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Mike,
> Now we are in the same position with XML Schema. This time it isn't
> short and it doesn't look simple, but again people are using schemas
> increasingly and we can't wish them away. I don't think it's
> acceptable, if people go to the trouble of defining the data types
> they are using in their documents, that XPath and XSLT should ignore
> this information and treat eveything as if it were text (or guess
> that it might be a number, as XPath 1.0 does). Anyway, we get
> messages every week on xsl-list from people asking how to manipulate
> dates. I would love to reduce the complexity of the solution, but I
> don't think we can deny that the requirement exists.
I completely agree that we need proper support for things like dates
and durations, and that supporting XML Schema built-in data types is
the best way to fulfil that requirement.
I'm guessing, but I think that when people express doubts and fears
about the impact of XML Schema on XPath they are more concerned over:
- the ability (or lack of it) to use XPath with documents that
haven't been validated against an XML Schema schema
- thinking that they'll have to understand XML Schema in order to
work with XPath 2.0
- the time that it's going to take for XPath 2.0 to be finalised
given the complexity of building in support for XML Schema
structures
- the possibility that unless time is taken over incorporating XML
Schema structures into XPath 2.0, it's not going to be done with
the elegance that characterises the namespace support in XPath 1.0
I don't think that there should be an issue with the first, because
what gets reported to the XPath processor is up to the XML parser
that's used with it. It's just that the data model WD doesn't yet
complete the sentences "Given information items that validate with
respect to a DTD, ..." and "Given information items from a document a
well-formed document, with no corresponding DTD or Schema...".
The second is a matter of reassurance. I don't think that there's
anything in XPath 2.0 that mandates that you use XML Schema types
explicitly. If you're not using XML Schema at all, I think that it all
works just the same way as XPath 1.0.
The latter two are more problematic. I can see why the WGs are
spending time on XML Schema structures, because it's much more
interesting than support for simple data types, which are far too...
well, simple... to challenge the intellects involved. And making up
new schema languages, as in the XQuery formal semantics, is always
fun. But if you want to talk requirements -- support for XML Schema
structures are pretty far from the requirements of current XSLT users,
especially compared to:
- dynamic evaluation of XPaths
- accessing enumerated values
- regular expressions
- date/time formatting
the first of which isn't ever going to be addressed, the second of
which doesn't look like it will be, and the latter two of which are
coming Real Soon Now.
I don't doubt that if complex types are eventually elegantly
incorporated into XPath then we'll use them with as few complaints as
we do qualified names (which isn't to say none!). But I think that
Simon's request for an XPath 1.5 is a request for an XPath that meets
*current* user requirements (by which I mean the requirements that
have been around for the last two years), within a reasonable
time-scale, and it seems clear that support for XML Schema structures
would be one of the first things to drop if that were the goal.
Cheers,
Jeni
---
Jeni Tennison
http://www.jenitennison.com/
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