Tom Gruber is an innovator in technologies that extend human intelligence. Building on early work in computer-mediated learning and artificial intelligence, he focuses on creating environments for collective intelligence.
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)