Re: License question

Tom Lane wrote:

>Jeff Davis <jdavis-pgsql(at)empires(dot)org> writes:
>
>
>>Also, can you license code at all if it isn't yours? I would assume you
>>would have to make changes and license the changes you made, and
>>distribute it along with the postgresql-licensed code.
>>
>>
>
>You can't relicense code you don't own
>
Sure you can.

> (if Shachar thinks differently
>I suggest he talk to a lawyer).
>
I have. And one who specializes in free software licenses, at that.

Let's give an example which is simpler, and therefor may make the case a
little clearer. Supposed you painted a picture and give out electronic
versions of it (you have the copyright). You allow everyone to
redistribute the picture, so long as the general tone of the background
color remains blue (license, pretty permissive).

Now let's suppose I take your picture and make several modifications on
it, but none that violates your license (i.e. - the background is still
blueish). Both of us have copyright over the new work, but I may only
distribute it under a license that makes sure that the restrictions I
received it under are met. This means I cannot public domain the
picture. If I do, I am violating your copyright over the picture, as I
can no longer guarentee that the background remains blue. In that sense,
I cannot "relicense" the picture. This is the case even if my public
domain copies still have a blue background, as I have now given people
permission to change a work of art for which you hold a copyright,
outside of the permission you have given either them or me.

One obvious solution is to redistribute it under the original license -
do whatever you like with it, so long as the background remains blue.
That is, however, not the only one. I can also change the license to
whatever I want, so long as I can assure you that your original
requirements are met with any work derived from the new license. For
example, it is perfectly ok to say "you can redistribute this picture,
but you are not allowed to change anything about the color scheme". The
new requirement encapsulates the original requirement, and your license
is therefor not violated. I have, in fact, relicensed your work.

This applies even if I did not make any change to your original work at
all. So long as I can show that all terms of your original license are
met if people follow my new license, you have no quarrel with me. You
requested that people don't change the background color theme. They
can't if they can't change the color theme at all.

Now, obviously, if people can get a picture to me under a certain
restrictive license, and they can get the exact same picture from you
under a more permissive license, they are unlikely to get the picture
from me. That is, however, market forces, not copyright licensing.

If you accept that, just replace "blue" with "free".

>(at least, not from the BSD side --- see below).
>
>When working with GPL or LGPL base code you are constrained to use the
>same license as the base. You still own your own work, but you can't
>redistribute the combined work unless you use the same license.
>
>I don't think you could reasonably choose GPL as the license for your
>mods/additions, since by my reading of the GPL it would forbid you from
>redistributing a combined work that's not all GPL.
>
But the (new, not old) BSD license is "GPL compatible", which means that
I can relicense your work released under the 3 clause BSD as GPL. The
original 4 clause BSD is not GPL compatible, which means I cannot.
Comparing restrictions, and whether license X can guarentee that all the
restrictions imposed by license Y are still met, is what stands at the
core of saying "license X is compatible with license Y".

> But you could choose
>LGPL, or any of the other standard free licenses.
>
>
Hmm, not really. As I'm talking about putting code from PostgreSQL into
the OLE DB provider proper, the linking clause of the LGPL does not
cover this. Let's make it clear - as the LGPL code is all mine, noone
can do or say anything to me if I mix it with non-relicensed BSD code. I
am not violating the BSD license, because it's still BSD, and the person
doing the LGPL license violation is me, the copyright holder, so noone
can have any qualm with this (it's the copyright holder that has to sue,
and I won't sue myself). Doing this does mean that noone except me can
touch this project without removing the BSD code (or relicensing, but
I'm assuming here I accept your claim that I cannot relicense), except
me. Creating free software with conflicting licenses code is legal but
highly recommended against.

> regards, tom lane
>
>
Shachar

--
Shachar Shemesh
Lingnu Open Source Consulting
http://www.lingnu.com/