Subject: Re: GPL & interfaces
From: Ian Lance Taylor <ian@airs.com>
Date: 1 Nov 1999 23:09:22 -0500

   From: Stephen Turnbull <turnbull@sk.tsukuba.ac.jp>
   Date: Mon, 18 Oct 1999 18:28:32 +0900 (JST)

       shapj> First, the meaning of "derived work" is a technical term
       shapj> defined in the legal community with a fair degree of
       shapj> precision.  It means a work of authorship incorporating
       shapj> more than a certain specifically-defined minimum amount of
       shapj> content from some other work of authorship.

   Hm.  I got the impression that "derived work" was actually defined
   differently for the LGPL as compared to the GPL.  Is that true, or
   does the LGPL have to explicitly exempt certain derived works?

Neither the GPL nor the LGPL define ``derived work.''  The LGPL could
be described as exempting certain derived works, but that's not really
what it does: like the GPL, it permits the distribution of a derived
work without source, provided certain specified conditions are met.
The difference between the GPL and the LGPL is not in the definition
of ``derived work,'' but rather in the conditions which must be met
when distributing a derived work without source.

   How is the scope of the derived work defined, if not by the license
   itself?  By this I mean is the "function call -> part of the work, run
   a subprocess -> not part of the work" criterion generally accepted?  I
   always got the impression that was decided by the FSF, but that's
   because the only person I know of who reliably asks a lawyer when he
   doesn't know is Richard Stallman.

In principle, the meaning of ``derived work'' is defined by a court of
law.  This has more or less been done for types of information that
have been around for a long time, such as books or music.  So far as I
know, it has not been done for software.

I think the distinction you mention is generally accepted in the
community, which means that a court would probably accept it too, but
I don't know that it has ever been decided in a court case or written
into a law.

Eventually, the courts will determine exactly what a derived work is
in the case of software, or Congress will write a law defining it, and
then we will know for sure what a copyright-based license like the GPL
can prohibit.  Until then, we just have to go with our best guess.
(This all applies to the U.S. only--I have no idea what the rules are
in other countries.)

Ian