Re: License question

Tom Lane wrote:

>Jeff Davis <jdavis-pgsql@empires.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/