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RE: XSLT and XQuery

• To: "'James Clark'" <jjc@j...>,<michael.h.kay@n...>,"'Jonathan Borden'" <jborden@m...>,"'David Carlisle'" <davidc@n...>,"'Jonathan Robie'" <jonathan.robie@s...>
• Subject: RE: XSLT and XQuery
• From: "Michael Kay" <michael.h.kay@n...>
• Date: Mon, 7 Jan 2002 10:08:16 -0000
• Cc: <www-xml-query-comments@w...>,<xml-dev@l...>
• Importance: Normal
• In-reply-to: <01d101c19730$83a30d50$0e00a8c0@b...>
• Reply-to: <michael.h.kay@n...>

> > Also, I've never understood why the descendant axis is
> supposedly easier to
> > statically type than the ancestor axis.
>
> Because the child axis is easier to statically type that the
> parent axis.
> The type of an element (in the XDuce/XQuery sense) tells you
> the possible
> attributes and children but doesn't tell you the possible
> parents.

Well, there are two possible scenarios. In a closed world, we know all the
types, in which case the type of the parent is the union of all types that
have "this" as a possible child or attribute. In an open world, we don't
know all the types, so the type of the parent is "any element or document
node". The only difficulty I can see is that of deciding whether the world
should be open or closed.

In any case, as a user, I'd much rather have a weakly-typed parent axis than
no parent axis at all.

I want to find all <section> elements whose depth in the tree is less than
4:
  //section[count(ancestor::* < 3)]

You're not going to let me write that because you don't know how to
type-check it? Gee thanks, I'll stick with XPath.

Mike Kay

• Follow-Ups:
  • Interesting XML-DIST-APP thread
    • From: Mike Champion <mc@x...>
  • Re: XSLT and XQuery
    • From: "James Clark" <jjc@j...>

• References:
  • Re: XSLT and XQuery
    • From: "James Clark" <jjc@j...>

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