The preferred term: use for the descriptor. A term specified by a controlled vocabulary for use in representing a concept in indexing. For example: schools; school uniform; schooling costs; tuition. A preferred term should preferably be a noun or noun phrase.
Preferred lexical labels
The skos:prefLabel property allows a preferred lexical label to be assigned to a resource. Terms used as descriptors in indexing systems will, for example, be represented using this property, as in the following example:
ex:animals rdf:type skos:Concept;
RDF flat literals are formally defined as strings with optional language labels. In this way, SKOS allows a simple form of multilingual labeling. This is done by using the language tag of a lexical tag to restrict its scope to a particular language. The following example illustrates how a concept receives a preferred label in English and a preferred label in French:
ex:animals rdf:type skos:Concept;
Note that the notion of preferred label implies that a resource can only have one such label per language.
Following common practice in KOS design, the preferred label of a concept can also be used to unambiguously represent this concept within a KOS and its applications. Therefore, although not formally mandated by the SKOS data model, it is recommended that no two concepts in the same KOS receive the same preferred lexical label for any linguistic label.
Note the following concepts and definitions:
- Controlled vocabulary: prescribed list of terms or rubrics, each of which has an assigned meaning. Controlled vocabularies are designed for use in classifying or indexing documents and for searching. They typically contain a single preferred term for each concept or entity with links to that term from non-preferred terms. They may also show the relationships between terms.
- The descriptor: use of the preferred term.
- The equivalence relationship: relationship between two terms representing the same concept. When two or more such terms are found in the same monolingual thesaurus, one of them is designated as the preferred term and the other(s) as the non-preferred term(s); the relationship is known as intra-vocabulary equivalence. When both terms are preferred terms in different thesauri, the relationship is known as inter-vocabulary equivalence.
- Indexing. Intellectual analysis of the subject matter of a document to identify the concepts represented in it, and assignment of corresponding preferred terms to enable information retrieval. The term “subject indexing” is often used for this concept, but in a context that does not deal with other elements such as authors or dates, “indexing” suffices.
- Metadata. This is data describing the characteristics of a document. metadata is essentially a catalog record, providing (a) access points by which document records can be classified or retrieved and (b) descriptive information, by which the relevance of a document can be assessed without consulting it in its entirety. Preferred terms or annotations selected during the indexing process are often applied as metadata elements to describe the subject matter of a document.
- The multilingual thesaurus. A thesaurus that uses more than one language, in which each concept is represented by a preferred term in each of the languages, and there is a single structure of hierarchical and associative relationships between concepts that is independent of language.
- The non-descriptor: use the non-preferred term.
- The non-preferred term: use for input term; input term; non-descriptor. A term that is not assigned to documents but is provided as an entry point in a thesaurus or alphabetical index. A non-preferred term is followed by a reference to the appropriate preferred term or terms, e.g., hounds USE dogs.
- Orphan term. This is a preferred term that does not have hierarchical relationships.
- The post-coordinate indexing. This is an indexing system in which the subject of a document is parsed into its constituent concepts by an indexer, but the preferred terms so assigned are not combined until selected by a user at the search stage. Compare this with precocious indexing.
- Pre-combined indexing. This is an indexing system in which the preferred terms assigned to a particular document are syntactically combined into one or more sequences that represent the only combinations available for retrieval. Compare with post-coordinate indexing.
- The string: a sequence of preferred terms representing a compound concept in a precoordinate indexing system.
- The thesaurus. It is a controlled vocabulary in which concepts are represented by preferred terms, formally organized so that paradigmatic relationships between concepts are made explicit, and preferred terms are accompanied by entries of synonyms or quasi-synonyms.
Note: example of precoordinate indexing
When using precoordinated indexing, a bicycle repair manual can be assigned the indexing string consisting of three combined preferred terms.
bicycles – repair – instruction books
This brings together all aspects of bicycle repair in a catalog or searchable list, and might be followed by
bicycles – repair – tools
There would be no direct alphabetical access to this topic under repair, instruction books or tools. This does not mean that individual concepts within a precoordinated string cannot be searched separately, either as controlled preferred terms or as free text, but such methods are not part of the precoordinated indexing system.