I am frequently asked to explain some of the more abstract concepts in taxonomy and ontology work. I thought I'd start writing them down as I come up with them. Feel free to comment on their success - I hope some people find them useful!

Deprecation is a very useful technique that is often overlooked. In the context of taxonomies and ontologies it means to stop using an old term in favor of a new one. Rather than simply deleting the old term, creating the new term and then emailing everyone you think cares with a note about the change, you can include it in your model. This is a much more thorough way of ensuring all of the people and applications that use your data have the up-to-date information.

Some examples: search engines can expand their given query to cover both terms; indexers can be given the most recent version to tag with; end users can be notified via an RSS feed of the change.

It's not as strange a technique as you might think. We encounter deprecation regularly. The image to the right shows one example. This is a road sign in Pennsylvania. It used to be that highway exits were numbered sequentially from one end of the highway to the other. Of course, suburban sprawl demanded the addition of off- and on-ramps, and new exit numbers had to be slipped in, leading to signs reading "225a," "225b," "225c" and so forth. Many transportation departments decided to simply renumber all of the exits based on the nearest mile marker, such that exit 37 is within the 37th mile of the highway from it's beginning measurement point. To help ease confusion for the driver and/or navigator, the old exit was noted on the sign post as well as the new. This is deprecation. This sign is saying, "If you want Street Road, take this exit, number 37. You may know it as exit 25, but we changed the number. Please use this new number from now on."

Deprecation - reflect the new, respect the past.