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

[Benoit Jacob]

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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>