A very good introduction to ontologies: Introduction to Biomedical Ontologies.
This introduction neatly frames the issue addressed by both controlled vocabularies (ontologies) and topic maps.
When faced with multiple terms for a single subject, a controlled vocabulary (ontology), solves the problem by using a single term.
Other terms that mean the same subject are “near synonyms.”
Watch the video and then check back here for a post called: Near Synonyms.
I will discuss how the treatment of “near synonyms” differs between topic maps and controlled vocabularies (ontologies).