Controlled vocabularies comprise simple term lists, synonym rings (search thesauri), authority files, taxonomies, and thesauri. Knowledge organization systems comprise all of these, plus categorization schemes, classiﬁcation schemes, dictionaries, gazetteers, glossaries, ontologies, semantic networks, subject heading schemes, and terminologies. As such, knowledge organization systems can be considered to be broader than controlled vocabularies, including all kinds of controlled vocabularies and more.
Yet, it’s not simply a matter of more types that distinguish knowledge organization systems. Knowledge organization systems include “schemes” that go beyond how the terms are organized and related to each other. Categorization schemes, classification schemes, semantic networks, ontologies present not only terms and relationships but also models of how information/knowledge can be managed and organized. These typically involve additional specifications and documentation on how they are to be used. There is indeed something to the name “knowledge organization system.” A “system” is more than just terms and their relationships.
As such, there is more discourse around knowledge organization systems than controlled vocabularies, per se (separate from discussions specifically about taxonomies or thesauri). Conference sessions of the Association for Information Science & Technology (ASIS&T) more often have “knowledge organization systems” in their titles than “controlled vocabularies.” There is even a professional association dedicated to knowledge organization systems, the International Society for Knowledge Organization (ISKO). There is no comparable organization for controlled vocabularies or just taxonomies or thesauri. ISKO holds conferences with sessions around the various issues of knowledge organization systems, including taxonomies. Recognizing that taxonomies are an important kind of knowledge organization system, the ISKO UK chapter co-sponsors the Taxonomy Boot Camp London conference
Taxonomies are not only included within knowledge organization systems, but they are also a part of the field of knowledge management. As a consultant, I worked with clients who managed taxonomies within their knowledge management services, headed by a manager or director of knowledge management. Also, at a consultancy where I previously worked, taxonomy consulting was part of the larger knowledge management consulting practice
I used to describe taxonomies as only a kind of controlled vocabulary, but now I will start referring to them as knowledge organization systems as well.