The Q Public License (QPL) is a non-copyleft free software license created by Trolltech for its free edition of the Qt toolkit. It captures the general meaning of the GNU General Public Licence (GPL), but is incompatible with it, meaning that you cannot legally distribute products derived from both GPL'ed and QPL'ed code. It was used until Qt 3.0, as Trolltech toolkit version 4.0 was released under GPL version 2.

Opposition to the license

The Free Software Foundation, authors of the GPL, sum up their objections to the QPL:

This is a non-copyleft free software license which is incompatible with the GNU GPL. It also causes major practical inconvenience, because modified sources can only be distributed as patches.

We recommend that you avoid using the QPL for anything that you write, and use QPL-covered software packages only when absolutely necessary. However, this avoidance no longer applies to Qt itself, since Qt is now also released under the GNU GPL.

Since the QPL is incompatible with the GNU GPL, you cannot take a GPL-covered program and QPL-covered program and link them together, no matter how.

However, if you have written a program that uses QPL-covered library (called FOO), and you want to release your program under the GNU GPL, you can easily do that. You can resolve the conflict for your program by adding a notice like this to it:

As a special exception, you have permission to link this program

with the FOO library and distribute executables, as long as you

follow the requirements of the GNU GPL in regard to all of the

software in the executable aside from FOO.

You can do this, legally, if you are the copyright holder for the program. Add it in the source files, after the notice that says the program is covered by the GNU GPL.

It also allowed Qt to change the license in later editions of its software, something often also provided in the GPL, and it was also frowned-upon that non-free use or development of derivatives was still not allowed. Only the personal edition of Qt was covered by the QPL; the commercial edition, which is functionally equal, is under a pay-per-use license and could not be freely distributed. As KDE, a desktop environment for Linux based on Qt, grew in popularity, the free software community urged Trolltech to put Qt under a license (the QPl) that would assure that it would remain free software forever and could be used and developed by commercial third-parties. Eventually, under pressure, Trolltech dual-licensed Qt for use under the terms of the GPL or the QPL.

All legal disputes about the license are settled in Oslo, Norway, but it has never been legally contested.

Adoption of the license

Other projects that have adopted the Q Public License, sometimes with a change in the choice of jurisdiction clause, include:

• The OCaml compiler and related tools from Projet Cristal at INRIA
• LibreSource is a versatile collaborative platform provided by artenum and dedicated to collaborative software development http://dev.libresource.org/
• Jpgraph is a graph generation tool written in PHP that dynamically produces charts and graphs as image files for presentation on websites.
• Hercules, a software implementation of the System/370, ESA/390, and z/Architecture mainframe computer architectures.

See also

• Open Source Licenses

External links

• The Q Public License, version 1.0

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