[cc-licenses] Most important feature: GPL-compatibility

Francesco Poli invernomuto at paranoici.org
Fri Dec 30 07:10:33 EST 2011

On Thu, 29 Dec 2011 10:21:48 +0000 Rob Myers wrote:

> On 28/12/11 21:44, Francesco Poli wrote:
> > 
> > In these cases, having parts of the game licensed under the terms of
> > the GNU GPL and parts under the terms of CC-by-sa (or CC-by) may create
> > compatibility issues and/or legal uncertainty, which may significantly
> > slow down the development of the game itself.
> Are there any examples of this happening?

I don't remember specific examples, unfortunately, since I tend to
search for Free games without this kind of issues and forget the ones
that are encumbered...
Anyway, I know of discussions that arise in Free game development
communities about compatibility between CC-licensed game data and
GPL-licensed game engines: those discussion are sometimes very lengthy
and often due to misconceptions about licensing and copyright laws
(hence, legal uncertainty). However, those lengthy discussions are
time-consuming: that time would have been better spent in creating more
and/or higher quality artwork for Free games or in writing more and/or
higher quality code for game engines!  

> Game assets being under an appropriate CC license shouldn't affect game
> engine code licensing.

As long as there's a clear separation between game data and game
engine, yes, you are probably right.

However, some people think that a tight dependency between the engine
and the data might imply that the game should be considered as one
whole work. Depending on how interchangeable the game data are (is the
game engine able to load a generic map in a given format, generic
graphical representations for the game items, or does it expect a map
with specific features, and graphics with precise characteristics?),
this might be false or true. Whenever this is true, a GPL-licensed game
engine implies that each part of the game has to be GPL-compatible, or
otherwise the game will be legally undistributable.

A GPL-compatible CC-by-sa (and CC-by) license would instantly solve all
this legal uncertainty and let people concentrate on game development.

> > How can GPL-compatibility be implemented into CC-v4.0 licenses?
> > 
> > I think the only possible approach is including an explicit one-way
> > conversion clause.
> The MPL 2 beta has been mentioned as an example for how this could work:
> https://mpl.mozilla.org/wp-content/uploads/2011/03/MPL-2-B2-plain.txt

The MPLv2 release candidates have a compatibility clause with other
Secondary Licenses, but this compatibility may be disabled.
This is suboptimal, IMHO.

> >   * CC-by-sa-v4.0 should include an explicit one-way conversion clause
> > that would allow redistribution of the work under the terms of the GNU
> > GPL version 2 or any later version
> The current version of the GPL is 3, so the current CC licenses should
> be compatible with GPL 3.

The GNU GPL v2 is still widely used, even without the "or later" option.
A compatibility with only the GNU GPL v3 or later would not solve all
the GPL interaction headaches...

> MPL 2B2 also explicitly allows compatibility with the LGPL and AGPL. CC
> licences should be directly compatible with the AGPL at least.

I don't consider works licensed under the terms of the GNU AfferoGPL v3
as Free Software, hence I am not pushing for AfferoGPL-compatibility.
But that's another story...

> >   * CC-by-v4.0 should include an explicit one-way conversion clause
> > that would allow redistribution of the work under the terms of the zlib
> > license: http://www.gzip.org/zlib/zlib_license.html
> > 
> > I chose the zlib license, since it's a simple permissive non-copyleft
> > license which is GPL-compatible. Another similar license could be
> > chosen as well, if considered more suitable (for example the Expat
> > license: http://www.jclark.com/xml/copying.txt   or the 3-clause BSD
> > license: http://www.debian.org/misc/bsd.license).
> Why would this be needed? Work under BY and MIT or X11 (for other
> examples) can be used together in derivatives/adaptations without
> conflict.

But CC-by is incompatible with the GNU GPL, as confirmed by the FSF.
Hence, without a conversion clause, GPL-compatibility issues would stay
unfixed for CC-by.
Since CC-by does not want to be a copyleft license, I think the most
appropriate conversion is from CC-by to a permissive non-copyleft (and
GPL-compatible) license, such as the zlib license.

> Unlike copyleft licences, permissive licenses do not have the
> requirement that derivatives be placed under the same license and so
> they do not have the same compatibility problems as conflicting copylefts.

They may have GPL-compatibility issues, just like the 4-clause BSD
license has: I suppose you are familiar with the Obnoxious Advertising
Clause (OAC) issue, aren't you?

 New GnuPG key, see the transition document!
..................................................... Francesco Poli .
 GnuPG key fpr == CA01 1147 9CD2 EFDF FB82  3925 3E1C 27E1 1F69 BFFE
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