Dual-licensing is the practice of distributing software under two different sets of terms and conditions. This may mean two different licenses, or two different sets of licenses. Software is sometimes offered under more than two licenses, in which cases tri-licensing or multi-licensing may be a more accurate term.

When software is dual-licensed, recipients can choose which terms they want to use or distribute the software under. The distributor may or may not apply a fee to either option. The two usual motivations for dual-licensing are license compatibility and market segregation based business models.

Business models

This is commonly done to support free software business models. In this model, one option is a proprietary software license, which allows the possibility of creating proprietary applications derived from it, while the other license is a copyleft free software/open-source license, thus requiring any derived work to be released under the same license. The copyright holder of the software then typically gives away the free/open source version of the software at no cost, and profits by selling licenses to commercial operations looking to incorporate the software into their own business. This model can be compared to shareware.http://linuxinsider.com/story/38172.htmlhttp://linux.sys-con.com/read/49061.htm

One thing that is not clear yet is, what happens with derived work from third parties. The question here is, if the copyright holder of the original version is able to offer the derived work also within the commercial license. Usually a company hopes getting a lot of free work and help from open source coders. When using the GPL for example, there seems to be no possibility to use the free work of the community in the comercially licensed version as well. Some companies try to ship around this problem by writing their own licenses for the public version, wherein the coders of the open source community have to grant them an special right to publish their work under the commercial license as well.

Since in most cases only the copyright holder can change the licensing terms of a software, dual licensing is mostly used by companies that wholly own the software which they are licensing.

Dual licensing is used by the copyright holders of some free software packages advertising their willingness to distribute using both a copyleft free software license and a non-free software license. The latter license typically offers users the software as proprietary software or offers third parties the source code without copyleft provisions. Copyright holders are exercising the monopoly they're provided under copyright in this scenario, but also use dual licensing to discriminate the rights and freedoms different recipients receive.

Such licensing allows the holder to offer customisations, early releases, generate other derivative works or grant rights to third parties to redistribute proprietary versions all while offering everyone a free version of the software. Sharing the package as copyleft free software can benefit the copyright holder by receiving contributions from users and hackers of the free software community. These contributions can be the support of a dedicated user community, word of mouth marketing or modifications that are made available as stipulated by a copyleft license. However, a copyright holder's commitment to elude copyleft provisions and advertise proprietary redistributions risks losing confidence and support from free software users. http://www.gnu.org/philosophy/netscape-npl.html http://www.gnu.org/philosophy/apsl.html

Examples include MySQL AB's database, Mozilla Firefox, and Trolltech's Qt development toolkit.

As noted above, it is not clear if a copyright holder of an original version, that is dual licensed, is allowed to use the contributions of the open source community for the commercial licensed version. So the argument for dual licensing can't really be to make money on the one side, and get a lot of free work done by open source community members on the other side.

License compatibility

A second use of dual-licensing with free software is for license compatibility, allowing code from differently licensed free software projects to be combined, or to provide users the preference to pick a license.

Examples include the source code of Mozilla Application Suite, Mozilla Thunderbird and Mozilla Firefox, which is tri-licensed under the Mozilla Public License (MPL), GNU General Public License (GPL) and GNU Lesser General Public License (LGPL);^[1] and Perl, which is dual-licensed under the GPL and Artistic License.^[2]

Market segregation in proprietary software

Dual licensing is also used by some distributors of non-free software. Sometimes this is done to proprietary software to segregate a market. By splitting people into multiple categories such as home users, professional users, and academic users, copyright holders can set different prices for each group. However, among proprietary software, it is more common "home edition" and "professional edition" be also differentiated by the software included, not just the license.

References

External links

• Dual Licensing information from OSS Watch
• Article "Does dual licensing threaten free software?" by Glyn Moody
• Article "The Dual-Licensing Model" by Don Marti
• Article "Dual Licensing: Having Your Cake and Eating It Too" by Philip H. Albert
• Article "Dual-Licensing Open Source Business Models" by Heather Meeker
• Article "How to use open source as a power marketing tool" by John Koenig
• Paper "Dual Licensing in Open Source Software Industry" by Mikko Välimäki
• Dual Licensing Schemes
• "Should code be ?dual licensed? under the GPL and a permissive license?" by Software Freedom Law Center

de:Mehrfachlizenzierung es:Licencia dual fr:Licence double ja:????????? ru:??????? ?????????????? zh:???

---

Source: Wikipedia | The above article is available under the GNU FDL. | Edit this article