Should we include a license notice for all third-party libraries used by Qt?

Question

I use Qt as a dynamically linked library, and I plan to use it with the LGPL license in software. Qt toolkit uses other libraries such as OpenGL, ANGLE, Libjpeg, Webkit to name a few. Even the QDate :: weekNumber () function is licensed by the University of California, Berkeley (see here ). Many of the third-party libraries are part of the core Qt modules.

Usually we need to include a license notice for the third-party programs / libraries that we use in our software. However, I'm not sure that in my license notice, should I include a license notice only about using the Qt tool library, or should I include a separate notification for each third-party library or code snippet used by Qt?

Another confusion is that some Qt contributions like KDE are licensed only with the GPL (not LGPL). How do people use the LGt licensed Qt library in this context?

Thanks!

Answer 1

Usually we indicate licenses from third-party components. You can find the list here: http://qt-project.org/doc/qt-5.0/qtdoc/licenses.html

Therefore, we follow the recommendations of Digia:

"Digia gratefully acknowledges these and other contributions to Qt. Recommend that programs using Qt also confirm these contributions and cite these license statements in the appendix to the documentation."

All KDE contributions in the core Qt libraries fall under the LGPL, even if they may have a different license elsewhere. This applies only to the main contributions of Qt, and not to external libraries from the KDE project.

Answer 2

General rule: if you have a licensed fragment of the GPL code, you are forced to release all the software / code base in accordance with the GPL license, because the GPL is viral and not permissive.

This is a fairly common problem, for example, when you work with the linux kernel, GPU developers always try to find alternative ways to directly link their code to the kernel, because the Linux kernel is the GPL and they want their drivers to be closed, the source and save all rights and sources.

The BSD-style license is much more permissive than the LGPL, I don’t think that you may run into problems with the BSD / MIT license, but when using the note while working with other people, it is always nice.

The real problem is that some censored markets, such as Apple and Microsoft, usually do not accept LGPL licensed software, so your application is likely to be censored and not published in such markets.

Speaking of limitations with the QT version of LGPL, the main limitation is that you are not allowed to link statically, and you can only dynamically link the link, you need to buy QT to respect the license and set the QT link statically.