xsi:schemaLocation & Parser support?

[Prashanth Rao <prao@vitria.com>]

I'm a little baffled by what the XML Schema specification has to say about
xsi:schemaLocation and actual parser support for this feature.  Here's a
passage from the XML Schema Primer:

"1. In an instance document, the attribute xsi:schemaLocation provides hints
from the author to a processor regarding the location of schema
documents....The schemaLocation attribute contains pairs of values: The
first member of each pair is the namespace for which the second member is
the hint describing where to find to an appropriate schema document. The
presence of these hints does not require the processor to obtain or use the
cited schema documents, and the processor is free to use other schemas
obtained by any suitable means, or to use no schema at all."

The last sentence of the above paragraph indicates to me that
xsi:schemaLocation is an optional feature that parsers can choose to
implement or not.  This seems to go against the grain of the design
philosophy of XML:  "The number of optional features in XML is to be kept to
the absolute minimum, ideally zero."  I know that they are two separate
specifications, but by relegating xsi:schemaLocation to be an optional
feature, the specification breeds parser inconsistency, which surely can not
be a good thing.

Any thoughts on the matter?


Regards,
Prashanth Rao
Instructor
prao@vitria.com - 773-255-8743
Vitria - www.vitria.com - www.xmls.com