Using XSLT 2.0 one possible solution is the following:

<xsl:stylesheet version="2.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 >
  <xsl:output omit-xml-declaration="yes" indent="yes"/>
 <xsl:template match="/">

   <xsl:for-each select="/*/*/order">
     <xsl:sort data-type="number" order="descending" select=
      "max(for $nItems in count(item),
               $i in 1 to $nItems,
               $j in  remove(1 to $nItems, $i)
                 return(item[$i]/@quantity
                       +
                        item[$j]/@quantity)
           )
      "
      />

      <xsl:if test="position() = 1">
        <xsl:for-each select="item">
          <xsl:sort order="descending" select="quantity"/>

          <xsl:if test="position() le 2">
            <xsl:sequence select="."/>
          </xsl:if>
        </xsl:for-each>
      </xsl:if>
   </xsl:for-each>

 </xsl:template>
</xsl:stylesheet>

When applied on the provided source xml document, the result is:

<item product-id="msft30" quantity="6"/>
<item product-id="sam2" quantity="2"/>


Cheers,
Dimitre Novatchev

"Bhavin" <v2desperado@g...> wrote in message 
news:1178076287.582665.124210@y......
>I need to write a complicated  X query. The Query is
> 1] which lists 2 most popular pairs of products bought together.
>
> and XML file is
>
> <e-store>
>   <product id="cre30" name="Creative ZEN VISION"
> price="255.99">Creative White 30GB USB 2.0 ZEN VISION Model
> 70PF115100011 - Retail</product>
>   <product id="ipod30" name="Apple iPod" price="236.99">Apple new
> iPod video Black 30GB Model MA446LL/A - Retail</product>
>   <product id="sam2" name="Samsung Black" price="154.99"> SAMSUNG
> Black 2GB USB 2.0 Audio Player with Built-in Speakers Model YP-K5JQB -
> Retail</product>
>   <product id="tosh60" name="Toshiba Piano Black" price="175.99">
> Recertified: TOSHIBA Piano Black 60GB USB 2.0 Portable Media Player
> Model MES60VK</product>
>   <product id="san4" name="SanDisk Sansa" price="135.99"> SanDisk
> Sansa e260 Black 4GB USB 2.0 MP3 Player Model SDMX44096A70 - Retail</
> product>
>   <product id="msft30" name="Microsoft Zune Black" price="223.99">
> Microsoft Zune Black 30GB Hi-Speed USB, Wi-Fi(802.11 b/g) Large color
> screen Digital media player Model JS8-00001 - Retail</product>
>   <product id="iaud2" name="iAUDIO Black" price="162.99">iAUDIO Black
> 2GB USB 2.0 Portable Video Player Model D2-2048BL - Retail</product>
>   <product id="arch30" name="ARCHOS Silver" price="255.99"> ARCHOS
> Silver 30GB USB 2.0 High-Speed Device (compatible USB 1.1): Mass
> Storage class (MSC) and Media Transport Protocol (MTP)</product>
>   <product id="ipod80" name="Apple iPod video" price="324.99"> Apple
> new iPod video Black 80GB Model MA450LL/A - Retail</product>
>   <product id="ipod2" name="Apple new iPod nano" price="142.99">Apple
> new iPod nano Silver 2GB Model MA477LL/A - Retail</product>
>
>   <warehouse address="NY">
>      <product-item product-id="cre30" quantity="5"/>
>      <product-item product-id="ipod30" quantity="3"/>
>      <product-item product-id="sam2" quantity="3"/>
>      <product-item product-id="tosh60" quantity="2"/>
>      <product-item product-id="san4" quantity="2"/>
>   </warehouse>
>
>   <warehouse address="TX">
>      <product-item product-id="cre30" quantity="5"/>
>      <product-item product-id="sam2" quantity="3"/>
>      <product-item product-id="san4" quantity="20"/>
>      <product-item product-id="msft30" quantity="1"/>
>      <product-item product-id="iaud2" quantity="2"/>
>      <product-item product-id="ipod2" quantity="4"/>
>   </warehouse>
>
>   <client name="John" address="Buffalo, NY">
>      <order order-date="2007-04-15" shipping-date="2007-04-18">
>         <item product-id="cre30" quantity="1"/>
> <item product-id="sam2" quantity="2"/>
> <item product-id="arch30" quantity="1"/>
> <item product-id="ipod80" quantity="4"/>
>      </order>
>      <order order-date="2007-04-15" shipping-date="2007-04-17">
>         <item product-id="cre30" quantity="1"/>
> <item product-id="ipod2" quantity="2"/>
> <item product-id="sam2" quantity="2"/>
>      </order>
>      <order order-date="2007-04-23">
>         <item product-id="msft30" quantity="6"/>
> <item product-id="sam2" quantity="2"/>
> <item product-id="ipod30" quantity="2"/>
>      </order>
>   </client>
>
>   <client name="Larry" address="Albany, NY">
>      <order order-date="2007-04-18" shipping-date="2007-04-20">
>         <item product-id="cre30" quantity="1"/>
> <item product-id="ipod2" quantity="1"/>
> <item product-id="sam2" quantity="1"/>
>      </order>
>      <order order-date="2007-04-18" shipping-date="2007-04-20">
>         <item product-id="sam2" quantity="1"/>
> <item product-id="ipod30" quantity="1"/>
> <item product-id="san4" quantity="1"/>
>      </order>
>      <order order-date="2007-04-22">
>         <item product-id="san4" quantity="1"/>
> <item product-id="sam2" quantity="2"/>
> <item product-id="iaud2" quantity="2"/>
>      </order>
>   </client>
>
>   <client name="Liz" address="Niagara Falls, NY">
>      <order order-date="2007-03-12" shipping-date="2007-03-14">
> <item product-id="san4" quantity="1"/>
> <item product-id="sam2" quantity="1"/>
> <item product-id="arch30" quantity="3"/>
>      </order>
>      <order order-date="2007-04-24">
> <item product-id="iaud2" quantity="1"/>
>      </order>
>   </client>
> </e-store>
>
>
> Actually I am new to X query and it is hard to implement using X Path.
> Any help will be really appreciated .
>
> Regards
>