Re: GPL question

[David Kastrup]

richard@cogsci.ed.ac.uk (Richard Tobin) writes:

> In article <85zm453gjn.fsf@lola.goethe.zz>, David Kastrup  <dak@gnu.org> 
> wrote:
>
>>Defined interfaces are not usually considered to create copyrightable
>>entities as long as they don't contain sufficient creative content by
>>themselves.
>
> This is interesting, because as I understand it the FSF claims that if
> I distribute code that only works with their libraries (because I use
> their interfaces), then I must distribute my code under the GPL even
> if I don't distribute their libraries.

Here is the theory behind that: if the purpose of the code is to be an
example of code, the use of a specific API is no problem.  For
example, if you publish a book with code using this API.

What _is_ restricted is the distribution of a binary that links the
different codes: that is no longer a "mere aggregation" or an
independent work.  It is derivative work.

So you say: "Big deal, I won't link it then.  The customer has to do
it".  Now if the only conceivable use of the software _is_ to link it
to a free version of the software, the linking is an integral part of
the whole activity, and the customer does the linking _on_ _behalf_ of
the software producer, in order to complete the deal.  Since the
customer is acting on behalf of the producer, it does not actually
matter that the producer does not himself do the assembly: he is still
responsible for it.

As soon as there is another conceivable use of the software, the
responsibility for linking the free component moves onto the customer,
and we are talking about aggregation again and not copyrightable
interfaces.

For example, there is a library around that is a drop-in replacement
for the GNU readline library.  Distributing code that can be linked
with either library cannot be used for invoking the "derived work"
clause for the software producer.

In fact, this might likely still be the case if the alternative
library basically just consisted of stubs without functionality,
namely if you could link it in and then got a _functional_ executable
without actual editing functionality, as long as the editing
functionality is not a necessary part of the application.

I don't think that the case "GPLed library distributed under terms of
GPL, but used in a differently licensed product" has been actually
tested in court.  It is likely borderline: the judges might follow
that argumentation, or they might not.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum