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Re: [xml-dev] Holographic XML


You always ask the most intriguing questions.

SGML had the notion of groves, which were essentially collections of documents, and I think that we're moving back to that concept with XML Database collections and XQuery. In that respect I'd say that a document sequence is effectively three dimensional - the information tree being reducible to two dimensions, the sequence being the third, as sequence processing would effectively be orthogonal to the acyclic graph of an XML tree. 

By that same light, though I see RDF as being fractal, since RDF permits the introduction of cyclical graphs (this would be true as well of XML, where you have id/idref pairs, unless you specifically posited that cyclic graphs were not allowed). Indeed I think its arguable that RDF is holographic - you can in fact represent the n-dimensional aspect of RDF with a two dimensional structure, but only at the cost of potentially losing information. 

Kurt Cagle
XML Architect
Lockheed / US National Archives ERA Project

On Tue, Sep 7, 2010 at 11:46 AM, Costello, Roger L. <costello@mitre.org> wrote:
Hi Folks,

Just brainstorming ...


1. Holography is where the information about the 3 dimensions is stored in 2 dimensional space.

2. I've been told by industry experts that if you're not in the 3-D memory business in four years, you're not going to be in the memory business.


Operating in 3 dimensions seems to be something that will be increasingly important.

XML is kind of a 2 dimensional representation of data. How can XML expand to 3 dimensions?


Here are two responses from colleagues:

3-D storage is really only about increasing the size of an array.  There's no additional complexity, only increased space organized differently.

byte [1024][1024] twoD;
byte [1024][1024][1024] threeD;

Notice that the addressing and storage method are basically the same, but "threeD" is undeniably way bigger.

This analogy doesn't really carry over to XML.  You can't "increase the space" or density of an XML document, because it's already arbitrary according to the user's whim.  The only way I can possibly think to carry over the analogy to XML is to increase the "degrees of freedom" in an XML document by abandoning the hierarchy/rooted-tree constraint, and making it possible to represent arbitrary graphs.  (After all, trees are only a special case of graphs)  We can already do this today with RDF and other XML-serialized graph representations.  Notice that unlike 3-D storage, this introduces different semantics, not just another array dimension.  Good for some things, not for others.


I agree with David.  Along the notion of additional "degrees of freedom," check out "Colorful XML: One Hierarchy Isn't Enough" by Jagadish et al.:







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