What is an ontology?

I went to InterOntology 09, at Keio University a week ago. Actually I only attended the first couple of talks and the (free!) banquet; I couldn't make the other talks. Ontology is one of those words I have had trouble grasping, and I attended with no more ambition that understanding what it means.

My ambition was not fulfilled, but I was relieved to know that most attendees were just as confused as me. Okay, relieved is perhaps the wrong word. And by "confused", I don't mean people stood around scratching their heads. I mean people were using it in different ways. Most people who said they were "building ontologies" were actually building databases.

Someone I met there kindly sent me this link:
What are the differences between a vocabulary, a taxonomy, a thesaurus, an ontology, and a meta-model?

This (in conjunction with its first comment) is an excellent article. A bit heavy, but definitely worth the effort.

I feel it backs up the opinion I've been forming that ontology is a word that does not really need to exist. People "building ontologies" are generally data modeling, or taxonomy-building, or semantic-network-building. These terms are more specific, and contain more information about exactly what you are doing.

People using the word ontology may want to emphasize that the grammar allows for validating models using logic. Personally I would rather call that validating the data model, though I do see how a widely used ontology representation language could encourage high quality data validation tools. But they are nowhere near that yet - using SPARQL (pronounced sparkle) appears to be more like writing in assembler than the SQL its name hints at.

On the other hand, if everyone listened to me there would have been no InterOntology conference, and I'd have missed out on a free dinner. Such things need to be taken into consideration. Perhaps I should add "Professional Ontologist" to my business card after all? ;-)