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

[Benoit Jacob]

2010/1/31 Bill Lorensen <bill.lorensen at gmail.com>:
> Benoit,
>
> So in the case of template libraries the license is sections
> 0,1,2,3,6.

Yes, exactly.

>
> And BSD is similar to an LGPL3 with sections
> 0,1,3

Yes, as far as I understand things, but IANAL. Section 0 is just
definitions, and section 6 by itself does not add any clause either.
So the real essential difference, for a pure template library, between
BSD and LGPL3, is Section 2, that controls modified versions (prevents
proprietary forks of Eigen itself).

> Section 2 still bothers me. We use and distribute several 3rd -party
> libraries with VTK. I think it is safe to say that we have modified
> everyone of them. These modifications are made not to add or modify
> functionality, but to bring the standards of the software in line with
> VTK's standards. In some cases, the 3rd parties agree to incorporate
> our changes in future releases. But this is not always the case.
>
> So if we modify and distribute the modifications, section 2a is
> confusing to me. If we don't satisfy the terms of 2a, then we fall
> into the GPL.

True, so it's indeed crucial that you satisfy the terms of 2a.
Fortunately, it's very easy. What it requires is just that:
i) You redistribute your modified Eigen under the LGPL3
ii) (unusual case, but handling it is what makes section 2a sound
clumsy) If your modified Eigen refers to an external function or data
that is not provided by your modified Eigen, then (the rest of) your
modified Eigen must still be usable without this external function or
data.

I don't see how you could end up even approaching the case handled by
ii) by just "bring[ing] the standards of the software in line with
VTK's standards". It seems to me that ii) is just trying to protect
from evil tricks to circumvent the LGPL's no-proprietary-fork
requirement.

> Also, the FAQ says the license is not complex, yet you need a
> multi-page FAQ to interpret it.

True, I'll edit the FAQ. What I meant is that it is not as complex as
the LGPL in the case of binary libraries, and is not as complex as its
reputation suggests. In our case the LGPL boils down to BSD +
interdiction of proprietary forks. Yet, it's true that it's still far
more complex than the BSD, but then again, most software licenses are.

> What concerns the Eigen developers about adopting a license like the
> one used by VTK?       VTK is not worried about proprietary forks. It
> is unlikely that a VTK fork could compete with the large VTK
> community's version of VTK.

It's a matter of personal opinions, and differences between different
open-source projects. I could give a few reasons why Eigen is not
going to adopt the BSD license, but that wouldn't advance the
discussion very far. Even if Eigen adopted the BSD license, there
would still remain all the LGPL libraries that you may want to use
(Qt...). In the end, the different major open source licenses are here
to stay, let's just all make sure that that doesn't prevent us
(various open source projects) from working with each other. Both LGPL
and BSD licenses are fine as they allow other projects to interact
with yours regardless of their own license!

Benoit


>
> Bill
>