Nowadays, taxonomy and thesaurus often are used interchangeably. Indeed, we can consider a hierarchical thesaurus (which most are these days) as a fancy taxonomy. In either case, we use the controlled vocabulary for the indexing and retrieval. The hierarchical array is for our convenience for either navigating the collection when we are searching or for organizing the terms.

With a taxonomy, you have the hierarchy. Add related terms, synonyms, and other
stuff as you need them and you have a thesaurus.

I think we know that a hierarchy contains two different kinds of relationships and the other ones are important. At the end of the day, it’s the term equivalents that help you most in search, the related terms that will give you a web of knowledge and it’s the hierarchy that aids in search and browsing.

Taxonomies and thesauri are adjacent on that continuum of vocabulary types, from simple to complex that we’ve discussed before. The continuum starts with flat uncontrolled lists, such as those Saturday lists that we make that are not very complex. Name authority files are not very complex. Synonym rings we can constantly add to. After that, we get into control, taxonomy, thesaurus, ontology, and finally, refining into a semantic network as they grow.

We have the lists, which will be things like authority lists, glossaries, gazetteers, dictionaries. Then we have the classification and categorization systems; then we have things that form relationships. When we get into the thesaurus level, we are into relationship groups. A lot of people are going to start at the categorization and taxonomy and grow into a thesaurus as they add related terms over the years, as you figure out the relationships.

Marjorie M.K. Hlava
President, Access Innovations