Qt Licensing Explained

Qt Licensing Explained What are the Qt licensing options, and what should you consider when choosing the best Qt license for your project?

Copyright © 2009 Nokia Corporation and/or its subsidiary(-ies).

You have two licenses to choose from

• Licensing

Commercial LGPL

• Developed by Nokia • Keep all code

private • Keep your

distribution licensing options open

• Developed by Free Software Foundation

• Keep app code private, dynamically linked to Qt

• App licensing has some restrictions

More details on the next slides Copyright © 2009 Nokia Corporation and/or its subsidiary(-ies).

What is the Qt Commercial license?

• Proprietary license developed by Nokia • Allows you to keep all code private • Includes Qt standard support and updates • Allows you to choose license for distribution

… at time of distribution (more on the next slide)

Sorry, no mixing. A Qt user cannot combine commercial and LGPL in the same project. This is due to a restriction in the Qt Commercial License.


Choose your distribution licensing… at the time of distribution

• Not sure of which license you should choose? Postpone the selection of distribution licensing until the time of distribution.

• This is done by purchasing a commercial developer license and creating an application that dynamically links to the Qt libraries. In this case you can decide just prior to distribution whether to:

1.  Distribute your application with the commercially licensed Qt libraries, or 2.  Dynamically the application to the LGPL-licensed Qt libraries

• This also permits dual licensing of Qt-based applications

Not sure? Start commercial. Keep your distribution licensing options open.


What is the LGPL?

• LGPL stands for GNU Lesser General Public License • A license agreement written and copyrighted by the Free Software

Foundation • Nokia cannot modify the terms – it´s not our license. • The LGPL is a “copyleft” open source software license that is less

restrictive than the GPL (GNU General Public License)

What does this mean for you? You can freely use Qt under an LGPL license to create proprietary applications that dynamically link to the Qt libraries. (More later)


There are five factors to consider when selecting your license

1 2 4 5 3 We will cover each in more detail

in the coming slides.


1 Will you need to distribute your application externally?


• The requirements of the LGPL v. 2.1 only apply to externally distributed applications BUT note that you cannot change this after development has started due to a restriction in the Qt Commercial License Agreement.

• The LGPL only applies to externally distributed applications. If you are using Qt to create an internal application, take adequate precautions to make sure that the application is not distributed outside of the legal entity. Otherwise, you will need to comply with the LGPL v. 2.1 obligations.

1 Will you need to distribute your application externally?


2 Who is your target audience?


• You need to know if your target audience has restrictions against using open source licensed software.

• If they do, then don’t use Qt under the LGPL v. 2.1

• If your target audience will need to further modify Qt the LGPL may be a good choice unless these modifications to Qt represent a user’s commercial advantage and the user would not want to share them in source code format with downstream recipients.

2 Who is your target audience?


3 Will you need to modify Qt?


• You need to consider the implications regarding modification to Qt carefully

• If you modify Qt, you will need to distribute these modifications in source code format

3 Will you need to modify Qt?

Don´t want to share? Choose commerical. If you consider your modifications to represent a “competitive advantage” and you don’t want to distribute them in source code format, don’t choose the LGPL v. 2.1 license for Qt.


4 Will you need to statically link your application to the Qt libraries in order to optimize performance?


• There is debate within the legal and open source communities as to whether static linking is permitted under the LGPL v. 2.1 license

• This is due to an inconsistency in the LGPL v. 2.1 license itself regarding the definition of “works based on the Library” as the Library and derivative works of the library.

• Executables may be considered to be derivative works and this could result in the need to share the application source code

4 Will you need to statically link your application to the Qt libraries in order to optimize performance?

Tune out the static. Our recommendation is that you don´t statically link to the Qt libraries if you´re using the LGPL license.


5 Is the software architecture such that Qt will need to make calls to a proprietary component that is not “standard”?


• If Qt will make calls to a non-standard proprietary component you could have a license incompatibility if such proprietary component does not permit you to redistribute it.

• Section 6 states that “…the required form of the "work that uses the Library" must include any data and utility programs needed for reproducing the executable from it.”

• Materials “normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs” are exempted, unless the component itself accompanies the executable.

5 Is the software architecture such that Qt will need to make calls to a proprietary component that is not “standard”?


Summary/More info

• Nokia offers customers licensing options • Get your legal team involved early to make the right decision • Understand your obligations with LGPL • The Qt Commercial License give you options and full control

Licensing details at http://qt.nokia.com/licensing

Think commercial licensing is for you? Contact sales.


Qt Licensing Explained

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