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What is an Ontology for?

I am sure that everyone who has ever dabbled in the area of Ontology has been asked that question. Personally, I have never heard a truly convincing response; even though I strongly feel that Ontologies are quite important.

I recently listened to a radio segment in which someone in Algeria (I think) was complaining about the new law that required all teaching to be done in Arabic. It seems that most university-level education is in French, and that many parents try to send their kids to schools that teach in French. The issue was that Arabic simply does not have the vocabulary demanded by a modern high-tech education.

Arabic is not alone in this dilemma: French itself is littered with Les mots Anglais; and English is a true hodge-podge of Anglo-Saxon, French, German, Hindu, Japanese, and many other languages. It often happens that when a culture acquires a set of concepts, it does so in the language of the originators of those concepts. It is often considerably easier to import wholesale a set of concepts (a.k.a. an Ontology) than to laboriously map each term into one's own language; often inventing new words just for the sake of it.

So here it is, modern Ontology languages are tools for capturing a collection of concepts that form a coherent whole. With an ontology you can make sense of something, even to the point of making a living at it; without it you are literally lost for words.

What does that mean? When do you know that you have one of these coherent wholes? Is it useful to be coherent?

I think two concepts are important here: closure and prediction.

A set of concepts (a.k.a. paradigm) is coherent when it is closed under the 'idea completion' mapping. This totally new concept refers to what happens when you take an idea and push it a bit. For example, in the world of plumbing, you have copper pipes (and iron pipes), solder, fittings, faucets, etc. etc. The set of plumber's concepts is closed under the transformations implied by the requirements of moving hot and cold water around the house.

The second concept that is important is prediction. In the case of our plumber's jargon, you can be fairly sure that the problems and the tools you encounter in installing central heating will all have a name. The language of plumbing is at least as important to a plumber as is the wrench and the soldered t-connector; because the language frames the problems as well as the solutions to those problems.

Ontology has its own ontology (it's called eating your own dog food). In this case it is possible to ask if an ontology is consistent, open world or closed world, based on OWL or Common Logic (or Prolog). We also need words and more formal tools to capture the notions of closure and predictiveness.

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