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RE: meaning of (salary, bonus)

From: Mary Fernandez <mff@research.att.com>
Date: 07 Jan 2003 21:54:31 -0500
To: Howard Katz <howardk@fatdog.com>
Cc: Michael Kay <Michael.Kay@softwareag.com>, www-ql@w3.org
Message-Id: <1041994473.1704.48.camel@squeak>

In the *sequence* expression: 

  (salary, bonus)

all salary elements will precede all bonus elements.

In the *path* expression:

  (salary, bonus)[. > 0]

the resulting salary and bonus elements whose content is greater
than zero will be in document order.  This is because
path expressions always yield sequences of nodes in document order
whereas sequence expressions yield sequences of nodes in input order.

On Tue, 2003-01-07 at 13:59, Howard Katz wrote:
> 
> Thanks Michael and everyone, that's helpful.
> 
> One additional question. I'm unclear about the concept of "document order"
> and when that applies in a comma-constructed sequence. Are *all* nodes in
> the sequence below in document order, or is the final node-sequence (before
> applying the predicate) the result of concatenating all <salary/> nodes in
> document order, followed separately by all <bonus/> nodes in document order?
> 
> >   (salary, bonus)[. > 0]
> 
> Howard
> 
> > -----Original Message-----
> > From: www-ql-request@w3.org [mailto:www-ql-request@w3.org]On Behalf Of
> > Kay, Michael
> > Sent: Tuesday, January 07, 2003 7:00 AM
> > To: Howard Katz; www-ql@w3.org
> > Subject: RE: meaning of (salary, bonus)
> > >
> > >      (salary, bonus)
> > >
> > > with the following commentary: "This expression contains all
> > > salary children of the context node followed by all bonus children"
> > >
> > > Can this expression be used outside a location path? I can
> > > see returning this expression as a function result, but can
> > > someone provide other examples of valid use? And in such a
> > > case, what is the meaning of "context node"?
> > >
> >
> > Sure, the expression can be used anywhere, for example
> >
> >   fn:average((salary, bonus))
> >
> > returns the average of this sequence - in this case it's actually the same
> > as
> >
> >   fn:average(salary | bonus)
> >
> > Or you could write:
> >
> >   (salary, bonus)[. > 0]
> >
> > to exclude the values that are negative.
> >
> > In fact, writing the expression within a location path is one of the least
> > useful places to use it, since the results of a path expression are always
> > in document order. So person/(salary,bonus) actually returns the
> > same result
> > as person/(salary|bonus).
> >
> > The "context node" is exactly what it would be if you wrote the expression
> > "salary" instead of "(salary, bonus)".
> >
> > Another common use case is when building a sequence recursively:
> >
> > <xsl:function name="reverse">
> >   <xsl:param name="p"/>
> >   <xsl:result select="if ($p)
> >                       then (reverse($p[position()!=1]), $p[1])
> >                       else ()"/>
> > </xsl:function>
> >
> >
> > Michael Kay
> >
> 
-- 
Mary Fernandez, Principal Technical Staff Member  
AT&T Labs - Research, 180 Park Ave., Room E243, Florham Park, NJ
07932-0971 
phone: 973-360-8679,  fax: 973-360-8187
mff@research.att.com, http://www.research.att.com/~mff  
Received on Tuesday, 7 January 2003 21:54:50 GMT

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