From the first time I heard it misused by computer scientists, the term “ontology,” used in their intended sense, has rankled, since it is virtually the opposite of its normal meaning. (And although terms are arbitrary, and their meanings do change, if you’re going to coin a term for “X,” it is a bit perverse to co-opt for it the term that currently means “not-X”!)
Ontology is that branch of philosophy that studies what exists, what there is. (Ontology is not science, which likewise studies what there is; ontology is <i>metaphysics</i>: It studies what goes beyond physics, or what underlies it.)
Some have rejected metaphysics and some have defended it. (In “Appearance and Reality,” <a href=”http://www.elea.org/Bradley/”>Bradley</a> (1897/2002) wrote (of Ayer) that ‘the man who is ready to prove that metaphysics is wholly impossible … is a brother metaphysician with a rival theory.”)
Be that as it may, there is no dispute about the fact that “ontology,” whatever its merits, is distinct from — indeed the complement of — “epistemology,” which is the study of how and what we <i>know</i> about what exists. In fact, one of the most common philosophical errors — a special favorite of undertutored novices and overconfident amateurs dabbling in philosophy — is the tendency to confuse or conflate the ontic with the epistemic, talking about what we do and can <i>know</i> as if it somehow constrained what there is and can <i>be</i> (rather than just what we can know about what there can be).
Well, knowledge engineering’s misappropriation of “ontology” — to denote (in the wiseling words of <a href=”http://en.wikipedia.org/wiki/Ontology_(computer_science)”>Wikipedia</a>) “a ‘<a href=”http://tomgruber.org/writing/ontolingua-kaj-1993.pdf”>formal, explicit specification of a shared conceptualisation</a>’… <a href=”http://www.ontopia.net/topicmaps/materials/tm-vs-thesauri.html#N773″>provid[ing] a shared vocabulary</a>, which can be used to model a domain… that is, the type of objects and/or concepts that exist, and their properties and relations’ — is a paradigmatic example of that very confusion.
What knowledge engineers mean is not ontology at all, but “epistemonomy” (although the credit for the coinage must alas go to <a href=”http://www.informaworld.com/smpp/content~content=a739409602~db=all”>Foucault</a>).