Derivatives of dual-licensed Creative Commons Attribution-ShareAlike and GFDL works
evan at wikitravel.org
Tue May 3 09:15:39 EDT 2005
Hi. This mail is specifically for Dave "Novalis" Turner, who is quoted
on this Wiki web page.
Please read this email carefully; it covers some fine details of
complicated licensing issues.
You state, in the email quoted above, that it's possible to
dual-license a derivative work of a dual-licensed GFDL and Creative
Commons Attribution-ShareAlike (by-say) work. I think you're wrong. I
don't think you looked at the problem carefully enough, nor do I think
you considered the special, exceptionally strong copyleft of these two
licenses. Here's my reasoning:
Section 4 of the GFDL says:
You may copy and distribute a Modified Version of the Document
[...], provided that you release the Modified Version under
precisely this License
Contrast this to section 2a of the GPL:
You must cause any work that you distribute or publish, that in
whole or in part contains or is derived from the Program or any
part thereof, to be licensed as a whole at no charge to all third
parties under the terms of this License.
The GPL requires that derivative works be available under the GPL; the
GFDL requires that derivative works be available under _precisely_ the
GFDL. The first seems to be amenable to multi-licensed derivatives
(e.g., MPL and GPL), while the second does not.
The Creative Commons ShareAlike license element is even more clear:
You may distribute, publicly display, publicly perform, or
publicly digitally perform a Derivative Work only under the terms
of this License [...]
"Only" and "precisely" don't seem to allow multiply-licensed
derivative works. A derivative of a dual-licensed work can be, I
believe, available under one or the other but not both.
So, my questions:
1) Does "precisely this License" in the GFDL mean "only this license,
to the exclusion of all others"?
2) If it does, does this preclude dual-licensing derivative works of
GFDL-licensed works, even if the original work is dual licensed? Why
or why not?
3) (Optional) What about "only under the terms of this License" in the
ShareAlike element? Does this preclude dual-licensing derivative works
of Attribution-ShareAlike-licensed works, even if the original work is
4) Is it possible for copyright holders to add a special exception
allowing dual-licensed derivative works of dual-licensed GFDL and CC
by-sa works? If so, any suggested wording?
Thanks for your time,
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