Note that whilst the taxonomy / ontology is copyrightable by ADA v. Delta
Dental [1], uses of the terms is not so covered (see sec. 12):
"Section 102(b) precludes the ADA from suing, for copyright infringement, a
dentist whose office files record treatments using the Code's nomenclature.
No field of practice has been or can be monopolized, given this constraint.
Section 102(b) permits Delta Dental to disseminate forms inviting dentists
to use the ADA's Code when submitting bills to insurers. But it does not
permit Delta to copy the Code itself, or make and distribute a derivative
work based on the Code, any more than Baker could copy Selden's book."
Section 102 refers to 17 USC 102 [2] ; Baker and Selden were the parties
in the case described in [3] (history of the case written by Pamela
Samuelson).
[1] http://www.law.cornell.edu/copyright/cases/126_F3d_977.htm
[2] http://www.law.cornell.edu/uscode/text/17/102
[3] http://papers.ssrn.com/sol3/papers.cfm?abstract_id=743545