The equivalence relationship is primarily established between synonymous or quasi-synonymous terms that refer to the same concept. It is the the relationship between a preferred term and its corresponding non-preferred terms.
The relationship should be expressed using the following conventions:
USE, written as a prefix to the “preferred term”, or “descriptor”
UF (use for or used for), written as a prefix to indicate the “non-preferred term” or “non-descriptor”
The function of the relationship is to guide the user to the term that is preferred for both indexing and searching.
The equivalence relationship is often used between terms that are not true synonyms, but whose meaning is sufficiently close to the desired concept that it is convenient to treat them as equivalent. In general, equivalence is established when the terms are synonyms. That is, they have identical or nearly identical meanings and usage in a wide range of contexts. Synonyms can arise because of trade names, popular and local usage or superseded terms etc., and may include:
- names or terms of different linguistic origin.
Example: freedom/ liberty; - dialectical variants.
Example: elevator/ lift - abbreviation, acronyms.
Example: AIDS/auto-immune deficiency syndrome - popular and scientific names.
Example: salt, sodium chloride - common terms and trade names.
Example: petroleum jelly/ Vaseline - current terms / outdated or deprecated terms.
Example: intellectual disability/ mental handicap - standard names and slang or jargon terms.
Example: policeman/ copper - irregular plurals.
Example: foot/feet - lexical variants.
Example: online/ on-line, color/ colour
In these cases, a preferred term should be selected to serve the needs of the majority of users. This rule should be applied consistently throughout the thesaurus. Consistent spelling conventions should also be adopted, and all the editorial conventions and criteria should be noted in an introduction to the thesaurus.
- The terms are quasi-synonyms. Quasi-synonyms, are terms with meanings that are regarded as different, but, for the purpose of retrieval, they are treated as equivalents in the controlled vocabulary.
Example: sea water / salt water). - Representation of complex concepts by a combination of terms. Where a multi-word term is deemed to be unsuitable as a preferred term, but might be sought by some users, it may be represented by a combination of two or more preferred terms (coal mining USE coal AND mining)
The controlled vocabulary’s synonyms or variants associated with each term enable document retrieval even when the words entered by the indexer into a search box do not exactly match any text in the relevant document.
