Recently I’ve been reading about RDF, which is an attempt by the World Wide Web Consortium to create a standard way of representing information about “resources,” which is the word that they use for things. I’m no fan of XML—a relative of RDF that provides a way to store every type of information in the same horrible HTML-like syntax—and RDF certainly shares its tendency to complicate people’s jobs. But although the broadness of RDF’s goals all but guarantees its unwieldiness, I’m beginning to think that there is a need for a computer-processable way of writing “ontologies” beyond the interoperability concerns that motivated the RDF project.
It’s almost too easy to do the postmodernist critique of totalizing schemes with systems like RDF. The example used in the primer for the OWL 2 Web Ontology Language, a commonly-used extension to RDF, is a system for describing family relationships. Using OWL’s vocabulary for talking about the types of relationships that can hold between things, they define what it is to be a parent, a sibling, and so forth, in statements like this:
EquivalentClasses( :Person :Human )
The authors claim that they do not
intend this example to be representative of the sorts of domains OWL should be used for, or as a canonical example of good modeling with OWL, or a correct representation of the rather complex, shifting, and culturally dependent domain of families. Instead, we intend it to be a rather simple exhibition of various features of OWL.
Sure enough, we get to the zinger a few sections in.
Frequently, the information that two individuals are interconnected by a certain property allows to draw further conclusions about the individuals themselves. In particular, one might infer class memberships. For instance, the statement that B is the wife of A obviously implies that B is a woman while A is a man.
Even when they’re only used as examples, categorization schemes tend to turn into power plays. Think how a person who just married her girlfriend would feel reading that.
But information modeling isn’t all retrograde. There’s an admirable example in Sam Hughes’s very funny essay about how database engineers will have to adapt to gay marriage. And there is more to RDF than what I would Heideggerianly call ontics—the description of categories and subcategories of things.
One type of program that people have developed for RDF is the inference engine, which attempts to mimic human reasoning by drawing conclusions from the knowledge represented in files. Whether or not they will lead to a serious AI, people have put these tools to use straightaway for a quite different purpose, that of checking the consistency of their work while putting ontologies together. This is a different application of the technology from that of defining standard vocabularies to enable different software systems to work together, which is where RDF has found the most application (and which is admittedly very important). It has less to do with the finished product (the ontology file) than with what we learn in the process of writing it, and with the input that the computer is able to give to the writer as revision proceeds.