Thesauruses in IT
In Information Science, Library Science, and Information Technology, specialized thesauruses are designed for information retrieval. They are a type of controlled vocabulary, for indexing or tagging purposes. Such a thesaurus can be used as the basis of an index for online material. The Art and Architecture Thesaurus, for example, is used to index the Canadian Information retrieval thesauruses are formally organized so that existing relationships between concepts are made clear. As a result, they are more complex than simpler controled vocabularies such as authority lists and synonym rings. Each term is placed in context, allowing a user to distinguish between "bureau"/"buro" the office and "bureau"/"buro" the furniture. Following international standards, they are generally arranged hierarchically by themes, topics or facets. Unlike a literary thesaurus, these specialized thesauruses typically focus on one discipline, subject or field of study.
In information technology, a thesaurus represents a database or list of semantically orthogonal topical search keys. In the field of Artificial Intelligence, a thesaurus may sometimes be referred to as an ontology.
Thesauruses for information retrieval are typically constructed by information specialists, and have their own unique vocabulary defining different kinds of terms and relationships:
Terms are the basic semantic units for conveying concepts. They are usually single-word nouns, since nouns are the most concrete part of speech. Verbs can be converted to nouns – "cleans" to "cleaning", "reads" to "reading", and so on. Adjectives and adverbs, however, seldom convey any meaning useful for indexing. When a term is ambiguous, a “scope note” can be added to ensure consistency, and give direction on how to interpret the term. Not every term needs a scope note, but their presence is of considerable help in using a thesaurus correctly and reaching a correct understanding of the given field of knowledge.
"Term relationships" are links between terms. These relationships can be divided into three types: hierarchical, equivalency or associative.
- Hierarchical relationships are used to indicate terms which are narrower and broader in scope. A "Broader Term" (BT) or hyperonym is a more general term, e.g. “Apparatus” is a generalization of “Computers”. Reciprocally, a Narrower Term (NT) or hyponym is a more specific term, e.g. “Digital Computer” is a specialization of “Computer”. BT and NT are reciprocals; a broader term necessarily implies at least one other term which is narrower. BT and NT are used to indicate class relationships, as well as part-whole relationships (meronyms and holonyms).
- The equivalency relationship is used primarily to connect synonyms and near-synonyms. Use (USE) and Used For (UF) indicators are used when an authorized term is to be used for another, unauthorized, term; for example, the entry for the authorized term "Frequency" could have the indicator "UF Pitch". Reciprocally, the entry for the unauthorized term "Pitch" would have the indicator "USE Frequency". Unauthorized terms are often called "entry vocabulary", "entry points", "lead-in terms", or "non-preferred terms", pointing to the authorized term (also referred to as the Preferred Term or Descriptor) that has been chosen to stand for the concept. As such, their presence in text can be used by automated indexing software to suggest the Preferred Term being used as an Indexing Term.
- Associative relationships are used to connect two related terms whose relationship is neither hierarchical nor equivalent. This relationship is described by the indicator "Related Term" (RT). Associative relationships should be applied with caution, since excessive use of RTs will reduce specificity in searches. Consider the following: if the typical user is searching with term "A", would they also want resources tagged with term "B"? If the answer is no, then an associative relationship should not be established.
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