Articles / notes on history of XML schema languages?

I'm writing up a short piece on the history of XML schema languages, and 
am looking for some good source material.  Any thoughts/suggestions?

The W3C XML schema specs (early drafts) reference notes that served as 
early input, but the connections (e.g. what input led to what XML schema 
design characteristic)  are not obvious (except in the minds of the 
schema spec contributors). It's also not clear if/how other ideas 
infiltrated into XML schema (why do OO concepts seem so prominent, for 
example?)

I'm also trying to uncover the history of other approaches, like 
Relax-NG, schematron, examplotron, etc. I've found lots of notes in 
XML-dev (and elsewhere) on this, but few summaries that tell a complete 
story.

I did found one nice summary , by Eric Van der Vlist:

http://www.idealliance.org/papers/xml02/slides/vandervlist/slides-schemas/html/slide1.html

But I'm hoping there might be others out there, somewhere [ maybe a 
audio file of Eric talking through his slides, and filling in all the 
details ;-) ]?

Best --

Ian
--
Ian Graham     < i a n . g r a h a m (at) u t o r o n t o . c a >