RE: [xml-dev] How to get XPath in a XSLT shylesheet

[noah_mendelsohn@us.ibm.com]

> > I've always thought augmenting XML through validation is a 
> > really bad idea
> 
> Hear hear. It was a particularly bad mistake to carry this forward from 
DTDs
> to schemas.

I mostly agree.  On the other hand, I note from the "Design Principles" 
section of the  XML Schema Requirements [1]:

"The XML schema language shall be [...] more expressive than XML DTDs; "

Questionnable as that goal may be, trying to meet it was a big deal for 
the workgroup.  I think part of the feeling was:  users out there have 
DTDs, they are going to expect to be able to rewrite their DTDs in XML 
Schema, and move away from using DTDs.   For better or worse, those users 
get to supply things like defaults, so schema better do the same thing. As 
far as I know, Schemas provides some means of doing pretty much everything 
a DTD can do, insofar as XML (the extensible markup language) allows for 
something other than DTDs.  In particular, we never found a way to provide 
entity definitions that XML 1.0 would believe were entity definitions, 
since XML 1.0 says those come only from DTDs.  (And, FWIW, those entity 
definitions also affect the content of the infoset resulting from a parsed 
document.)

I'm always intrigued at how many of the perceived shortcomings of a given 
project or language can be traced to setting the wrong requirements vs. 
doing the wrong implementation (though you can certainly make the case 
that XML Schema suffers from both in places.)  Then again, as with the 
adoption of SGML compatibility for XML, it's quite possible that if Schema 
had not advertised itself as a superset of DTDs, it would not in fact have 
gotten the widespread usage it has today. 

Noah


[1] http://www.w3.org/TR/NOTE-xml-schema-req#Principles

--------------------------------------
Noah Mendelsohn 
IBM Corporation
One Rogers Street
Cambridge, MA 02142
1-617-693-4036
--------------------------------------








"Michael Kay" <mike@saxonica.com>
01/10/2007 11:38 AM
 
        To:     "'Andrew Welch'" <andrew.j.welch@gmail.com>, "'David 
Carlisle'" <davidc@nag.co.uk>
        cc:     <xml-dev@lists.xml.org>, (bcc: Noah 
Mendelsohn/Cambridge/IBM)
        Subject:        RE: [xml-dev] How to get XPath in a XSLT 
shylesheet


> I've always thought augmenting XML through validation is a 
> really bad idea

Hear hear. It was a particularly bad mistake to carry this forward from 
DTDs
to schemas.

Michael Kay
http://www.saxonica.com/


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