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Open Source and Free Documentation Licenses, Part 1: The GNU FDL
Pages: 1, 2

Section 3 also requires that if the copies distributed in quantity are Opaque, as defined above, Transparent copies of the Document must accompany each Opaque copy or be readily available to the public over a computer network. Transparent copies serve the same purpose in the documentation context that open source code does in the software context; i.e., making the creation and distribution of modified versions of the Document as easy as possible. While it would not be impossible to create a Transparent version of an Opaque copy of a document (for example, by scanning printed pages), the FDL encourages modification by putting the relatively minimal burden of making Transparent copies on the distributors of the licensed Documents, not the recipients. Obviously, the author or copyright holder is almost always in a better position to create a Transparent copy of a Document than the recipient of such a Document, because the author almost certainly created the Document in an electronic format with a word processor or text editor.

Section 4 addresses modifications to the original Document and is by far the most complex section of the FDL. However, almost all of the requirements of this section are structured around the two principles: first, that the modified Document be clearly identified as being distinct from the original Document, and second, that the original Document be clearly identified as a predecessor to the modified Document.

In order to keep the original and modified Documents distinct, the distributor of the modified version must:

  1. give a distinct title to the modified Document
  2. identify the authors of the modified Document
  3. state the name of the publisher of the modified Document on the cover page
  4. add an appropriate copyright notice for the modifications
  5. include a copy of the FDL and indicate that it applies to the modified Document.

The modified Document can't carry any endorsements that may have applied to the original Document--which makes sense, because anyone who may have endorsed the original Document endorsed a work different, however much or however little, than the modified Document.

In order to reflect the fact that the modified Document is derived from the original Document, the "Modified Version" must:

  1. contain a section entitled History (or add to one if there is one already in the original Document) listing the title, authors, and
  2. publisher of the original Document (and any of its predecessor Documents), as well as those of the modified Document
  3. list at least five of the authors of the original Document on the title page
  4. preserve and reprint all of the copyright notices applicable to the original Document
  5. preserve the Cover Texts and Invariant Sections, if any, from the original Document
  6. preserve the reference to the publicly available network location of the Transparent version of the original Document, if there is such
  7. preserve any Acknowledgments or Dedications section from the original Document in the modified Document.

While this list of conditions may seem quite daunting, for many documents, the task should be relatively straightforward. If there aren't any Invariant Sections, Endorsements, Acknowledgements, Dedications, or Cover Texts, the creator of the modified Document needs only to change the title, include a history section, list the author(s) of the original Document along with his or her own name, and, of course, license the modified Document under the FDL.

Much of the complexity of the FDL is due to its treatment of these "additional" sections--the Invariant Sections, Endorsements, Acknowledgements, Dedications, or Cover Texts--many (or all) of which are probably unnecessary to the real purposes of the Document. Authors who are considering using the FDL may want to forego the inclusion of this section in order to simplify others' compliance with the terms of the FDL and to encourage the free modification of their Document.

Nonetheless, the FDL permits the author of the modified Document to add his or her own versions of these sections--meaning that a modified Document, after several generations, could have a number of Front Cover and Back Cover Texts, as well as an extensive list of Invariant Sections, Acknowledgements and Dedications, all of which must be included in distributions "in quantity," and all of which, excepting Front Cover and Back Cover Texts, must be included in any distribution of the Document. This may, at some point, lead to undesirable results--it certainly could be possible, although unlikely, that such "surplus" sections could grow to be longer than the text of the "useful" part of the Document.

Distribution of a modified Document, once the conditions of Section 4 are satisfied, is exactly the same as for an original Document under either Section 2 or 3, depending on the circumstances (i.e., whether or not the distributor is distributing more than one hundred printed copies). Finally, Section 4 prohibits the use of the name of the author or the publisher of original Document for use in publicity or as an implied endorsement of the modified Document.

For a variety of reasons, authors may not want to encourage free modification of their works. Such authors should not use the FDL, but should use either one of the Creative Commons licenses or a variant on the Open Publication License.

The remainder of the FDL mainly addresses housecleaning and situations in which space can be saved by reprinting only one version of a particular text.

Section 5 address "Combining Documents." When two (or more) documents are both released under the FDL, the resulting Documents need have only one copy of the FDL itself attached and need not reprint more than one copy of identical Invariant Sections, such as, for example, if the Documents being combined were written by the same author who included the same philosophical explanation for his choice of the FDL with both Documents. Every other aspect of the FDL must be complied with in connection with both of the Documents: all Acknowledgements, Dedications, Cover Texts (if applicable), and non-identical Invariant Sections must be reproduced. The history section and list of authors must reflect both source Documents. Nota bene: Documents may be combined in this way only if both Documents are licensed under the FDL.

Section 6 applies to collections of Documents that are all licensed under the FDL. In such circumstances, the distribution of all the Documents need only have one copy of the FDL license text, but otherwise must comply with all of the license requirements with regard to each individual Document, with regard to Acknowledgements, Dedications, Invariant Sections, and so forth.

If the distributor wishes to reprint an FDL-licensed Document along with texts under other licenses, he or she may do so. Section 7 explicitly permits such a distribution so long as all of the requirements of the FDL are complied with regarding the FDL-licensed Document. Obviously, such a distribution must also comply with whatever other requirements are imposed by the licenses applicable to the other texts. The FDL will not apply to those other texts. A similar provision of the GPL permits copies of GPL- licensed programs to be distributed on the same media as non-GPL licensed programs, without violating the GPL. The distribution of works on the same media, however, is completely distinct from the combination of FDL and non-FDL licensed works (and GPL and non-GPL licensed works) which is not permitted by the FDL (or the GPL).

Section 8 addresses translations of Documents. This section states that translations are Modified Versions of the Document that must comply with all the requirements of Section 4. While the licensee producing such a translation may wish to translate Invariant Sections of the Document or the FDL itself, among other such texts, he or she may do so, but need not. The original, untranslated form of these texts, however, must be reproduced.

Section 9 addresses termination; that is to say, the effect of ending the relationship created by the license. This provision parallels a nearly identical section in the GPL. Any use, modification, or distribution of the Document other than as permitted by the FDL results in a termination of the putative licensee's rights under the FDL. If, however, such a licensee had distributed copies of the FDL-licensed documents to others prior to violating the FDL, those persons' rights remain unaffected by the breach.

The Free Software Foundation, the author of both the GPL and FDL licenses, does provide a list of licenses that it considers to be compatible with the GPL. Works under such licenses can be combined with GPL-licensed works without violating the GPL, at least in the eyes of the Free Software Foundation.

Section 10 simply states that the Free Software Foundation may issue different versions of the FDL that will have distinct sequential numbers. In the event that a licensee receives a work that is identified as being licensed under the FDL but that does not provide a version number, the licensee can choose any version of the FDL to apply to his or her use of the work.

Overall, the FDL provides a functional and detailed framework for the application of the license principles articulated in the GPL to documentation. For the most part, licensees have a clear idea of their rights and corresponding obligations under the FDL. The FDL guarantees that works licensed under it will be readily available for modification and distribution.

Nonetheless, there are some problems with the FDL, some the result of its philosophy and some as a result of drafting choices. In terms of its philosophy, the FDL creates complications by permitting authors to include Invariant Sections whose sole purpose seems to be to describe the relationship between the work's authors and the work. While the goal is a laudable one, it makes the license substantially more complicated, and perhaps worse, may swell the size of Documents over time because Invariant Sections cannot be changed or omitted.

In addition, the FDL has some ambiguities that could have been cleared up by slightly better drafting. The FDL contains a number of terms that are poorly defined: it's not clear, for example, whether Acknowledgements or Endorsements (or the Title Page, for that matter) are Invariant Sections, part of the Document, or Secondary Sections that need not be included. It seems more likely than not that they are intended to be either Invariant Sections or part of the Document (as the FDL seems to make clear that all of these elements must be contained in any copy or modification of the Document), but it would certainly clarify matters if there was language in the FDL to that effect. This a relatively minor failing, however.

Overall, the FDL provides a durable, relatively comprehensible framework for the licensing of documents. While it has not experienced anything near the success of the GPL, this likely was not intended. The FDL is more a companion to the GPL than a freestanding license. While numerous manuals and other technical documents have been licensed under the FDL, it is an open question whether the FDL will succeed outside of this relatively narrowly confined niche of materials that supplement GPL or other open source-licensed works.

In part two in this three-part series, Andrew will cover the Open Publication License. Stay tuned.

Andrew M. St. Laurent is an experienced lawyer with a long-time interest in intellectual property, particularly software licensing.


In August 2004, O'Reilly Media, Inc., released Understanding Open Source and Free Software Licensing.


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