[vtk-developers] Scope of VTK and it's potential as a common research language

Mon Feb 1 09:27:44 EST 2010

>> It would be great then if a BSD like license can be adopted with
>> explicit clauses such as these.. but that's entirely upto the eigen
>> folks.
>
> Yes, that would be nice. In our case, as I explained, such a "BSD +
> preventing proprietary forks" would be equivalent to the LGPL, but
> that would allow us to do without our long FAQ. I could attempt to
> write such a license, but that's not reasonable as I'm not a lawyer.

I believe that there are several licenses that already do this. Take a look
at this page: http://developer.kde.org/documentation/licensing/licenses_summary.html

One that sticks out is the Apple Public License:
http://www.opensource.org/licenses/apsl-2.0.php

-berk

On Mon, Feb 1, 2010 at 8:38 AM, Benoit Jacob <jacob.benoit.1 at gmail.com> wrote:
> 2010/1/31 Karthik Krishnan <karthik.krishnan at kitware.com>:
>> I believe Benoit's already put forth one (and the only ?) concern : to
>> prevent forks of eigen.
>
> Indeed, that's the main reason: we don't want to allow _proprietary_
> forks of eigen. Different open source projects are in different
> situations, allowing them different licenses. Eigen is a
> volunteer-only project, so developer motivation is subtle and is our
> only asset, and Eigen developers have stated that their motivation
> would be affected if our license allowed proprietary forks.
>
>> It would be great then if a BSD like license can be adopted with
>> explicit clauses such as these.. but that's entirely upto the eigen
>> folks.
>
> Yes, that would be nice. In our case, as I explained, such a "BSD +
> preventing proprietary forks" would be equivalent to the LGPL, but
> that would allow us to do without our long FAQ. I could attempt to
> write such a license, but that's not reasonable as I'm not a lawyer.
>
> Benoit
>
>>
>> On Mon, Feb 1, 2010 at 8:24 AM, Andrew Maclean
>> <andrew.amaclean at gmail.com> wrote:
>>> Jacob,
>>>   In an attempt to move along a very interesting discussion, I would
>>> like to get to the point:
>>>
>>>   Would you be happy to use a BSD like license the same as VTK? It
>>> seems to me that this will nicely remove all the complexities raised
>>> in the previous discussion.
>>>
>>> Is there a specific reason for preferring LGPL?
>>>
>>> Regards
>>>   Andrew
>>>
>>>
>>>
>>> On Mon, Feb 1, 2010 at 6:55 AM, Benoit Jacob <jacob.benoit.1 at gmail.com> wrote:
>>>> 2010/1/31 Benoit Jacob <jacob.benoit.1 at gmail.com>:
>>>>> 2010/1/31 Berk Geveci <berk.geveci at kitware.com>:
>>>>>> I don't agree. Here are two sections:
>>>>>>
>>>>>> 0. Additional Definitions.
>>>>>>
>>>>>> ...
>>>>>>
>>>>>> A “Combined Work” is a work produced by combining or linking an
>>>>>> Application with the Library. The particular version of the Library
>>>>>> with which the Combined Work was made is also called the “Linked
>>>>>> Version”.
>>>>>>
>>>>>> ...
>>>>>>
>>>>>> 4. Combined Works.
>>>>>>
>>>>>> You may convey a Combined Work under terms of your choice that, taken
>>>>>> together, effectively do not restrict modification of the portions of
>>>>>> the Library contained in the Combined Work and reverse engineering for
>>>>>> debugging such modifications, if you also do each of the following:
>>>>>>
>>>>>> ...
>>>>>>
>>>>>>
>>>>>> I read these together to conclude that a binary that is compiled from
>>>>>> any code that includes Eigen is "Combined Work" (a work produced by
>>>>>> combining through the inclusion of templates). If that is the case, 4
>>>>>> would apply and hence the reverse engineering clause. It would be
>>>>>> against the spirit of LGPL to grant templated libraries less
>>>>>> protection than compiled libraries so why would they leave such a
>>>>>> loophole?
>>>>>
>>>>> Section 3 only talks about using material from header files. It never
>>>>> says that this material is assumed to be used by #include'ing it.
>>>>>
>>>>> If VTK uses Eigen headers code, and then application X uses VTK, then
>>>>> the only Eigen code that application X uses is code from Eigen's
>>>>> header files. Actually, all Eigen code is located in header files. So
>>>>> Section 3 still fully applies.
>>>>>
>>>>> One might wonder the extent to which that might be used to abuse the
>>>>> LGPL by claiming that arbitrary files are header files. In the case of
>>>>> Eigen, it's very simple: all our internal source file have the ".h"
>>>>> extension and all our documentation tells to use Eigen by #including
>>>>> files, not linking to anything.
>>>>
>>>> ...and perhaps most conclusively, these files are inherently header
>>>> files at the level of their contents, for example, they have include
>>>> guards, and they define templates without instantiating them which
>>>> would be a NOP if they weren't headers.
>>>>
>>>> Benoit
>>>>
>>>>>
>>>>> As to why this "loophole", I believe that's simply because there's no
>>>>> way around it if the FSF wanted the LGPL to be applicable at all to
>>>>> libraries that have nontrivial code in header files, which includes
>>>>> most C++ libraries including Qt (think QVector). The reason why
>>>>> there's no way around it is that #including is in essence similar to
>>>>> static linking, and doesn't have a runtime analogue.
>>>>>
>>>>> Benoit
>>>>>
>>>>>
>>>>>
>>>>>>
>>>>>> Of course, the copyright holders of Eigen are free to write an
>>>>>> addendum to the license that explicitly states (4) does not apply.
>>>>>>
>>>>>> My vote is to keep Eigen out of core VTK. I wouldn't have any problem
>>>>>> with releasing an application that brings together VTK and Eigen (and
>>>>>> Qt for that matter) because I don't see any issues with LGPL's
>>>>>> requirements but I don't think many of VTK's users that develop
>>>>>> proprietary apps would share my opinion. We have worked very hard to
>>>>>> keep VTK's license free of complications and the value Eigen adds is
>>>>>> not worth wasting all of that effort.
>>>>>>
>>>>>> -berk
>>>>>>
>>>>>>
>>>>>> On Sun, Jan 31, 2010 at 11:14 AM, Benoit Jacob <jacob.benoit.1 at gmail.com> wrote:
>>>>>>> 2010/1/31 Berk Geveci <berk.geveci at kitware.com>:
>>>>>>>> Hi Benoit,
>>>>>>>>
>>>>>>>> That's great! The only clause that still gives me pause is the
>>>>>>>> following from section 4:
>>>>>>>
>>>>>>> Section 4 doesn't apply at all to Eigen ;) see my previous e-mail.
>>>>>>>
>>>>>>> So if this is your only concern then I am very optimistic :)
>>>>>>>
>>>>>>> Benoit
>>>>>>>
>>>>>>>>
>>>>>>>> "You may convey a Combined Work under terms of your choice that, taken
>>>>>>>> together, effectively do not restrict modification of the portions of
>>>>>>>> the Library contained in the Combined Work and reverse engineering for
>>>>>>>> debugging such modifications ..."
>>>>>>>>
>>>>>>>> I am guessing that this applies to Eigen and it allows anyone the
>>>>>>>> right to reverse engineer a proprietary application for the purpose of
>>>>>>>> debugging Eigen. Am I right? If that is the case, this would be a
>>>>>>>> concern because this section does not impose a clear limitation on
>>>>>>>> what reverse engineering means. To track a particular bug in Eigen,
>>>>>>>> which is intertwined with the original code, you may need access to
>>>>>>>> some top-secret-data-structure that the developers do not intend to
>>>>>>>> release. I would expect that this would be unacceptable to some of the
>>>>>>>> users of VTK.
>>>>>>>>
>>>>>>>> Sorry for making this complicated but such is life when mixing
>>>>>>>> open-source with proprietary app development.
>>>>>>>>
>>>>>>>> -berk
>>>>>>>>
>>>>>>>> On Sun, Jan 31, 2010 at 12:36 AM, Benoit Jacob <jacob.benoit.1 at gmail.com> wrote:
>>>>>>>>> Hi,
>>>>>>>>>
>>>>>>>>> [Re-sending now that I am subscribed to the list which is subscribers-only]
>>>>>>>>>
>>>>>>>>> I'm one of the developers of Eigen. Reading your e-mails and your
>>>>>>>>> concerns, I updated a bit the FAQ, see especially:
>>>>>>>>> http://eigen.tuxfamily.org/index.php?title=Licensing_FAQ#How_about_static_linking.3F_2
>>>>>>>>>
>>>>>>>>> Let me summarize things a little (just elaborating on what Marcus said).
>>>>>>>>>
>>>>>>>>> Executive Summary:
>>>>>>>>>
>>>>>>>>> The LGPL version 3 is fully applicable to template libraries and there
>>>>>>>>> simply is no issue at all with static linking, not even if VTK uses
>>>>>>>>> Eigen and then some application links statically to VTK.
>>>>>>>>>
>>>>>>>>> Explanation:
>>>>>>>>>
>>>>>>>>> First of all, the old LGPL version 2.1 did indeed have lots of issues
>>>>>>>>> with template libraries. That's why we don't use it for Eigen.
>>>>>>>>>
>>>>>>>>> The LGPL version 3 provides 3 different ways in why LGPL-licensed
>>>>>>>>> libraries may be used: these are Sections 3, 4, and 5.
>>>>>>>>>
>>>>>>>>> In the case of Eigen, the only of these sections that you have to read
>>>>>>>>> is Section 3. It covers the case of template libraries. Eigen is to be
>>>>>>>>> used entirely under Section 3.
>>>>>>>>>
>>>>>>>>> Section 3 is very simple, it's essentially the same thing as a
>>>>>>>>> 2-clause BSD license. That doesn't mean that LGPL=BSD, because there
>>>>>>>>> still is the fact that the LGPL prevents proprietary forks of Eigen
>>>>>>>>> itself.
>>>>>>>>>
>>>>>>>>> I would now like to address this concern:
>>>>>>>>>
>>>>>>>>>>> I disagree with this not being an issue. Adopting something licensed
>>>>>>>>>>> under LGPL as a
>>>>>>>>>>> core library in VTK is a bad idea since it would preclude anyone
>>>>>>>>>>> building a statically
>>>>>>>>>>> linked application using VTK - unless they were distributing all of
>>>>>>>>>>> the components
>>>>>>>>>>> required to relink.
>>>>>>>>>
>>>>>>>>> The "issues with statically linking to LGPL libraries" refer to
>>>>>>>>> Section 4, specifically 4.d.1. As I said, Section 4 simply doesn't
>>>>>>>>> apply to Eigen. The confusion comes from the fact that most LGPL
>>>>>>>>> libraries are used under Section 4 (e.g. Qt is) but Eigen is just a
>>>>>>>>> special case as it is a pure headers-only library with nothing to link
>>>>>>>>> to. Thus Eigen is used entirely under Section 3, thus bypassing
>>>>>>>>> Section 4 entirely, thus bypassing the issues with static linking in
>>>>>>>>> particular. Subsequently, it just doesn't matter that VTK is a binary
>>>>>>>>> library and not a headers-only library, because Section 4 just never
>>>>>>>>> was used in the first place.
>>>>>>>>>
>>>>>>>>> More details and explanations in the FAQ that Marcus already linked to:
>>>>>>>>> http://eigen.tuxfamily.org/index.php?title=Licensing_FAQ
>>>>>>>>>
>>>>>>>>> I hope that this addresses your concerns and am available if you need
>>>>>>>>> more explanations, or disagree with mine!
>>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>> Benoit
>>>>>>>>> _______________________________________________
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>>>>>>>>>
>>>>>>>>
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>>>>>>
>>>>>
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>>>
>>>
>>>
>>> --
>>> ___________________________________________
>>> Andrew J. P. Maclean
>>> Centre for Autonomous Systems
>>> The Rose Street Building J04
>>> The University of Sydney  2006  NSW
>>> AUSTRALIA
>>> Ph: +61 2 9351 3283
>>> Fax: +61 2 9351 7474
>>> URL: http://www.acfr.usyd.edu.au/
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>>
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