Creative Commons

founded on the notion that some people may not want to exercise all of the intellectual property rights the law affords them (works are automatically copyrighted)

define a set of human and machine readable (RDF/XML) public licenses

Attribution Attribution.
Noncommercial Non-commercial.
No Derivative Works No Derivative Works.
Copyleft Copyleft.

define a means for describing works (Dublin Core and Creative Commons) in RDF/XML and associating licenses

e.g. cc:License, cc:license