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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: frustration (was RE: XPath 2.0 )
Simon St. Laurent wrote:
>Okay, here's a noun:
>
> PSVI
>
>Here's a request to trim a feature (note the use of verbs):
>
> Drop PSVI. A lot of people claim they need it, but it's poorly conceived.
Thanks, I understood that. I'm much better at nouns.
First question - are you aware that XQuery does not rely directly on the
PSVI, but on the much simpler XML Query 1.0 and XPath 2.0 data model?
Here's a pointer to that document:
http://www.w3.org/TR/query-datamodel/
Much of this document is about the mapping from an XML Schema into the
simpler data model. The mappings for DTDs and well-formed XML have not yet
been completed - this is marked as an open issue in the document. The
result of the mapping is, IMHO, a rather simple and useful model. (This
mapping would have been a lot easier if the PSVI were designed at a
different level of abstraction, but we didn't have a lot of control over that).
So your first wish is granted. We get rid of the PSVI by mapping it into a
simpler model at a more useful level of abstraction. This model does have
datatypes.
>Repeat, with "strong typing" as the noun.
I know what you mean by this, and I think I also know how XML is used in a
loosely typed scenario, since I have thrown around my fair share of XML 1.0
untyped data too.
We have already had significant discussion of the usefulness of strong
typing for optimization and for catching errors. I think strong typing is
important for meeting goals like these:
- Suitability for combining data
- Optimizability for both physical XML and XML views of non-XML data
- Type safety and type-based optimizability
So this is the crux of our disagreement. You feel that a typed data model
(not the PSVI, but something much simpler) is not appropriate for XML, and
that strong typing is a bad idea. I disagree. Also, I think that XQuery has
done quite a bit to simplify the way the user interacts with the typed data
model, and don't think that global statements about XML Schema really say
that much about XQuery.
I don't think either of us can simply demand that the other adopt our
position, since neither of us really has the right personality to be
bullied into submission. And I don't think these are axioms that must be
adopted by all specs that are based on XML. I think that both typed access
and untyped access are important for XMl.
So I really do think that we need to find some way to construct more
detailed scenarios or arguments that will shed light on the virtues of our
two positions. This is going to take some time.
Perhaps I can construct some use cases for typing - I probably will not get
around to it right away. Right now, I'm largely gone for the next five
weeks, but I may find time to start on some typing use cases.
Jonathan
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