Ray Saintonge wrote:
I checked those links and am not any further ahead. I think that I can understand how thesauri might be relevant; however, I'm puzzled by how they have imported a term from metaphysics to serve their purpose.
I think the term "ontology" entered the scene from artificial intelligence (AI) research, which soaked up some hype from Tim Berners-Lee's "semantic web" ideas. There is a pretty good article at http://en.wikipedia.org/wiki/Ontology_%28computer_science%29 People from information retrieval (IR) or library and information science (LIS) tend to prefer "thesaurus". In some cases people make a difference between the two, but I think they are mostly synonyms or overlapping. WordNet (www.globalwordnet.org and http://www.cogsci.princeton.edu/~wn/) is probably the biggest real-world open-source example.
It is possible to divide the world into people who believe in data structures (those who build WordNet, Dmoz, other thesauri, and the semantic web), and those who believe in free text (those who build Wikipedia and the old non-semantic web). Wikipedia's categories is a border-crossing. Some of the people who could/should contribute might have been turned off by Wikipedia's previous category-free approach.
Sorry for being so vague. I took computer science at a university where information retrieval wasn't even taught.