[erlang-questions] GNU GPL, MIT, BSD and compatibility

[Alpár Jüttner]

> > The GNU GPL does *not* require that the linked software is released (or
> > re-licensed) under the terms of the GNU GPL itself.
> 
> In fact, there there is a paragraph in GNU GPL that seems to define when
> it is not necessary to use GPL in your work using a GPL software:

To be clear, this is a quotation from GNU GPL (v3).

> 
>         A compilation of a covered work with other separate and
>         independent works, which are not by their nature extensions of
>         the covered work, and which are not combined with it such as to
>         form a larger program, in or on a volume of a storage or
>         distribution medium, is called an “aggregate” if the compilation
>         and its resulting copyright are not used to limit the access or
>         legal rights of the compilation's users beyond what the
>         individual works permit. Inclusion of a covered work in an
>         aggregate does not cause this License to apply to the other
>         parts of the aggregate.
> 
> Assume that Erlang is linked against a GPL lib. Is that an aggregation?
> (Then no GPL is necessary) Or it "is combined with it such as to form a
> larger program" (Then Erlang seems to be requested to use GPL)? It is
> far too fuzzy for me.
> 
> > But the copyright law *does* require that the final product (new code +
> > libraries) complies with all the involved software licenses.  And since
> > the GNU GPL (either v2 or v3) prohibits that additional restrictions are
> > placed on resulting software, then the final product cannot be
> > distributed under a proprietary, restrictive license.
> > 
> > If there are no such additional restrictions, then there are no problems
> > at all; and if the final product is composed by GNU GPL-compatible
> > licenses, then there are no such additional restrictions.
> > 
> > Practical example:
> > 
> >       * "libfoo" is GNU GPL'ed;
> >       * program "bar" depends on libfoo;
> >       * therefore, "bar" must be released under *any* GNU GPL-compatible
> >         license --- otherwise the "libfoo+bar" bundle is not legally
> >         usable/distributable at all.
> > 
> > "bar" could thus be released under the terms of the MIT or BSD license.
> > If someone modifies it and removes the "libfoo" dependency, or replaces
> > "libfoo" with a non-GPL'ed version, then the GNU GPL conditions do not
> > apply anymore, and future users of "bar" will be able to make it
> > proprietary, add restrictive licensing terms, etc.
> > 
> > In other words, the GNU GPL is not "viral" (as someone else wrote on
> > this thread), or at least is not any more viral than any other software
> > license.
> > 
> > 
> > > Bottom line:  if you want your code to play well with other open
> > > source project that don't use the GPL, pick something like the
> > > BSD/MIT/MPL.
> > 
> > ...or, in general, choose any GNU GPL-compatible license :-)
> > 
> > Regards,
> > 
> > alceste
> 
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