RDF vs. just XML

Re one question we discussed today: why use RDF rather than XML for the 
Accessibility Description Language (ADL)

Tim Berners-Lee answer is at http://www.w3.org/DesignIssues/RDF-XML.html

(It's part of his notes on design issues at 
http://www.w3.org/DesignIssues/Overview.html )

One of his points is quote

·       "The expression you need for querying something in terms of the XML 
tree is necessarily more complicated than the expression you need for 
querying something in terms of the RDF tree.

"This last is a big one. If you try to write down the expression for the 
author of a document where the information is in some arbitrary XML schema, 
you can probably do it though it may or may not be very pretty. If you try 
to combine more than one property into a combined expression, (give me a 
list of books by the same author as this one), saying it in XML gets too 
clumsy to consider."

end of quote

Now, the devil's advocate position would be: "the expressions are hidden 
from the end user anyway and maybe ADL will be so utterly simple that this 
consideration is minor"

So one of the things we'll want to look for is potential real-life 
assertions and queries that will indeed be far simpler to implement in RDF 
than in XML.

Len







--
Leonard R. Kasday, Ph.D.
Institute on Disabilities/UAP and Dept. of Electrical Engineering at Temple 
University
(215) 204-2247 (voice)                 (800) 750-7428 (TTY)
http://astro.temple.edu/~kasday         mailto:kasday@acm.org

Chair, W3C Web Accessibility Initiative Evaluation and Repair Tools Group
http://www.w3.org/WAI/ER/IG/

The WAVE web page accessibility evaluation assistant: 
http://www.temple.edu/inst_disabilities/piat/wave/