Semantic Relations New

Homonymy vs. Polysemy

It could be argued for many NLP applications that a coarse differentiation between the different meanings associated with a single lexical form is adequate to establish a basic interpretation which can guide subsequent processing. This might be the case for some MT systems or NLU systems which only need to establish the general context of discourse. This coarse differentiation might be at the level of homonyms, leaving polysemous words to be associated with an underspecified lexical semantics which is never made fully precise. So what is the homonymy-polysemy distinction and on what grounds is it made? I will show that the distinction is not clear and therefore not a useful basis for deciding what words/senses to include in the lexicon.

A word with (at least) two entirely distinct meanings yet sharing a lexical form is said to be homonymous (e.g. mogul, an emperor, or mogul, a bump on a ski piste), while a word with several related senses is said to be polysemous (e.g. mouth, an organ of the body, the entrance of a cave, etc.) lyons:77. While these definitions are intuitively clear, it has been pointed out many times in the literature on lexical semantics that a clear operational distinction between homonymy and polysemy is lacking. I will review some of the criticisms below, but will begin by introducing an example which emphasises the difficulties of establishing criteria for distinguishing between homonymy and polysemy.

One of the most commonly cited examples of a homonymous word is bank, which has a financial institution sense and a edge of a river sense. These senses seem clearly unrelated, and the fact that they are associated with the same word form seems purely accidental. However, historical linguistics research on Italian has revealed that at some point in the development of the Italian language, these two senses of bank actually coincided by virtue of the fact that bankers (lenders of money) sat on the riverbanks while doing their business. So going to the financial institution meant going to the edge of the river, hence to the bank. Thus a connection between the two modern senses of bank can be established. The relationship between these two senses should presumably not be considered strong enough to establish a relation between them, and therefore to consider bank polysemous rather than homonymous, but what criteria for polysemy do they violate? On what criteria do we decide that senses are related?

Synonymy (equivalence relation)

Synonymy is a kind of semantic relation. Two words (or phrases) are synonyms when they have the same meaning. (Terms with subtle differences between meanings are termed near-synonyms).

Example. The WordNet database differentiates two meanings of the word “computer”. The first meaning is “a machine for performing calculations automatically”. For this meaning is on January 2004 listed the following six synonyms:

• computer,

• computing machine,

• computing device,

• data processor,

• electronic computer and

• information processing system.

Lyons (1995, p. 61) defines two expressions as full synonymous if the following conditions are met:

• All their meanings are identical

• They are synonyms in all contexts

• They are semantic equivalent in all aspects of their meaning

Webster's new dictionary of synonyms discuss the concept at length (p. 5-31) and provide the following definition:

“A synonym, in this dictionary, will always mean one of two or more words in the English language which have the same or very nearly the same essential meaning... Synonyms, therefore, are only such words as may be defined wholly, or almost wholly, in the same terms. Usually they are distinguished from one another by an added implication or connotation, or they may differ in their idiomatic use or in their application.” (Merriam-Webster, 1984, p. 24).

In reality are words seldom or never full synonyms. In WordNet the following definition is given:

“synonymy, synonymity, synonymousness -: the semantic relation that holds between two words that can (in a given context) express the same meaning”. The condition: in a given context is an important reservation.

In Library and Information Science (LIS) are synonyms important because users often use different terms compared with document authors to refer to the same concept. (And different document authors often use different terms, while users may errornously believe they have found the "right" term when they have found only one out of many synonyms). For this simple reason is information retrieval affected by the 'term mismatch' problem. The term mismatch problem does not only have the effect of hindering the retrieval of relevant documents in Boolean sets, it also produces bad rankings of relevant documents in techniques based on partial match.

This problem is dealt with in all forms of controlled vocabulary, thesauri and classification systems. In thesauri this relation is indicated by the USE and USED FOR coding.

In information retrieval are synonyms the terms that are connected with the Boolean operator “OR” in a given query. Such a query may be modified interactively as a result of the user’s evaluation of recall and precision: If recall is too low more synonyms may be added; if precision is too low, some synonyms may be removed (both things can be done because some words regarded as synonyms may provide too much noise while others may improve recall in a qualitative better way). This use of words demonstrates that synonymity should be considered a dynamic and situational relation.

Bibliometrics may be relevant to determine if two expressions should be regarded as synonyms. If they are cited by different groups of researchers with no overlap, this is a strong indication