DublinCore

Meta data set for attributing documents. http://www.dublincore.org/documents/dces/

RFC 2413 XML namespace http://purl.org/dc/elements/1.0/

This is the prefered namespace to model document meta data. We use other namespaces only for things which don't map to the Dublin Core namespace.

A Guidance on expressing the Dublin Core within the Resource Description Framework (RDF)

Here http://www.dlib.org/dlib/october00/baker/10baker.html is a good explanation.

The Dewey Decimal Classification System http://www.oclc.org/dewey/about/ provides a dynamic structure for the organization of library collections. Beware: use at your own risk! The OCLC claims, that they own the "thing", which is clearly impossible, given that it was invented some 130 years ago. Only modifications made since might be under newer copyright. [Even american understanding of copyright would not extend so far. So we claim HoeheresRecht easily. But: you've been warned, those might sue you, who uses it. (Not me, who just writes what he thinks is true.)]