XQL Challenge (also, Design for Queryability)

[Roger Costello]

Hi Folks,

I have created an XML document that contains Cellphone data.  
I have organized the data in this XML document similar to how
it might be organized in a database:

      - one subtree contains Cellphone hardware data (weight,
        battery, etc).
      - one subtree contains Cellphone feature data (caller id, one
        touch dialing, etc).
      - one subtree maps Cellphone hardware data to Cellphone feature
        data (in databases this would be called an "association
        table").

Why am I organizing the data in this fashion?  My hope is that
this approach will facilitate queryability of the data. That 
remains to be seen ...

Here's a sample query that I would like to perform:

"What features does the NOKIA 252 Cellphone have?"

If the data were in a database, such a query would be simple:

    SELECT features.name 
    FROM features, cellphones, cellphone-features
    WHERE features.id = cellphone-features.feature-id AND
          cellphone-features.cellphone-id = cellphones.id AND
          cellphones.brand = "NOKIA" AND
          cellphone.model = "252"

I am thinking (hoping) that I can perform a similar type of 
query using XQL.  Here's what I tried (among many other attempts):

cellphone-catalog/features
 [cellphone-catalog/cellphone-features/cellphone-feature/@feature-idref
= @id 
  $and$ 
 
cellphone-catalog/cellphone-features/cellphone-feature/@cellphone-idref
= 'NOKIA-252']

This XQL query doesn't work (it returns the empty set).

Below is sample data from my Cellphone XML document.  Any thoughts
on how to structure the XQL query?  /Roger

<?xml version="1.0"?>
<cellphone-catalog>
    <cellphones>
        <model brand="NOKIA" name="252" technology="analog"
id="NOKIA-252">
            <dimension units="inches">
                <height>6 5/8</height>
                <width>1 7/8</width>
                <thickness>1</thickness>
            </dimension>
            <weight units="ounces">6</weight>
            <battery type="nickel-cadmium">1100 mAh</battery>
            <talk-time units="minutes">132</talk-time>
            <standby-time units="hours">32</standby-time>
            <price currency="$US" with-contract="false">400</price>
            <price currency="$US" with-contract="true">180</price>
        </model>
    </cellphones>
    <features>
        <Authentication id="Authentication"/>
        <RingerAndEarpieceVolumeControl
id="RingerAndEarpieceVolumeControl"/>
        <BatteryStrengthIndicator id="BatteryStrengthIndicator"/>
        <AudibleKeypadControls id="AudibleKeypadControls"/>
        <DTMF-KeytoneSignalling id="DTMF-KeytoneSignalling"/>
        <One-YearPartsAndLaborWarranty
id="One-YearPartsAndLaborWarranty"/>
        <StoresNamesAndNumbers id="StoresNamesAndNumbers"/>
        <OneTouchDialing id="OneTouchDialing"/>
        <CallerID id="CallerID"/>
    </features>
    <cellphone-features>
        <cellphone-feature cellphone-idref="NOKIA-252"
feature-idref="OneTouchDialing"/>
        <cellphone-feature cellphone-idref="NOKIA-252"
feature-idref="CallerID"/>
    </cellphone-features>
</cellphone-catalog>


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