[xquery-talk] returning elements without duplicates, based on an XML schema and using an attribute as context node

[Philip Cantin]

Michael and Ken,

Thanks a bunch for your responses and help!

 Michael, I'll try and illustrate a bit better what I was trying to do
earlier.

I want the XQuery to determine if the @maxOccurs attribute exists in an
<xs:element> tag somewhere in the schema, and its value isn't 1. If this is
true, then, for all elements that have a @ref attribute in the schema
(because we now know there's at least one), the XQuery should get the string
value of the element's @ref attribute (what I wanted $name to be), along
with the value of element's @maxOccurs attribute (what i wanted $max to be),
and lastly the string value of $max (what I wanted $index_max to be). Then
finally, I just wanted to use these three values within an <xf:bind> tag
that was to be returned.

Also, I wanted to respond to few of your comments:


## note the exists(@maxOccurs) is redundant here. @maxOccurs != 1 always
returns false if @maxOccurs does not exist.

## it might be worth using a variable here to save doing the search twice
(or writing it twice).

---Thanks for the advice; at the moment I was going for getting the query to
work first, and optimization second, but I'll definitely change these things
once everything works the way it should.


## if your query is schema-aware, then @ref is a QName. Otherwise, it is a
string in the lexical form of a QName. Theoretically, you should be looking
for unique QNames, not unique strings.

---When you say the "query is schema-aware," are you referring to the editor
I am using to process the query (I'm using Altova XMLSpy), or the actual
query itself?


## This is pretty strange. $ref is an atomic value, so you can't use it on
the lhs of "/" or "//". Perhaps you wanted the attribute node? But which
attribute node: you're dealing with a group of @ref attributes that have the
same value. If $ref were a ref attribute (which it isn't), then you could
get the
maxOccurs attribute as $ref/../@maxOccurs

---Yes, I knew that code was completely incorrect. I was attempting to show
you the direction I wanted to go with my XPath expression, which was to find
the 'maxOccurs' attribute in an element based on where the 'ref' attribute
within the same element was.


~PJC


On Thu, Mar 26, 2009 at 12:15 PM, Michael Kay <mike at saxonica.com> wrote:



______________________________
>
> __
>
>        From: talk-bounces at x-query.com [mailto:talk-bounces at x-query.com] On
> Behalf Of Philip Cantin
>        Sent: 26 March 2009 15:50
>        To: talk at x-query.com
>        Subject: [xquery-talk] returning elements without duplicates,based
> on an XML schema and using an attribute as context node
>
>
>        Hello All,
>
>        I am new to this mailing list, as well as fairly new to XQuery and
> XPath (having learned it for a month or two). For the most part, I haven't
> had too much trouble editing an old XQuery document, until now.
>
>        I am trying to access the 'maxOccurs' attribute within the for-loop,
> where $ref is the 'ref' attribute, and return distinct <xf:bind> elements
> with no duplicate elements. However, I can't seem to set the $max variable
> properly using XPath functions, without getting an error. I imagine it must
> have something to do with setting/finding/using the current context.
>
>
>        The XQuery code looks like this:
>
>
>        if (exists($schema//xs:element[exists(@maxOccurs) and @maxOccurs !=
> '1']))
>
> ## note the exists(@maxOccurs) is redundant here. @maxOccurs != 1 always
> returns false if @maxOccurs does not exist.
>
>        then (
>           for $ref in
> distinct-values($schema//xs:element[exists(@maxOccurs) and @maxOccurs !=
> '1'
> and @maxOccurs ne 'unbounded']/@ref)
>
> ## it might be worth using a variable here to save doing the search twice
> (or writing it twice).
>
> ## if your query is schema-aware, then @ref is a QName. Otherwise, it is a
> string in the lexical form of a QName. Theoretically, you should be looking
> for unique QNames, not unique strings.
>
>              let $name := string($ref)
>              let $max := string($ref//following-sibling::maxOccurs)
>
> ## This is pretty strange. $ref is an atomic value, so you can't use it on
> the lhs of "/" or "//". Perhaps you wanted the attribute node? But which
> attribute node: you're dealing with a group of @ref attributes that have
> the
> same value.
>
> At this point I'm afraid I'm stuck, because you haven't given any clues
> about what the query is supposed to do, and it's hard to reverse engineer
> the requirements from incorrect code.
>
> >       Can someone show me the proper way to access the maxOccurs
> attribute
> from the ref attribute, and/or provide me with a link that can help me
> understand this situation a little more?
>
>
> If $ref were a ref attribute (which it isn't), then you could get the
> maxOccurs attribute as $ref/../@maxOccurs
>
> Michael Kay
> http://www.saxonica.com/
>
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