GNUFreeDocumentationLicense
The GNU Free Documentation License (GFDL) is a copyleft license for free content, designed by the Free Software Foundation (FSF) for the GNU project. The official text of version 1.2 of the license text can be found at http://www.gnu.org/copyleft/fdl.html.
The license is designed for software documentation and other reference and instructional materials. It stipulates that any copy of the material, even if modified, carry the same license. Those copies may be sold but, if produced in quantity, have to be made available in a format which facilitates further editing. Wikipedia is the largest documentation project to use this license.
When certain optional license features are invoked to label some sections of a document unmodifiable ("invariant"), some people, notably the Debian project, consider the resultant GFDL-licensed document to be "non-free", particularly under the Debian Free Software Guidelines [1] [2].
Secondary Sections
The license explicitly separates any kind of "Document" from "Secondary Sections", which may not be integrated with the Document, but exist as front-matter materials or appendices. Secondary sections can contain information regarding the author's or publisher's relationship to the subject matter, but not any subject matter itself. While the Document itself is wholly editable, and is essentially covered by a license equivalent to (but bothways incompatible with) the GNU General Public License, some of the secondary sections have various restrictions designed primarily to deal with proper attribution to previous authors.
Specifically, the authors of prior versions have to be acknowledged and certain "invariant sections" specified by the original author and dealing with his or her relationship to the subject matter may not be changed. If the material is modified, its title has to be changed (unless the prior authors give permission to retain the title). The license also has provisions for the handling of front-cover and back-cover texts of books, as well as for "History", "Acknowledgements", "Dedications" and "Endorsements" sections.
Using the GFDL
For a document to be covered by the GFDL, one must include a specific copyright and license notice.
Wikipedia and GFDL
All Wikipedia articles are licensed to the public under the GNU Free Documentation License. See for the details. The local copy of the license, as required by the terms of the GFDL, is at .
Materials for which commercial redistribution is prohibited
Materials for which commercial redistribution is prohibited can not be used in a GFDL-licensed document, e.g. a Wikipedia article, because the license does not exclude commercial re-use. However in some specific cases, commercial re-uses may be fair use and in that case such materials do not need to be licensed to fall within the GFDL if such fair use is covered by all potential subsequent uses. One good example of such liberal and commercial fair use is parody.
Related articles
External links
Here are resources discussing the appropriateness of the GFDL:
- http://people.debian.org/~srivasta/Position_Statement.xhtml - draft of Debian Position Statement about the GNU FDL
- http://home.twcny.rr.com/nerode/neroden/fdl.html - essay "Why You Shouldn't Use the GNU FDL"
- Why Wikitravel isn't GFDL: Problems with using the GFDL for short printed texts
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