No Standard way to reference XML Schema? Was Re: (Many) XML S chema Questions

[Andrew Layman]

You misread.  There _is_ a standard way for a document to indicate the
schema set (perhaps several schemas) its element information items conform
to.  That is the function of the schemaLocation attribute.  

What may be confusing you is that applications have the option to process a
document in ways not strictly mandated by those asserted schemas.  For
example, even today XML processors may elect to ignore an element's DOCTYPE
declaration. (See my other mails and also those of Henry Thompson for more
details.)

-----Original Message-----
From: Roger L. Costello [mailto:costello at mitre.org]
Sent: Thursday, December 30, 1999 4:04 AM
To: xml-dev at ic.ac.uk
Cc: www-xml-schema-comments at w3c.org; Schneider,John C.; Costello,Roger
L.; Cokus,Michael S.
Subject: No Standard way to reference XML Schema? Was Re: (Many) XML
Schema Questions


Hi Folks,

I gotta tell ya, this 'ol country boy is having a mighty difficult time
figuring out how an XML document is to indicate to that it conforms to
a  particular XML Schema.  It seems to me that this should be one area
that should be made crystal clear.  Instead, I am finding this to be one
of the murkiest parts of the XML Schema spec.

These statements really throw me through a loop:

"xsi:schemaLocation attribute serves as a hint, not a mandatory
directive. That is, the processor of an instance is welcome to look at
the URI referenced by the value of xsi:schemaLocation, but is not
required to."

"The means used to locate appropriate schema document(s) are processor
and application dependent"

I read these statements as saying that there is no standard way for
specifying in an XML document what XML Schema it conforms to - every XML
Parser will have its own way of doing things.  Really???   If this is
so, please, please tell me why this is a good thing.  I am struggling to
appreciate its beauty.    /Roger

Andrew Layman wrote:
> 
> What was said by Rick Jeliffe regarding the current schema draft is true
> (and anyone who is interested is recommended to red the actual XML Schema
WD
> at http://www.w3.org/TR/xmlschema-1/ and
http://www.w3.org/TR/xmlschema-2/.)
> 
> However, I would like to correct a possible misimpression that might arise
> from the turgid wording in the current public draft and also from Rick's
> statement "Then (s4.3.2) there is an attribute xsi:schemaLocation that can
> be put on any instance element. It allows the location of the schema to be
> declared. ..."
> 
> After extensive debate, the XML Schemas WG decided that the
> xsi:schemaLocation attribute serves as a hint, not a mandatory directive.
> That is, the processor of an instance is welcome to look at the URI
> referenced by the value of xsi:schemaLocation, but is not required to.  It
> may process an instance document using a different schema set (or no
schemas
> at all).  The relevant phrase is "unless directed otherwise" in the
> following passage from the 1999-12-17 structures draft:
> 
> "Again, unless directed otherwise general-purpose schema-aware processors
> must attempt to dereference each schema URI in the value of
"schemaLocation"
> to obtain a schema..."
> 
> This is in recognition of the fact that, ultimately, the processor of a
> document determines what processing is done.
> 
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