Re: [xsl] Search for efficiency...(building nodes dynamically)

["andrew welch" <andrew.j.welch@xxxxxxxxx>]

On 3/2/06, Ahsan Ali <doubleletter@xxxxxxxxx> wrote:
> Hi all,
>
> I have an XML file of 6588 Airport elements as follows:
>
> <apt code="AAF" city="Apalachicola" country="United States"
> state="FL">Municipal Apt.</apt>
> ....
>
> In an XSLT program, I am processing yet another XML document that has
> the following format:
>
> <availabilitytable>
>         <avail>
>                 <origin>XYZ</origin>
>                 <destination>XYZ</destination>
>         </avail>
>
>         <avail>
>                 <origin>XYZ</origin>
>                 <destination>XYZ</destination>
>         </avail>
> </availabilitytable>
>
> These are an approx of 15-20 'avail' elements.
>
> The problem: I have written the XSL sheet in such a way that for every
> 'origin' and 'destination' element, the
> <apt> nodeset is traversed to get the airport name of a given code.
>
> Therefore, if there are duplicate origins/destinations (which is very
> probable in my case) there will be unnecessary multiple traversals.
>
> So I thought of building a nodeset of all origins/destinations,
> removing duplicates, and then looking up the <apt> file.
>
> The Question(s): Since I will need the result node later on in the XSL
> file, where do I store it ? And how do I build a result node like this
> ? If this is not feasible, what is the best method to avoid multiple
> traversals of such a large tree ?

Use a key:

<xsl:key name="airports-by-code" match="apt" use="@code"/>

then in your <origin> and <destination> templates:

<xsl:template match="origin">
  <xsl:apply-templates select="key('airports-by-code', .)"/>

You may have to do a little extra work to change the context to the
correct document - this is done differently between XSLT 1.0 or 2.0
but it's pretty trivial either way:

For 1.0, you have to change the context node to the airport XML using
a for-each, keeping track of the value of the origin node:

<xsl:template match="origin">
  <xsl:variable name="origin" select="."/>
  <xsl:for-each select="$airportsDoc">
    <xsl:apply-templates select="key('airports-by-code', $origin)"/>

For 2.0, you can use the 3rd argument of key() to specify the XML that
should keyed into:

<xsl:template match="origin">
  <xsl:apply-templates select="key('airports-by-code', ., $airportsDoc)"/>

Another great feature of 2.0!

cheers
andrew