The Ontology Problem is a fundamental challenge of the emerging Semantic Web. This problem is comprised of three key sub-problems, the Upper Ontology Problem, the Domain Ontology Problem, and the Ontology Integration Problem.
S. Jeschke, M. Wilke, N. Natho, и O. Pfeiffer. Hawaii International Conference on System Sciences, Proceedings of the 41st Annual, стр. 330-330. (2008)