W3C home > Mailing lists > Public > xsl-editors@w3.org > October to December 2001

An XPath function is needed for accessing the filter's parent context

From: Stanislav Vitebskiy <svitebskiy@pivotal.com>
Date: Wed, 19 Dec 2001 17:03:56 -0500 (EST)
To: <xsl-editors@w3.org>
Message-ID: <IIEGKHGKOIIIIGGCHNHAKEBFCCAA.svitebskiy@pivotal.com>
Here is a simple problem: select all the <customer> elements
that have <employee> sibling with the same 'name' attribute.
The solution is pretty obvious:
	customer[@name = ../employee/@name]

Lets now complicate the task a little. Let the name consist of
two parts, 'first-name' and 'last-name'.
Little complication - big problem: the technique shown above
will no longer work; there is no way to compare more than one
attribute of different elements, and there is no workaround in
the current version of XPath.

My suggestion (it could have been offered before, but I failed
to locate any mention of it) is to add a function that returns
the context against which the filter expression is being
evaluated. The example above can be rewritten like this:
	customer[../employee[@name = parent-context()/@name]]
In this case, parent-context() returns the <customer> element
against which <employee> siblings are being checked.

The advantage of this approach is that it can easily be extended
to comparing multiple attributes/elements/etc. The problem
described in the second paragraph (that XPath 1.0 cannot handle)
can now be solved by this expression:
	customer[../employee[
		@first-name = parent-context()/@first-name
		and
		@last-name = parent-context()/@last-name]]


PS., If you think that there is a better way to do it, or that
the current XPath can somehow tackle the problem described
here, please let us all know.
Received on Thursday, 20 December 2001 09:08:44 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 7 December 2009 10:59:52 GMT