There may be little agreement on the question of what is the
license for free software, but there is, at least, a rough consensus on
what the options are. There are two basic varieties: GPL-like (which
require that derived products, if distributed, carry the same license) and
BSD-like (which only require retention of copyright notices and credit).
There are licenses which reserve special rights for the "primary
contributor," and other variations exist, but the basic choice is clear.
This is not the case for licenses covering documentation. There seems to
be little consensus on which rights authors need to retain, and which
should be relinquished. Indeed, there is little agreement on why
documentation should be free. Many of the reasons for keeping software
free (ability to look at the source to see how it works, ability to correct
misfeatures) do not apply to documentation. Obtaining a manual in
"original source" form may be helpful for cranking out more copies, but
that source will reveal little which is not already evident in the text.
Software, when distributed in binary form, is a black box which hides its
internal nature. Documentation, on the other hand, expresses its ideas on
its face; it is transparent.
Or, at least, it should be. Certainly your editor has produced writings
which fail on that front at times.
So why should documentation be free? Your editor has a renewed interest in
free documentation licenses for a couple of different contexts. One is a
longstanding item on LWN's "good intentions" list: putting our original
content under a free license. The other is the almost-imminent publication
of a book, which will certainly be released under free terms. In both
cases, the motivations are similar:
- Free software changes rapidly; its documentation has, in rare cases,
been known to lag a little behind. If the original author is unable
or unwilling to update a document to match current reality, somebody
else should be able to do so.
- Some readers never got the memo saying that English is The Language;
they can have funny ideas about having manuals in their own tongue.
It is rare that the original author can produce a translation in even
one alternative language, but there are often people with the interest
and skill who can do such translations. A free license should certainly
enable that work to happen.
- Collections of documents can be good things. Consider the massive "All
About Linux" books which were published in the mid-1990's, which were
generally made of the Linux Documentation Project's output, combined
with duct tape. Taking excerpts from free documentation can also be
useful; a book on Python database programming could benefit from, say,
Python and PostgreSQL introductions taken from other books.
- A printed book is unlikely to be available everywhere there might be
an interested reader, but a free, downloadable book is available
anywhere a net connection can be found.
For the purposes of updating and creating other sorts of derived works,
having the "original" source
of a free document is important - though not absolutely necessary. If
nothing else is available, a free license, a scanner, and some sort of
character recognition software can fill in. Translations and distribution
do not necessarily require source; PDF files may be all that is required.
Since not all free licenses are driven by the same goals, they do not all
require the distribution of a machine-editable version of the text.
Documentation licenses address one other area which is typically not an
issue with licenses applying to code: that of artistic integrity. Some
authors feel that their words should be distributed intact, or not at all;
others insist that certain types of material not be removed from their
works. A survey of documentation licenses will find a number of "thou
shalt not modify the text" terms. Such licenses will,
for the purposes of this article, be considered non-free. A document which
cannot be modified resembles a program which cannot be recompiled; it may
have its uses, but it is also a dead end.
The Creative Commons project is
trying to address the current impoverishment of the public domain by
encouraging the release of artistic works under any of a set of licenses.
Many of the creative commons licenses forbid the creation of derived works
or any sort of commercial use; they are thus, by this survey's standards,
non-free. There are two licenses which lack those terms, however, being
the Attribution 2.0
and Attribution-ShareAlike 2.0
The Creative Commons licenses are explicitly written as contracts; they
BY EXERCISING ANY RIGHTS TO THE WORK PROVIDED HERE, YOU ACCEPT AND
AGREE TO BE BOUND BY THE TERMS OF THIS LICENSE. THE LICENSOR GRANTS
YOU THE RIGHTS CONTAINED HERE IN CONSIDERATION OF YOUR ACCEPTANCE
OF SUCH TERMS AND CONDITIONS.
The Attribution license allows the creation and distribution of derived
works. Distributed copies must include a copy of the license - or at least
a URL pointing to it; additional restrictions may not be imposed on the
original work. Any distributed copy must include attribution giving credit
to the original author, along with the author's URL pointing to the
original version. The "ShareAlike" version of the license is GPL-like in
that it requires derived works to carry the same license.
Interestingly, the Creative Commons 2.0 licenses explicitly disclaim any
warranty or indemnification. Earlier versions of the license offered a
warranty by the author that he or she was entitled to offer the work under
The Creative Commons licenses say nothing about the format in which works
are distributed. By your editor's reading of the licenses, distribution of
a derived work in PDF format, with no availability of the work in its
original format, is allowed.
The GNU Free Documentation License
The GNU Project's recommended license for documentation is the Free Documentation License
it is complicated and, by some accounts, not truly free. In places, the
FDL has clearly been written with the idea of furthering the Free Software
Foundation's particular goals.
The FDL is GPL-like, in that it allows the creation and distribution of
modified versions, but any derived versions must carry the same license.
The FDL places limits on modifications, however. Any derived versions must
carry the original's "History," "Acknowledgments," and "Dedications"
sections, along with a full copy of the FDL. Beyond that, however, the FDL
creates the concepts of "invariant sections" and "cover texts"; these
features of the FDL are at the heart of the disagreement over its status as
a free license.
An invariant section is not allowed to address the primary topic of the
text. Instead, it deals with the "relationship" between the author(s) and
publisher and the subject:
The relationship could be a matter of historical connection with
the subject or with related matters, or of legal, commercial,
philosophical, ethical or political position regarding them.
The FDL requires that all invariant sections be included in any derived
work, and that, as indicated by their name, these sections not be
modified. The purpose of invariant sections is clear: it enables the GNU
project to include the GNU
Manifesto (and related texts) in manuals and to forbid its removal.
Thus, documents can be made to serve two roles: describing the subject
matter of interest, and promoting the agenda of the group which created the
"Cover texts" are short passages which must, in some conditions, appear on
the front and back cover of any distributed copy of the work. Use of cover
texts is only required when over 100 copies are being distributed.
Distributing large numbers of copies also obligates the distributor to make
a "transparent" version of the document - one which is machine editable -
available. The "transparent" copy need not be the original source; a plain
text file stripped of markup will do. People who distribute a small number
of copies can, if they wish, distribute them in an "opaque" format which
does not allow editing.
An FDL-licensed work with no invariant sections and no cover texts is, by
most peoples' reckoning, free. The inclusion of text which cannot be
modified or deleted obviously changes the picture, and many people consider
documents with those features to be non-free. Certainly the FDL makes
certain types of derived products, such as those using an excerpt from an
FDL-licensed work, difficult. An author wishing to take a few sections
GNU emacs manual must drag along the entire FDL, the entire GPL,
the GNU manifesto, the "Distribution" section, and the cover texts as
well. In practice, these requirements will make that sort of use almost
The FDL makes no statement with regard to warranties or indemnification,
other than to note that the document may carry warranty disclaimers outside
of the license. It is also careful to note that warranty disclaimers
cannot modify any other aspect of the license.
Open Publication License
The Open Publication License
(OPL) dates back to 1999. Among other things, it is used for the Perens Open Source
Series of books. The OPL is a relatively simple license; it allows
redistribution of works, with or without modifications, in any format. The
distributed copies must be licensed under the terms of the OPL, but nothing
in the license requires that an editable version be made available.
Modified versions must include a pointer back to the original, along with
the usual notifications that changes have been made. The OPL includes a
In its plain form, the OPL is a free license. It includes two "options,"
however, which can change the situation. "Option A" is a prohibition
on the distribution of "substantive" modifications - essentially anything
beyond reformatting or typo fixes. "Option B" is a restriction on
commercial redistribution. If either of these options is exercised, the
license becomes non-free. There does not appear to be anything prohibiting
a person who distributes a derived work from adding options to the license,
even if the original author chose not to use them.
The Creative Commons licenses and the FDL both include prohibitions on the
use of "technical measures" to deprive recipients of the works of their
rights under the license. The OPL, like many older licenses, has no such
requirement. An OPL-licensed document could, conceivably, be distributed
in some sort of DRM-infested electronic book format that, in practice,
deprived the reader of the right to copy or modify the document.
Common Documentation License
The Common Documentation
License was published by Apple Computer in 2001. It is a GPL-like
license, requiring that all derived works carry the same license. It makes
no requirement regarding credit to the original author beyond stating that
copyright notices must be preserved. Derived works need not carry a
pointer back to the original. Distribution in any format is allowed, with
no requirement to make an editable format available. There is no
restriction on the application of DRM schemes to CDL-licensed works. This
license does carry a strong warranty disclaimer.
Design Science License
The Design Science
License is, perhaps, the most direct attempt to translate the GPL into
the world of text. It allows the usual freedoms, but requires that all
derived works carry the same license.
The DSL takes a strong approach with regard to editable formats; it
requires that any person distributing the document make it available in
"the preferred form for editing." This requirement is rather firmer than
the FDL's terms; a plain text file will not suffice unless that is how the
work was created in the first place.
There is a warranty disclaimer in the DSL, though it does not explicitly
disclaim warranties of noninfringement.
A significant amount of documentation has been released under the BSD
license or the GPL. Putting a BSD-like license on a document makes some
sense; it allows any sort of use as long as the copyright notices are
preserved. Putting the GPL onto a document makes the author's intent clear
in an informal sort of way, but the GPL was not written for this sort of
application. The GPL refers explicitly to "programs" and acts like
compiling and running programs; how such language applies to documents is
unclear at best.
So which license would a grumpy editor use? Your editor co-authored a book which was
released under the FDL. But the next edition is unlikely to go out under
that license; the restrictions imposed by the FDL are simply too heavy.
Any of the remaining licenses described above would probably be usable,
though one of the licenses with a copyleft term looks preferable. No
decision has been made on that subject; stay tuned.
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