I don't know if it's possible to copyright data (if I understand your definition of data correctly), but it should not be, at least, not in the US. A quick skim

I don't know if it's possible to copyright data (if I understand your definition of data correctly), but it should not be, at least, not in the US. A quick skim of the wikipedia article on US copyright law shows that the scope of copyright is meant only to cover the arts and literary and scientific writing. Obviously we know that (unfortunately) that includes software, but data would be a stretch. Also here: http://sciencecommons.org/old/databases/#dbcopyright http://sciencecommons.org/old/databases/#dbcopyright The important quote is: "...whether the data itself is copyrightable, depends on what it is. To the extent it consists of factual information, it will not be copyrightable." If it's not copyrighted, you don't need the GPL or anything similar.