There was an interesting discussion at lunch about SKOS and I finally had something click about the taxonomy of terms for ontologies. Yeah, yeah I know, but give me a second… It seems to me that it goes like this:

1. In the beginng was a controlled vocabulary, and it was good, but it was a flat list of terms.

2. A taxonomy is a single controlled vocabulary that contains an explicit hierarchy of terms that are related solely by their relative position in the hierarchy.

3. A thesaurus is composed of one or more controlled vocabularies and the relationship betwen the terms is expressed using a controlled vocabulary of ‘thesaural’ relationship concepts.

4. An ontology is composed of one or more controlled vocablaries and the relationship betwen the terms is expressed using relationship concepts that do not necessarily belong to any specific controlled vocabulary of concepts.

This may not be entirely correct, but it sure helped me make sense of that whole landscape.