K. Siorpaes and M. Hepp, myOntology: The Marriage of Collective Intelligence and Ontology Engineering, in Proceedings of the Workshop Bridging the Gap between Semantic Web and Web 2.0 at the ESWC 2007. LNCS Springer: Innsbruck, Austria, June 7, 2007.
Gruber said he saw four different ways of adding meta-tags to material, ranging from the loosest to the most strict:
1.Folksonomy (informal, user-defined)
2.Controlled vocabularies (the user must deploy a set of defined terms)
3.Taxonomy (Pre-defined terms in which specific terms are subsets of more general terms)
4.Ontology (A rich set of relationships is mapped out among all the terms)