xml-dev - RE: No Standard way to reference XML Schema? Was Re: (Many) XML Schema

[Michael Rossi <mrossi@crusher.jcals.csc.com>]

Andrew Layman wrote:
> 
<snip/>
> 
> Consider the case in which I have an e-commerce site that accepts purchase
> orders. The site advertises that it processes them according to a specific
> schema, one that supplies a default value of "US Dollar" for the currency
> units.  If I managed that site, I would not want to process purchase
orders
> that were similar, except that they specified a different schema in which
> the default currency units were "Greek Drachma".  My site would need to
> either (a) reject such purchase orders or (b) publish as part of the
site's
> description and/or legal conditions that it processes purchase orders
> according to the specific schema, regardless of any schemaLocation
> attributes in the document. Note that the second policy is actually more
> friendly towards the use of schemaLocation.
> 
> The bottom line is that, in processing a document, either the writer or
the
> reader makes the final determination of what processing happens.
Actually,
> only the reader does.
> 
> I hope this is helpful,
> Andrew Layman

   It certainly is helpful, thanks. But I'd still contend that we haven't
gained anything here. In this particular situation, the writer decided that
their purchase order was going to be written against a schema that specified
Greek Drachma as the unit of currency. If our e-commerce site chooses
(whether stated or not) to process this PO against it's own schema that uses
US Dollars, the consumer is going to end up paying the wrong amount for
their order. So our only choice is (a) above unless we either retrieve the
instance-specified schema or provide for some form of translation or
coercion. Maybe a stylesheet that would exchange the Drachma for Dollars and
vice-versa would be appropriate.

   Now it's still possible that there may be situations where applying some
non-instance-specified schema would be useful, although I can't think of one
at the moment. But in most, if not all, cases I think it's safe to assume
that if an instance has been written to conform to a particular schema,
there's likely a good reason why.

Michael A. Rossi
mailto:mrossi@jcals.csc.com
856-983-4400 x4911

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