This document is a RDDL/XHTML description of a taxonomy for classifying UDDI entries as rddlSpec, rddlNature, or rddlPurpose. These are the only three valid keyValues, but due to the extra effort to have the UDDI Business Registry (UBR) actually check the validity of keyValues, in UBR it is an "unchecked" taxonomy.
In private UDDI registries, it can be handled as a "checked" taxonomy. UDDI servers often provide a way to upload a taxonomy to their server, which then makes it available through a browser GUI (e.g., to search for things using the keyValues specified by the taxonomy).
The URL of this document (in www-archive) should also appear in the value of the overviewURL in the UDDI tModel for this taxonomy. I first talked about this idea here. Note that I have since expanded the taxonomy from a single keyValue value (rddlSpec) by adding two more. rddlNature is intended to be used for UDDI tModels (in their categoryBag) to classify them as rddlNature; that is, the overviewURL of such tModels can be used as the value of a rddl:nature attribute in RDDL documents. This allows UDDI to be used as a registry for rddl:nature. By doing a find_tModel to a UDDI registry and specifying a categoryBag with keyValue="rddlNature" (using the tModelkey for the RDDL taxonomy tModel) you should be able to find all registered rddl:nature's. Likewise for rddl:purpose by using keyValue="rddlPurpose".