Why dual licensing? Since we got a huge amount of requests for a proprietary license for RapidMiner (formerly YALE), we decided to develop RapidMiner according to a dual licensing model. In many cases users and developers embed RapidMiner as a core library into their application or improve RapidMiner for a customer by changing the graphical user interface, adding new operators, etc. Although it is possible to do this under the GPL under certain restrictions, some people demand for a proprietary license in order to fit their business model.

The dual license, by its name, has two licenses, one that we call the free license and the other one that we call the proprietary license. As free license, we use the GNU General Public License (GPL), which is the most commonly used free license. The GPL allows all users to use, copy, modify, and redistribute RapidMiner (formerly YALE) again under the GPL. If a licensee intends to distribute a modified version of RapidMiner (YALE) or a software using RapidMiner (YALE) or parts of RapidMiner (YALE) without releasing the source code of his software, he or she needs to obtain a proprietary license. But there are other reasons as well: customers get value added features like service plans, add-ons, and other bundled products as well as individual solutions and professional support.

As a developer using RapidMiner (YALE), you generally have two options:

• The first is to contribute to the Open Source community by placing your application under the GPL. This option secures all users the rights to obtain the application's full source code, modify it, and redistribute it again.
• The second option is to purchase a proprietary license from Rapid-I. This option secures you the right to distribute your application under the license terms of your choice and provide you additional services.

Please note that it is necessary to choose either the GPL or the proprietary license at the outset of development. Our license model does not allow you to start developing proprietary software using the GPL version.

Our long term goal is to ensure that the code bases of both versions are exactly the same and the only difference is the license under which they are used. This way everyone can use, modify, and enhance the GPL version as long as this is possible for him and can use the exact same version of RapidMiner (YALE) under a proprietary license if this is necessary. In order to achieve this goal, most RapidMiner development is done in-house.

Of course we highly appreciate contributions of the open-source community which help to further improve RapidMiner. Both, these contributions and the funding by proprietary licenses actually help to improve RapidMiner. We strongly believe that this leads to the best results for both the open-source version and the proprietary version users. This way, external development is possible, but we need to ensure that copyrights are assigned from contributors before their contribution is added in. However, we also want that the contributor can still keep the copyright for his or her work and therefore we use a Joint Copyright Assignment where both parties get the copyright for the contribution. This is a model similar to that of the content management system Mambo or that of the office software OpenOffice. Please use our Joint Copyright Assignment Form for this purpose (available on request).

There are several other tools available under a dual license including mySQL, Qt of Trolltech, and Asterisk.  Similar to these companies, we also believe that by a dual license we will achieve a maximum gain for all users of RapidMiner.