[xsl] positional predicates in XPath vs XQL

Subject: [xsl] positional predicates in XPath vs XQL
From: "Howard Katz" <howardk@xxxxxxxxxx>
Date: Fri, 23 Nov 2001 15:35:59 -0800
I'm implementing an engine that evaluates XPath. I'm currently working on
the part of the engine that implements positional predicates. I've
previously worked this out for location paths in XQL, but I think the
semantics are different in the two languages and want to make sure I
understand the differences.

In XQL if you say (pretending for the moment that positions start from 1 as
they do in XPath, rather than 0):

     /section/para[ 1 ]

and you have a tree that looks like this:

1  section
2       para
3       para
4  section
5       para
6  section
7       para
8       para
9       para

you'll get back this nodeset:

<2>, <5>, <7>

You can paraphrase this XQL query as saying, "Give me back the 1st child
node of each <section> element." Similarly, "/section/para[ 2 ]" returns
<3>, <8>, and if you say "/section/para[ 3 ]", you get back the single node,

To my understanding, the same location path in XPath only returns a single
node, <2>. Is my understanding correct?


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