Re: Content constructors and sequences

I want to say THANK YOU to Jeni(!), David, Mike et al who are contributing
to this and similar threads.  It is a real education!

best,
-Rob


----- Original Message -----
From: "Jeni Tennison" <jeni@xxxxxxxxxxxxxxxx>
To: <xsl-list@xxxxxxxxxxxxxxxxxxxxxx>
Sent: Wednesday, January 09, 2002 2:32 PM
Subject: Re:  Content constructors and sequences


> Mark Nahabedian wrote:
> > Quoting Jeni Tennison <jeni@xxxxxxxxxxxxxxxx>:
> >> Putting it another way, sequence constructors can either construct
> >> sequences holding a number of documentless nodes, or a sequence
> >> containing any kind of items. It's a dynamic error if the result
> >> sequence contains documentless nodes and either simple typed values
> >> or pre-existing nodes.
> >
> > Why is it that the sequence itself can't be considered to be a
> > document?
>
> There are several sorts of answers to that question. At a high level,
> it's because of the way the XML Infoset and XML Schema describe XML
> documents - documents contain element and attribute information items
> which have values which are of different types. Text nodes do not have
> types, and of course they get merged together. More practically, a
> sequence can't be considered a document because a document cannot
> contain nodes from other documents, so treating them like documents
> would mean that sequences could only contain nodes from that document,
> rather than nodes from other documents. And that would make certain
> operations hard to handle because you'd lose context information (all
> the nodes in the sequence would have this document as their parent,
> for example).
>
> >> First, you could just not worry about it. An attribute's name is a
> >> xs:QName, which incorporates the namespace URI so there's no
> >> problem getting that namespace URI. If an attribute's typed value
> >> is a xs:QName or a list of xs:QNames (which it should be if the
> >> values have are qualified names), then each of those xs:QName
> >> values must have its own namespace URI accessible as well. So an
> >> attribute doesn't need namespace nodes. (Possibly - can you think
> >> of some examples where you need to access a namespace node given
> >> you have access to a QName?)
> >
> > This is admittedly a stretch, but the value of the attribute could
> > be a string containing QNames, for example, an XPath expression.
> > Then again, one could probably construct such a degenerate case in
> > 1.0 as well.
>
> That's a good point - an attribute value that contains QNames in some
> nested way. On the other hand, the parentless attribute that you're
> trying to get namespace information from is a parentless attribute
> that you've created elsewhere in the same stylesheet. If you're having
> to re-parse and understand information through an attribute value,
> then you should probably be redesigning your stylesheet! :)
>
> Cheers,
>
> Jeni
>
> ---
> Jeni Tennison
> http://www.jenitennison.com/
>
>
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