range of a family of
musical instruments)
=> musical instrument, instrument
=> device
=> instrumentality, instrumentation
=> artifact, artefact
=> whole, unit
=> object, physical object
=> physical entity
=> entity
person. The second chain, which starts from musical instrument, has a completely different chain leading eventually to such concepts as musical instrument, device and physical object. Both paths do eventually join at the very abstract synset whole, unit, and then proceed together to entity which is the top (root) of the noun hierarchy (in WordNet this root is generally called the unique beginner).
19.4 EVENT PARTICIPANTS: SEMANTIC ROLES AND SELECTIONAL RESTRICTIONS
An important aspect of lexical meaning has to do with the semantics of events. When we discussed events in Ch. 17, we introduced the importance of predicate-argument
structure for representing an event, and in particular the use of Davidsonian reification of events which let us represent each participant distinct from the event itself. We turn in this section to representing the meaning of these event participants. We introduce two kinds of semantic constraints on the arguments of event predicates: semantic roles and selectional restrictions, starting with a particular model of semantic roles called thematic roles.
(19.19) Sasha broke the window.
(19.20) Pat opened the door.