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)
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P. Cimiano, and J. Völker. Proceedings of the International Conference on Recent Advances in Natural Language Processing (RANLP), page 166-172. Borovets, Bulgaria, INCOMA Ltd., (September 2005)
V. Tresp, M. Bundschus, A. Rettinger, and Y. Huang. Uncertainty Reasoning for the Semantic Web I, volume 5327 of Lecture Notes in Artificial Intelligence, Springer, Berlin, (2008)
J. Tang, H. fung Leung, Q. Luo, D. Chen, and J. Gong. IJCAI'09: Proceedings of the 21st international jont conference on Artifical intelligence, page 2089--2094. San Francisco, CA, USA, Morgan Kaufmann Publishers Inc., (2009)
J. Tang, H. fung Leung, Q. Luo, D. Chen, and J. Gong. IJCAI'09: Proceedings of the 21st international jont conference on Artifical intelligence, page 2089--2094. San Francisco, CA, USA, Morgan Kaufmann Publishers Inc., (2009)