Hi Ross. The ZPL is a brief and concise license. It is clear on providing attribution of authors and copyright. The other requirements it imposes are fairly minimal. Other than this, it permits the code to be used in virtually any manner. The components in the Zope repository upon which Zope and Plone depend upon are licensed this way. It is roughly equivalent to BSD or MIT license. These are liberal licenses and in wide use. TurboGears, Twisted, Zope, and Django all use similar licensing.

The rationale for these liberal licenses is more or less that the use of the licensed code does not impact code using it (other than for the user of the code to include the license in the source and perhaps identify last date of change in mixed sources). This means that not all code or derivatives using the licensed code need be disclosed but when it is offered it must contain the licensing in the source. Mixing code that GPL with nonGPL code on the other hand generally in a derivative that is GPL almost without exception. The requirements and disclosures required by derivative code is detailed in the GPL.

In any case, licensing is a thorny issue. No one really wishes to debate it since it often digresses into heated and divisive exchanges on moral, social or commercial benefit or consequence. That said, it remains a necessary consideration for developers and businesses in relation to their intellectual assets (and also the responsibility one assumes when working with open source).

In relation to Chris's post, my understanding of the Zope repository is that a committer is required to sign an agreement with Zope Corp or ZF. This requires the code to be licensed as ZPL with 50% of intellectual rights to Zope Corp or ZF. Hope this helps.

Regards,
David

Ross Patterson wrote:
Recently, someone wrote to me regarding one of my z3c packages which is
licensed under the GPL.  They asked me to license them under the ZPL
saying that the ZPL would allow the widest range of use for those
packages.  They also implied that using the GPL impacted the licensing
of other code that uses mine.

Mostly this is just a debate I've never taken up before.  I've always
just chosen the GPL because it's the most aligned with my values and
ideals on a "visceral" level.  IOW, it's a gut choice not an educated
choice.

I realize this is an old debate.  I found some lengthy threads on
zope-dev from 2001, but I think there have been some license changes
since then.  I also read the following blog posts:

http://radio.weblogs.com/0116506/2005/11/21.html#a370
http://awkly.org/2005/11/21/gpl-considered-harmful/

Unfortunately, the comment by Chris McDonough mentioned in the latter
doesn't seem to be accessible any more.  I'd love to read it.

From those blog posts, I don't really see any corroboration of the
claims of the person who made the request that I switch to the ZPL.
What exactly about the GPL narrows the range of developers who can use
my code?  What about the GPL impacts the license of other code that
depends on my code?

Here's what I want.  I want anyone who modifies or forks my code to make
their modifications just as accessible to myself and the community as my
code is in the first place.  I also want anyone who forks my code to
credit me and other contributors as authors of the code they forked.  I
have a slight preference to allow proprietary code to depend on my code
without having to open source their code.  I definitely want commercial
entities to be allowed to sell products and services that include my
code as long as credit is given to the authors.

That's just what I want from my admittedly naive perspective.  I'd
like to hear comments on why others think I should or shouldn't want
any of those things from a license.  I'd also like to hear how others
think the license available relate to what I want from a license.

Thoughts?  Is there documentation somewhere about choosing a license?
Maybe a howto I missed in my googling?

Ross

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