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Open Source and Free Documentation Licenses, Part 1: The GNU FDL

by Andrew M. St. Laurent, author of Understanding Open Source and Free Software Licensing
09/16/2004

Open source and free software licensing is generally associated with software development, and for good reason. The ideas underlying open source licensing were all developed in the context of software creation. The very name "open source" refers to the opening of the source code in which software is written.

Open source principles make sense for software development. Because the source code is "open," users can make modifications to the underlying code, either in the form of incremental improvements or in the form of a total redevelopment that make the program into something entirely new. Code, at root, performs functions: the same code that allows searches in an airline database program may permit purchasers to select individual concert tickets in another program, with relatively little modification. It is the way that open source principles take advantage of the fluidity and power inherent in code that makes open source licensing so powerful.

To take advantage of these open source principles, open source licenses must at a minimum give users access to the source code, the legal ability to distribute the program both as source code and in executable form, and the ability to modify the source code to create new or derivative works which may themselves be freely distributed.

Related Reading

Understanding Open Source and Free Software Licensing
By Andrew M. St. Laurent

These same principles have also been applied to licenses for documentation and works other than software. Because documentation does not have the same fluidity and power that code does, it is an open question whether open source principles will prove to be as revolutionary in connection with such works as they have been with software. Nonetheless, at the very least, such licenses are useful, if for nothing else than the distribution of documentation and manuals related to open source programs.

The licenses discussed in this series of articles--the GNU Free Documentation License (FDL), the Open Publication License, and the Open Gaming License--are directed at documents in particular. They reflect a fundamental split in licensing philosophies associated with different groups of open source licenses. The GNU Free Documentation License, described in this article, applies to documents the same requirements of reciprocity applied by the GNU General Public License to software. That is to say, it requires that derivative works (modified versions of the original work, or works otherwise based on the original work) be licensed only under the GNU FDL. This is the so-called "viral" effect of the GNU system of licenses: works licensed under a GNU license, works derived from those works, works derived in turn from such derivative works, and on and on, can only be licensed under the GNU license under which the original work itself was licensed.

By contrast, the Open Publication License and the Open Gaming License, which will be discussed in the next two articles, follow the path of academic licenses such as the BSD and MIT licenses, at least in some variations, permit derivative works to be distributed under other licenses, including proprietary licenses, so long as certain conditions are complied with, mostly relating to providing notice of the name and publisher and the license applicable to the original work.

The Creative Commons project and the licenses associated with it represents a much more ambitious attempt to apply open source principles to a number of different media, including music, film, and performances, as well as written work. Those licenses are discussed in more detail in my book, Understanding Open Source and Free Software Licenses.

The GNU Free Documentation License

As can be deduced from its title, the GNU Free Documentation License applies the GNU licensing methodology embodied in the GNU General Public License (GPL) and the GNU Lesser General Public License (LGPL) to documentation that accompanies software, although it is applicable to other types of work. Its preamble states its purposes as, first, making "free" (in the sense of readily available for distribution) manuals, textbooks, and other useful written works and, second, assuring credit to the original author of the work. The license quite explicitly attaches the principle of copyleft to the licensed work, permitting the free distribution or modification of the work so long as the distributed or modified work is itself licensed under the GNU FDL.

The version of the license discussed in this article in v1.2, copyright 2002 by the Free Software Foundation. The complete text of the license is attached as Appendix A.

Any written work may fall within the scope of the GNU FDL so long as it has a notice that the license applies to it. The license only applies to copying, modifying, or distributing the work, all acts that would implicate rights created under copyright law. Like the GPL, the FDL does not apply to simple "use" of the work: anyone, for example, can read an GNU-FDL-licensed work without implicating the rights of the copyright holder or falling within the scope of the license. Finally, like the GPL, the FDL permits the distributors to charge money for physical copies--but they cannot limit the rights of those receiving copies to make copies or otherwise exercise their own rights under the FDL.

Although there are some ambiguities, the FDL at root requires that the substantive work itself (called the "Document" by the FDL) be open for modification and distribution. Certain texts, including those that relate only to licensing or to the original author's intended description of the work--either its title, or a brief paragraph intended for the back cover of the printed form of the Document--cannot be modified. These specific texts (which must be specifically identified by the author or copyright holder as texts that cannot be modified) must be distributed unmodified by licensees in connection with their distributions of the Document or modified versions of the Document.

The FDL permits essentially five different actions to be taken in connection with the Document:

  1. Verbatim copying.
  2. Verbatim copying in quantity.
  3. Modifying the document.
  4. Combining or collecting the work with other works issued under the FDL.
  5. Aggregating the work with other works under the FDL or other licenses.

Each of these five methods of distribution relies to varying extents on terms that are defined in Section 1, "Applicability and Definitions."

Section 1 definitions include the "Document," meaning the substantive work, for example a manual on Emacs called the Emacs Helper. A "Modified Version" is any version of the Document, whether translated, modified, or copied only in part. A "Secondary Section" is a piece of text, which is a part of the "Document," that does not address the subject matter of the document but instead deals with the relationship of the FDL to the intentions of the author or copyright holder. For example, the author of the Emacs Helper may want to include a short essay describing why he chose to use the FDL to license the Document. An "Invariant Section" is a Secondary Section that has been designated as "Invariant" and that must be included in redistributed versions. "Cover Texts" are short texts, five words for the Front-Cover Text and twenty five words for the Back-Cover Texts, designated by the original author. These Cover Texts are distinct from the title of the Document, which the FDL addresses separately. A Document need not have any Cover Texts, any Secondary Sections, or any Invariant Sections contained within it.

Section 1 also defines "Transparent" and "Opaque" versions of the Document. A "Transparent" version is the text equivalent of source code as that term is used in the GPL. A Transparent version of the Document is in a machine-readable format, in a file format that is readily modifiable using commonly available text editors; plain ASCII without markup is such a format. Note that a file in a proprietary format such as Microsoft Word is not Transparent under this definition. An "Opaque" version is any other version of the Document, including Documents printed on paper or in other formats not suitable for editing.

Finally, Section 1 permits but does not require warranty disclaimers to apply to the Document. Such disclaimers typically try to protect authors against liability for damages that might flow from the use of the work, or from infringement on the copyrights or other intellectual property rights of other authors.

Section 2 of the FDL is entitled "Verbatim Copying": it permits the most straightforward use of the Document licensed under the FDL. In order to do that, the person copying the Document, the licensee, need only copy the work exactly as it is, including the copyright notice and the license notice saying that the FDL applies to it. It also requires that a copy of the license accompany every such copy: if the author of the Work has not included such a copy, the licensee must attach a copy of the FDL text to the copy. Such copies must be distributed under the terms of the FDL with no additional terms attached. That means that any recipient of the Document has the exact same rights with respect to the Document that the licensee does, including the rights to modify or distribute the Document as provided by the FDL. The licensee can't use technical measures to restrict distribution, such as distributing the work in a way (like a locked PDF file) that would prevent copying or modifying the Work. The licensee need not copy or distribute the Front-Cover or Back-Cover Texts, if any. However, because the Secondary Sections are part of the Document, including any Invariant Sections, they must be included in distributions under Section 2. Similarly, if the Document has warranty disclaimers, the FDL considers those part of the license for distribution purposes. This means that any copy of the Document must have the warranty disclaimers, if any, that were attached to the Document in its original form.

Section 3 of the FDL addresses "Copying in Quantity." If the licensee distributes "printed copies" in quantities of more than a hundred copies, the licensee must abide by all of the requirements of Section 2 already described and must also abide by the provisions of Section 3. These provisions require the licensee to put the Front-Cover Texts on the front and the Back-Cover Texts on the back of copies. Section 3 also requires that the title of the Document be placed on the front cover of such printed copies. Such copies must also identify the licensee as the publisher of these copies on the front cover. Note that the licensor (usually the author of the Document) doesn't have to require that Cover Texts be distributed--in which case these additional requirements do not apply.

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