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)
F. Limpens, F. Gandon, and M. Buffa. Automated Software Engineering - Workshops, 2008. ASE Workshops 2008. 23rd IEEE/ACM International Conference on, (September 2008)
C. Damme, T. Coenen, and E. Vandijck. Scalable Computing: Practice and Experience - Scientific International Journal for Parallel and Distributed Computing, 9 (4):
293-301(December 2008)
F. Limpens, F. Gandon, and M. Buffa. Automated Software Engineering - Workshops, 2008. ASE Workshops 2008. 23rd IEEE/ACM International Conference on, (September 2008)