[w3c sml] A question on "schema validity" (for MSM)

Michael,

 

I recently came across an article in which the author was being somewhat
critical of XML Schema.  One the arguments he adduced was the following.
Consider the following schema:

 

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"

       xmlns="http://www.example.com"
targetNamespace="http://www.example.com <http://www.example.com/> ">

 

    <xs:element name="foo">

       <xs:complexType/>

    </xs:element>

 

</xs:schema>

 

And the admittedly bogus document:

 

<bar />

 

According to this author, every XML Schema processor (he tried) reports
the document to be valid.  After your explanation of schema validity, I
doubt that this author placed a correct interpretation on the result of
his processors.  I suspect that validity="unknown" is actually reported
in the PSVI, and the processors didn't quite report that fact.  But I'm
not clear exactly what the reason for validity being unknown is.  (I can
imagine several reasons why this might be so, but I'm not sure which of
my imaginings is the correct one.)

 

The author concludes "If an application was relying on the W3C XML
Schema validation to screen out incorrect input, it would be in serious
trouble."  I believe your point was that that this conclusion is unfair.
The conclusion might better read, "If an application was relying on the
Schema validation to screen out "incorrect" [sic] input, the application
should have a more profound understanding of schema validity than this
author apparently has.  In particular, the application must have
specific knowledge of the results of the schema validation process."

 

Thank you.

 

 

Kirk Wilson, Ph.D.
CA Inc.
Research Staff Member, CA Labs
Intellectual Property and Standards
Council of Technical Excellence
W3C Advisory Committee Representative

Tele: + 1 603 823-7146
Fax:   + 1 603 823-7148
<mailto:kirk.wilson@ca.com>