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Re: do DFSG require that derived works use the original licence?

On Mon, 22 Nov 2010 21:15:52 +0100 Lukas Baxa wrote:

> Hello,


> I went through the Debian Free Software Guidelines (DFSG) and I have
> a question to point number 3 - Derived works - which states:
> # The license must allow modifications and derived works, and must allow
> # them to be distributed under the same terms as the license of the
> # original software.
> If I understand it correctly, it must be allowed by the original licence
> that the license of the derived work is identical (or almost identical).
> But it is not required that the licence remains unchanged, it might be
> different.

Yes, a non-copyleft license may indeed meet the DFSG.

A copyleft license is one that requires derivative works to be available
under the same licensing terms as the original work, and that forbids
the addition of further restrictions.
The canonical example of a free copyleft license is the GNU GPL [1][2],
but there are other copyleft licenses around...

[1] version 2 <http://www.gnu.org/licenses/gpl-2.0.txt>
[2] version 3 <http://www.gnu.org/licenses/gpl-3.0.txt>

A license which does not include such a requirement (and thus has no
copyleft mechanism) is often referred to as a "non-copyleft license".
The most famous examples of free non-copyleft licenses are the BSD
licenses [3], the Expat/MIT license [4], and the zlib license [5]. 

[3] 3-clause variant <http://www.debian.org/misc/bsd.license>
[4] see <http://www.jclark.com/xml/copying.txt>
[5] see <http://www.gzip.org/zlib/zlib_license.html>

> As far as I know, GPL requires it.

Yes, it does, see above.

> But it seems to me that DFSG do not.

They do not, in the sense that having a copyleft mechanism is not
necessary for a license to be considered acceptable according to the
And indeed, as anticipated above, several non-copyleft licenses do meet
the DFSG. There are also a number of copyleft licenses which likewise
meet the DFSG.

> Does it mean that it would be possible to include software in Debian
> that could be derived and licensed otherwise than the original software?

Yes, as long as the software package complies with the DFSG, it can be
included in Debian (main).
And there are indeed many non-copyleft-licensed software packages in
Debian (main), as well as many copyleft-licensed packages.

> And does it mean that such derived software might even be a proprietary
> software?

It means that anyone can take a non-copyleft-licensed software package
out of the Debian (main) distribution, modify it, thus creating a
derivative work, and distribute such derivative work under different
licensing terms than the original ones (as long as the original license
is complied with!), even under proprietary terms.

However, a proprietary derivative work of a non-copyleft-licensed
software package cannot be included back in Debian (main).

Please note that this "proprietarization" process is not allowed by
copyleft licenses (such as the GPL).

I hope this clarifies things a bit.

 Need some pdebuild hook scripts?
..................................................... Francesco Poli .
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