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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Michael,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Thanks. I want to make sure I understand your first example
completely. Given the source XML:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><sample x=”banana cherry” /> and *<b><span
style='font-weight:bold'>no</span></b>* schema to validate against, the result
of the expression “if (@x = ('apple', 'pear', 'orange')) then <e/>
else <f/>” is atomized into an untyped atomic sequence that
consists of one value, “banana cherry”. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>If, however, there is a schema to validate against, and it defines
the type of “x” as NMTOKENS, then the result is a sequence of two
atomic NMTOKEN values, “banana” and “cherry”.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Do I understand this correctly?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>I do see from the example how nodes and (atomic) values interact, but
it seems to confirm my prior understanding of node trees since, in the example
given, the result of the @x expression is (first) a node whose value is (then)
atomized. So I’m still thinking initially of the node tree and then about
how a given node value is or is not atomized. What I’m not tracking with
is thinking of atomic values without, or apart from, nodes. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>In your second example, do you refer to this as a heterogeneous sequence
because in one case evaluating the expression results in an atomic value (perhaps
“final”), while in another it results in nothing (if there is no “status”
attribute)?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Thanks again,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Don<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<div>
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face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center tabindex=-1>
</span></font></div>
<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> Michael Kay
[mailto:mike@saxonica.com] <br>
<b><span style='font-weight:bold'>Sent:</span></b> Monday, May 07, 2007 4:11 PM<br>
<b><span style='font-weight:bold'>To:</span></b> Smith, Donald T.;
talk@x-query.com<br>
<b><span style='font-weight:bold'>Subject:</span></b> RE: [xquery-talk] items
as nodes or atomic values</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>When you write the expression</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>if (@x = ('apple', 'pear', 'orange')) then
<e/> else <f/></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>this is what happens.</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>1. The expression @x is evaluated. The
result of this expression is a sequence containing a single attribute node.</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>2. The result of (1) is atomized. If there
is no schema, the result is a sequence containing a single atomic value of type
xs:untypedAtomic. If there is a schema, however, that describes the type of @x
as xs:NMTOKENS and the actual value of @x is "banana cherry", then
the result of atomization is a sequence of two (atomic) xs:NMTOKEN values.</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>3. The result of (2) is compared with the
sequence-of-strings ('apple', 'pear', 'orange')</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>4. The result of the comparison in (3) is
a sequence containing a single xs:boolean value</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>I hope this shows how values consisting of
nodes and values consisting of atomic values interact, and how atomic values
can exist independently of nodes. In fact, XPath 1.0 allowed either sets of
nodes, or singleton atomic values. XPath 2.0 has generalized this to also allow
sets/sequences of atomic values, and singleton nodes.</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>In this example there are no heterogeneous
sequences, but they can arise and they can be very useful. Here's a handy
example:</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'><e status="{(@status,
'n/a')[1]}"/></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>which sets the value of the status
attribute on the new element to a copy of the status attribute of the context
node if it exists, or to the string 'n/a' otherwise. This involves a filter expression
in which the sequence being filtered contains an attribute node and a string.</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>Hope this helps!</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>Michael Kay</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'><a href="http://www.saxonica.com/">http://www.saxonica.com/</a></span></font><o:p></o:p></p>
<blockquote style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt;
margin-left:3.75pt;margin-top:5.0pt;margin-right:0in;margin-bottom:5.0pt'>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<div class=MsoNormal align=center style='text-align:center'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center tabIndex=-1>
</span></font></div>
<p class=MsoNormal style='margin-bottom:12.0pt'><b><font size=2 face=Tahoma><span
style='font-size:10.0pt;font-family:Tahoma;font-weight:bold'>From:</span></font></b><font
size=2 face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
talk-bounces@x-query.com [mailto:talk-bounces@x-query.com] <b><span
style='font-weight:bold'>On Behalf Of </span></b>Smith, Donald T.<br>
<b><span style='font-weight:bold'>Sent:</span></b> 07 May 2007 21:29<br>
<b><span style='font-weight:bold'>To:</span></b> talk@x-query.com<br>
<b><span style='font-weight:bold'>Subject:</span></b> [xquery-talk] items as
nodes or atomic values</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>This may be a well-worn question. If so, please point me to
the location of the discussion. Otherwise. . .<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I’m thinking through the XQuery/XPath data model. The
last paragraph in section 3.0 has me puzzling: “</span></font><span
lang=EN>The data model also supports values that are not nodes. Examples of
these are sequences of <a
href="http://www.w3.org/TR/2007/REC-xpath-datamodel-20070123/#dt-atomic-value#dt-atomic-value"
title="atomic value">atomic values</a>, or sequences mixing nodes and atomic
values. These are necessary to be able to represent the results of intermediate
expressions in the data model during expression processing.</span><font size=2
face=Arial><span style='font-size:10.0pt;font-family:Arial'>”<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I’m accustomed, from XPath 1.0, to thinking of
trees of nodes, so I’m not quite getting what it means to have items in
sequences that are either nodes or atomic values. Since an atomic value is a
string that conforms to an atomic type, atomic types are schema-defined, and
nodes may or may not have schema-defined datatypes, I don’t understand
the case where an atomic type would not be associated with – and so
represented by -- a node. In other words, I can’t image a XQuery/XPath
sequence as anything other than a node tree, which clearly shows I’m
still in XPath 1.0 land.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>The last line I quoted above indicates that this whole issue
arises from something that goes on during expression processing, so perhaps
this is an issue that only matters to those who write XQuery/XPath engines. At
any rate, if anyone can clarify this issue for me, I’d appreciate it.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Don Smith</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Information Architect<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>American Airlines<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>817-967-0310</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
</blockquote>
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