A thread on Slashdot reopens the debate on copyrights for DTDs, asking how and why a DTD might be protected.

This question is probably as old as DTDs themselves, and has already been asked about SGML DTDs (see for instance this paper by Michael Erdle and Deeth Williams Wall).

The debate obviously has a legal facet. One of the issues being whether a DTD should be considered as a document, and protected by copyright, or if it should be considered as a computer program and protected by Intellectual Property Rights (IPR). A presentation by Cecilia Magnusson Sjöberg at XML Europe 2000 gives some interesting perspective on the subject, showing that while a DTD should probably be considered as a document, this might not be the case for a W3C XML Schema that gives more information about data processing.

The other facet of the debate discusses the reasons behind hiding or protecting a DTD whose goal is to define a standard:

No one ever made money on selling DTDs -- formats exist to be used, and keeping a "secret" DTD makes no sense as it can be easily reverse-engineered if someone really needed it. The only people who benefit from closed formats are ones that make their whole business model around selling software that implements them -- a model that is counterproductive for actual use of information.

The purpose of copyrighting a DTD appears then to be a protection against unwanted modifications rather than against its usage:

Since a DTD is a formal specification, you need to keep control over it. Ideally, once defined, it should never be allowed to change. If people can modify it as they like, then it becomes useless, since your XML documents may not conform to the modified versions.

And an artistic license might be a good fit:

A DTD is supposed to standardize data formatting, isn't it? Think less "copyleft" and more "standardized". This is one situation where the Artistic license makes sense, because it requires non-standard versions to be labeled as such.

The DocBook copyright notice came up several times as a reasonable protection for a DTD and something to borrow from.

Related story:

• XML-DEV as archive for prior art