Mixing licenses

Donovan Hawkins hawkins at cephira.com
Tue Apr 21 18:30:07 UTC 2009

On Tue, 21 Apr 2009, Vlad Stanimir wrote:

> Now lets say that mpeg.exe is 
> licensed under gpl, and i have another plugin wmv.exe with is proprietary 
> licensed. Now mpeg.exe and wmv.exe dont talk to each other  but they both 
> talk to Videoeditor.exe and are both  distributed in the same installer, wil 
> that be a problem with GPL?

>From http://www.fsf.org/licensing/licenses/gpl-faq.html#MereAggregation

"We believe that a proper criterion depends both on the mechanism of 
communication...and the semantics of the communication..."

"...pipes, sockets and command-line arguments are communication 
mechanisms normally used between two separate programs. So when they are 
used for communication, the modules normally are separate programs. But if 
the semantics of the communication are intimate enough, exchanging complex 
internal data structures, that too could be a basis to consider the two 
parts as combined into a larger program."

If your program is invoking mpeg.exe to do the same things that a human 
could do manually then you are on pretty solidly safe ground. Scripting is 
a well established practice and I've never heard anyone claim that a batch 
file must be released under GPL just because it calls a GPL program.

You may even be able to play more intrusive games with an external 
executable (such as poking around in its memory space), though the DMCA in 
the US might apply to some cases. Achieving interoperability by abusing a 
closed source executable is not uncommon, and GPL v3 explicitly exempts 
itself from the DMCA (presumably to ensure that option remains open to 
users trying to work around imposed restrictions).

Where you are more likely to get into trouble is if you built a custom 
version of the GPL program in order to expose functionality that the 
original normally doesn't. If the changes make sense on their own merits 
then you should be fine (especially if they were an improvement that you 
could offer back to the original project), but a court might not look 
favorably if they are merely a tool for you to poke a hole in the GPL 
protection. An example that often comes up is using a Linux kernel driver 
(GPL) to expose functionality to a closed-source user mode program that 
does all the work.

In accounting/tax law they have the concept of "substance over form", 
meaning that what you accomplished matters more than the method by which 
you accomplished it. Of course one man's sham is another man's loophole, 
so it's all theory until a court decides.

Donovan Hawkins, PhD                 "The study of physics will always be
Software Engineer                     safer than biology, for while the
hawkins at cephira.com                   hazards of physics drop off as 1/r^2,
http://www.cephira.com                biological ones grow exponentially."

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