Permissive and copyleft licences
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Styles of licensing free software and free content are often categorised into two approaches. One is "permissive", allowing the recipient to do what they like with what they make from the work, and the other is "copyleft", requiring the recipient to also make modified and derived works available as free software / free content.
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[edit] Software and technical works
In the free software community, some users and developers prefer permissive free software licences, while others prefer copyleft free software licences. Examples of the former include those of the BSD, Apache, and X11 projects. Examples of the latter are those of the GNU project. Software released under either style of these licence is considered "free", but the licences differ in the way that the source code can be redistributed. The relative merits and shortcomings of either is a common cause of flame wars.
The main copyleft software licence, the GNU General Public License (GPL) requires that software licensed with it continue to maintain the availability of source code and the FSF's "four freedoms" in perpetuity, and this includes both derivative works and forks of GPL licensed software. The BSD license only requires acknowledging the original authors, and imposes few restrictions on how the source code may be used. As a result, BSD code can be more easily integrated into or released entirely as proprietary software. For instance, parts of Mac OS X (Darwin) and the IP stack in Microsoft Windows (Winsock) are derived from BSD-licensed software.
Code licensed under the BSD license can be relicensed under the GPL (is "GPL-compatible") without securing the consent of all original authors. Code under the GPL cannot be relicensed under the BSD license without securing the consent of all original authors, since the BSD license does not require the source code to be always freely available. The Free Software Foundation provides the GNU Lesser General Public License that differs by having a weaker copyleft clause concerning linking between [LGPL] libraries and non-copyleft (proprietary or permissive) licensed code.
Supporters of the BSD license argue against the copyleft nature of the GPL. They argue that the BSD license is more free than the GPL, because it grants the right to do nearly anything with the source code, second only to software in the public domain, and that the nature of the BSD license has encouraged the inclusion of well-developed standard code into proprietary software. BSD supporters feel that the GPL takes away fundamental rights from the users, forcing them to write their own software for tasks that are covered by GPL software if they wish to redistribute it with a non-GPL-compatible license.
Existing BSD-licensed software distributions tend to avoid including software licensed under the GPL in the core operating system, except as a last resort when alternatives are non-existent or vastly less capable, such as with GCC. The OpenBSD project, for example, has acted to remove GPL-licensed tools in favour of BSD-licensed alternatives, some newly written and some adapted from older code.
GPL supporters believe (and emphasize) that mandating that derivative works should remain GPL-licensed fosters the growth of free software, as developers who use GPL code have to share their improvements with the community [if they want to distribute the derived works]. GPL supporters see the derivative work license requirement as more a form of power than a freedom, [1] and the BSD license as allowing people to "hoard" the work of others selfishly without having to give anything back.
[edit] Artistic works
Among authors, publishers, and users of documentation, art, and music, the concept of copyleft is newer and the debate of its definition is ongoing.
Lawrence Lessig, initiator of Creative Commons, contends that the implementation of copyleft is different for software and non-software works. He argues that while the GNU GPL prevents "free riders" in the field of software, it would fail to prevent free riders in artistic fields. For example, a newspaper could include a copylefted photo without having to make the whole article or paper freely available - because this is mere aggregation. Instead, he suggests that it is commercial activity that should make copyleft requirements kick in, instead of modification or publication.
Conversely, Eben Moglen has suggested that the use of "no-commercial-use" licences is overly restrictive.
[edit] References
[edit] See also
[edit] External links
- Freedom or Power? (Free Software Foundation) — describing "freedom" as freedom for all instead of one
- Open-source licensing: BSD is a better model (Network World) — advocacy for the permissive BSD license
- Open-source licensing: GPL is a better model (Network World) — advocacy for the copyleft GPL license
