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From Marvin Humphrey <mar...@rectangular.com>
Subject Re: Podling Graduation Rally
Date Tue, 21 Feb 2017 06:49:05 GMT
On Mon, Feb 20, 2017 at 10:47 AM, Mike Jumper <mike.jumper@guac-dev.org> wrote:
> AFAIK, only the copyright holder can relicense a copyrighted work, whereas
> others may sublicense under compatible terms so long as the original
> license grants that permission (ie: the license of the original work is not
> actually changing).
>
> Is that not correct?

Correct, and well said!

When we assert that an Apache release package is available under the
ALv2 even though it bundles BSD-2-clause licensed code (as is the case
with MADlib), we are suggesting that the ALv2 "subsumes" the
BSD-2-clause license -- that fulfilling all the requirements of the
ALv2 suffices to fulfill all the requirements of the BSD-2-clause
license.

This is sometimes called "sublicensing", and it only works in one
direction: a license with more restrictions can subsume one with
fewer, but not the other way around.

In contrast, "relicensing" is usually taken to mean the original
copyright holder granting an *additional* license of any type. For
example, if you're the copyright holder, you can take something which
is available only under a proprietary license and make it available
under an open source license.  Or you could take something available
under the GPL and make it available under the ALv2.

(Of course the difficulty of "relicensing" in the context of open
source is that there may be many copyright holders who need to
participate in a relicensing effort -- and if you can't get them all
on board, you might have to strip out and replace code that couldn't
be relicensed.)

For more information on combining software under multiple open source
licenses, I like this article by Luis Villa:

   https://opensource.com/law/11/9/mpl-20-copyleft-and-license-compatibility

This is outdated but still a good read:

   http://www.catb.org/esr/Licensing-HOWTO.html#compatibility

Marvin Humphrey

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