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   Re: [xml-dev] frustration (was RE: [xml-dev] XPath 2.0 )

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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:


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 

>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.



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