By Rachel Chalmers
After thirty years of development in secret, hypertext pioneer and visionary Ted Nelson has released the source code to his legendary, half-abandoned Xanadu, an important precursor to the world wide web. Work on it began in the sixties, but hardly any advances have been made in the last ten years. Now Nelson hopes to take advantage of the groundswell of support for open source software projects and revive interest in his fabled brainchild. At a sparsely attended session at the Open Source Summit in Monterey, California, Nelson announced that his Project Xanadu and the newly created Udanax.com have agreed to publish their code under the X11 open source license and to place their proprietary technical information in the public domain.
The first iteration of the Xanadu server software, written in C and more or less completed by 1988, is now published as Udanax Green. A second, more sophisticated version is based on a data structure discovered by K. Eric Drexler and called by him the Ent. This version is now Udanax Gold. Gold is incomplete, and it is Green that Nelson is encouraging open source developers to take for a test-drive. There’s also a demo client, written in Python and called Pyxi (for Python Xanadu Interface).
Who needs another electronic publishing system? Maybe all web users do. Xanadu has at least four crucial features that distinguish it from the web. First, its hypertext links are bi- directional, meaning that when an author quotes another document, the quoted document includes a reciprocal link to the derivative work. Second and more subtly, Xanadu supports transclusion. That means that the quoted portion is not a copy of the original but the relevant passage of the original object itself. Any changes to the original will change the transclusion in the derivative document.
Third, though the addresses in Xanadu’s docuverse look just like IP numbers, they are in fact infinitely extensible. That means no clumsy upgrade from IPv4 to IPv6. Finally and most dramatically of all, the entire system is version-controlled. Users can roll it back and forward through every state in which it has ever existed, making it easy to establish the exact time and nature of any changes. That means no more unannounced corrections and no more air-brushing the historical record. Anyone who’s done any serious content editing on the web will know exactly how priceless these additional features could be.
Incomplete and unproven as it is, Xanadu offers a conceptually powerful solution to the thorny problems of collaborative editing. As Byte columnist Jon Udell, who attended the meeting, writes: Nothing short of a radically different storage model and editing model will suffice, and Xanadu is those things. We all need to move beyond version control technologies that depend on filenames, directory structures and text pattern matching. Xanadu knows about each element of a document, uniquely, down to the granularity of one byte, and tracks the operations on those elements forever.
The release of Xanadu/Udanax under the X11 license has already provoked discussion on various publishing-related mailing lists. XML developer Orel Ben-Kiki urged programmers to consider integrating the sophistication of Xanadu with the popularity of existing World Wide Web Consortium standards. XML got started with a focus on separating content from presentation, he wrote. It got into pretty deep water when it started to address issues of linking, embedding, versioning and so on. Xanadu on the other hand seemed to focus on these issues, disregarding the presentation issues. So it would seem like each complements the other.
