[Bug 5476] xsi:schemaLocation should be a hint, should be MAY not SHOULD

http://www.w3.org/Bugs/Public/show_bug.cgi?id=5476





--- Comment #4 from Noah Mendelsohn <noah_mendelsohn@us.ibm.com>  2008-09-25 16:22:31 ---
> Some products indeed appear to have taken this to heart, and give
> users very little control over choice of a schema for validation,
> which makes a nonsense of the whole idea of validation - what use is
> validation if you can't control the choice of rules to be applied?

I think there are contexts in which that lack of control is exactly what I want
to implement.  Let's say I'm implementing, as I have done at least in prototype
form, a schema validator specifically optimized for and intended specifically
for use in a Web Services client.  In those scenarios, we very commonly want to
force the behavior that no network connections will be made by the validator,
and it's also typically the case that we would not trust a schema provided by
the document author if it were provided (if we trusted the document author,
than why validate in the first place.)  So, it's fine if I  by a processor that
implements both options, but that will implement a code path I never use.  I'll
always set it to not honor the "hint".  I think it's equally appropropriate for
me to use a processor that leaves out that unused code, and that just ignores
the hint.

As an aside, I've often thought that in such Web services scenarios what I'd
really want is to check that the URI provided for a schemaLocation, if any,
matches the one I as the receiver was expecting anyway.  For a purchase order,
for example, that would give one the comfort that:  you wrote the purchase
order with knowledge of the one fixed schema that I am going to use to validate
it.  This is particularly critical if we're going to depend on things like type
assignments, attribute value defaults etc.   I don't think we need modify our
recommendation to provide for this;  I think it's a service that particular
validation software can provide above and beyond the computation of the PSVI,
or as a precondition on whether to attempt validation at all, I.e. if I
discover that the author had in mind a different schema than the one I was
expecting, then punt, because the communication is known to be unreliable from
that one fact alone.


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Received on Thursday, 25 September 2008 16:23:10 UTC