linking BSD and GPL code via a plugin

[John Cowan]

Kevin Hunter scripsit:

> I'm confused (yet again!) about linking to libraries and other programs.
> I am working with a BSD licensed project, and I've been tasked to
> write a plugin to call functions of a GPL project.

The FSF claims that such a plugin is a derivative work of the GPLed
code, unless there is a non-GPLed version (separate implementation or
differently licensed copy) that is plug-compatible with the GPLed code.
Thus code written to use readline does not have to be under the GPL, given
that it can work just as well with the equivalent BSD library editline.

Whether there is legal warrant for this claim is more than doubtful, as
ordinary copyrighted works such as books do not normally "interoperate" in
this way.  One hypothetical would be this: given a book like a textbook
that asks questions of the reader, is another independently written
book that answers those questions a derivative work of the first book?
I know of no cases on point.

In any case, it's not about who distributes what, it's about whether and
when one piece of code is a derivative of another when it contains none
of the other.  Clearly in some cases a derivative work is formed: if you
translate an Albanian novel into French, the French work is derivative
of the Albanian work even though it contains no words from the original.
In other cases, it's quite different: we can both draw the Eiffel Tower,
or even photograph it, and neither work infringes the other no matter
how closely similar they are, provided there was no intent to make a copy.

Sorry not to be more definite, but the state of the law is not definite.

-- 
John Cowan            http://www.ccil.org/~cowan     cowan at ccil.org
Uneasy lies the head that wears the Editor's hat! --Eddie Foirbeis Climo