Apache v. GPL

[Seth David Schoen]

W. Yip writes:

> Hi. I have some trouble grasping why Apache license is incompatible with
> the GPL.
> 
> Is it because of the naming restrictions in Apache constituting additional
> restrictions that are prohibited by the GPL? Or is it because of:
> 
> ========
> Redistributions of any form whatsoever must retain the following
>  *    acknowledgment:
>  *    "This product includes software developed by the Apache Group
>  *    for use in the Apache HTTP server project (http://www.apache.org/)."
> ========
> 
> The above sounds like the obnoxious advert clause in the dreaded 'old-BSD'.
> 
> Then again, how does an advertisement clause such as the above amount to
> incompatibility with GPL?

The GPL requires people relying on its permissions to grant the same
permissions to others in order to distribute code.

The GPL gives you permission to distribute with no advertising clause, so
if you distribute with a requirement to retain an advertising clause,
you have not successfully

	cause[d] any work that you distribute or publish, that in
	whole or in part contains or is derived from the Program or any
	part thereof, to be licensed as a whole at no charge to all third
	parties under the terms of this License.

and you may also be in trouble because

	[y]ou may not impose any further restrictions on the recipients'
	exercise of the rights granted herein.

The conventional view on GPL compatibility, which has been disputed
sometimes, is that a license must be strictly less restrictive than
the GPL in every regard, or else allow sublicensing under the GPL,
in order to be GPL-compatible.

I shouldn't say "or else" -- because of the passages quoted above, we
can argue that "strictly less restrictive than the GPL in every
regard" _implies_ allowing sublicensing or dual licensing under the GPL.
And that is what the GPL expects.

> My final question is this. When literature mentions 'compatibility', do
> they refer to compatibility of licenses in a situation involving:
> 
> (i) dual licensing (eg. Perl under both Artistic and GPL); or

It seems unlikely that a license would be successful in the free software
world if it attempted to prohibit dual licensing, so no.

> (ii) intermixing of code released under different licenses.

Yes -- as Jim Dennis said yesterday, "the ability to merge two projects"
into one, or to excerpt code from one project and re-use it in another,
releasing the end result to the public as a free software program.

-- 
Seth David Schoen <schoen at loyalty.org>  | And do not say, I will study when I
Temp.  http://www.loyalty.org/~schoen/  | have leisure; for perhaps you will
down:  http://www.loyalty.org/   (CAF)  | not have leisure.  -- Pirke Avot 2:5