Taxonomies are mapped to each other so that they can be employed in one combination or the other. Mapping was considered to be unidirectional, i.e. from terms in a tagged taxonomy to terms in a retrieval taxonomy. However, with taxonomy mapping being performed more frequently today, the view has become broader as reflected in the emergence of new standards and enhanced features in taxonomy management software.
Simple knowledge organization system (SKOS) and the international standard ISO 25964-2 thesaurus and interoperability with other vocabularies – Part 2 (ISO 25964-2) are two such standards for taxonomy mapping.
SKOS is a world wide web consortium (W3C) standard adopted in 2009 for a controlled vocabulary model and interchangeable format. It specifies not only the familiar thesaurus relationships of broader, narrower, and related, but also what is called mapping relationships comprising of exactMatch, closeMatch, broadMatch, narrowMatch, and relatedMatch.
ISO 25964-2 is substantially about mapping. It defines mapping as the process of establishing relationships between the concepts of one vocabulary and those of another. ISO 25964-2 also covers different kinds of mapping relationships, although it describes more types: equivalence, compound equivalence, hierarchical, associative, exact, inexact, and partial equivalence. It also discusses mapping on the high level between pairs or multiple vocabularies and in what kind of direction/arrangement. The standard also includes examples.
While SKOS provides standardized labels, useful for porting and linking vocabularies between different systems and the web, ISO 25964-2 guides the theory and practice of various types of mappings. Significantly, ISO 25964-2 covers mapping not just between taxonomies, but also between taxonomies and thesauri, thesauri and ontologies, or other controlled vocabularies.
Most commercial taxonomy/thesaurus/ontology management software now support the SKOS standard and the SKOS mapping relationships between vocabularies. Some of the leading vendors additionally include an auto-mapping tool. The tool automatically matches equivalences or near-matches between concepts in two different vocabularies, which can then be manually reviewed and approved or rejected by a qualified taxonomist.
In most of the software that supports taxonomy mapping, the mapping feature is intention and direction agnostic. Therefore, taxonomy owners must plan the mapping exercise in a way that would enable mapping in the direction determined by them. Besides the terms with equivalent meaning, it is also acceptable to map from a narrower to a broader concept as the narrower is an example of the broader and can be used for it. Furthermore, it is equally acceptable to map from a term that is a preferred label to a concept where that term is an alternative label/non-preferred term. In both instances, the mapping would not work in the other direction.
Click here to read the article published by Heather Hedden in her blog The Accidental Taxonomist.
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