[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:

        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