Truisms about ontologies

What the heck do you use ontologies for? Clay Shirky says they're overrated and useless for organizing content on the Web. This is quite true, at this time you can't use ontology to organize the entire web. (I will probably do a point-by-point reaction to this article at some point. He gets many things right and a few things half-right in distressing ways.) If you can trust content creators and the web community (which, by the way, you can't) you can build an ontology out of their tags and metadata. It still misses those people who don't understand how to create metadata or who can't be bothered to add it to their pages.

Structured data has several practical uses, and things go totally petwang when you try to mix them without acknowledging or understanding that you're mixing them. Here's how I've used ontologies and taxonomies:

A hierarchical taxonomy allows you to present content in an even, logical distribution for people to browse. This is often not accurate but it is understandable and easy to move through.

It can be used to explain semantic meaning to a computer.

It can hold synonyms and relationships between concepts.

It can describe a particular domain and help surface missing content.

One particular friction I've seen pretty much everywhere I've worked is the clash between the need to organize content and the need to have an accurate ontology. Sometimes you have to create classes and categories that are spurious just to present content in a way that is meaningful to a browser and that does not waste their time with needless clicking. For instance: http://dmoz.org/Arts/Performing_Arts/Acting/Actors_and_Actresses/ The letters at the top act like categories, but don't actually impart meaning to the child categories. You can see what letter the person's name starts with just by looking at it. However, if you throw thousands of categories up on a page, you are going to overwhelm your audience. It doesn't make for accurate ontology, but it makes for a good user interface.