Analyze XML doc using XSLT

shumba · March 23rd, 2006, 02:19 PM

Hi,

Using my computer example, I want to use XSLT to figure out when to take my computer for servicing. My example doc is show below

Code:

<computer name="DELL XPS" service-year="2005">
   <component number="1" name="chassis">
      <expected-life years="6"/>
      <description>some chasis description</description>
   </component>
   <component number="2" name="hard-disk">
      <expected-life years="4"/>
      <description>some hard-disk description</description>
   </component>
   <component number="5" name="screen">
      <expected-life years="3"/>
      <description>some screen description</description>
   </component>
   <component number="4" name="keyboard">
      <expected-life years="3"/>
      <description>some keyboard description</description>
   </component>
   <component number="5" name="usb">
      <expected-life years="5"/>
      <description>some usb description</description>
   </component>
   <component number="6" name="mic">
      <expected-life years="2"/>
      <description>some keyboard description</description>
   </component>
   <component number="5" name="mouse">
      <expected-life years="1"/>
      <description>some usb description</description>
   </component>
</computer>

With my XSLT stylesheet, I want to ensure that I take the computer for repair if two or more parts have surpassed their expected life span(given by expected-life attribute). My document node has a service-year attribute to indicate when the computer was last service.

Therefore, I want to somehow go through the whole XML document and retrieve all the @years attributes(from the expected-life element) into a node set.

Then I want to be able to say when to take the PC for servicing once I find the two components that will fail first.

To this effect I am trying to write the stylesheet below but I am stuck. I am wondering if I am on the correct path.

Code:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
   <xsl:output method="html"/>
   <xsl:variable name="maxFailed">2</xsl:variable>
   <xsl:template match="computer">
      <xsl:apply-templates/>
   </xsl:template>
   <xsl:template match="component">
      <xsl:apply-templates/>
   </xsl:template>
   <xsl:template match="expected-life">
      part will fail after: <xsl:value-of select="@years"/> years
      <br/>
   </xsl:template>

   <xsl:template match="@* | node()"/>
</xsl:stylesheet>

Evidently, my stylesheet is incomplete as I am still working on it. I was wondering if I am on the right path. I think if I can get all the @years into a node set and then sort it, I can then just get the third entry in the node set and that the number of years after the last service date when my computer will fail.

Kind Regards,
Shumba

mhkay · March 23rd, 2006, 02:54 PM

I want to ensure that I take the computer for repair if two or more parts have surpassed their expected life span

with <computer> as context node:

<xsl:if test="count(component[expected-life/@years + ../service-year > $this-year])">
take it for repair
</xsl:if>

You're trying to do it procedurally, whereas this is a clear case for a declarative approach.

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference

shumba · March 23rd, 2006, 03:06 PM

Thanks for the help. I will try to do that.

The other issue is I am using XSLT 1.0 and do not have the current year($this-year) to hand. I guess I can use global variable or pass to the Stylesheet. Is there a way to get the current date in XSLT 1.0? I am aware this can be done in XSLT 2.0

I have been programming in C/C++/Java/Perl for ages and I just picked up XML/XSL about a month ago so I guess I am still wired to procedural gremlins.

shumba · March 23rd, 2006, 03:54 PM

ok. I had to correct the predicate to use ../@service-year.

Above this, I need to be able to say when I need to take for repair.

mhkay · March 23rd, 2006, 06:52 PM

The simplest way to get current date/year in XSLT 1.0 is to pass it as a stylesheet parameter (except possibly in client-side environments where calling Javascript might be easier).

Check whether your processor supports the EXSLT date/time extensions (www.exslt.org).

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference

shumba · March 24th, 2006, 05:19 PM

Thanks Micheal for your input.

I will venture into EXSLT to find out about the date/time support. I am doing something general purpose and I am not confident the client will have a processor that supports EXSLT. I will however go ahead and find out if they will.

I realised that I do not need to know the current date - I just need to be able to tell when the computer will fail.

If I know the last service date, then I can know when to take my computer for service when the third component exceeds it's expected life. So I sorted the components based on their expected life and the third entry in the node set will be how long from the service date the computer will need before it fails.

Stylesheet below.

Code:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
   <xsl:output method="html"/>
   <xsl:variable name="fail-index">3</xsl:variable>
   <xsl:template match="computer">
      <xsl:apply-templates select="component">

         <xsl:sort data-type="number" select="expected-life/@years"/>
      </xsl:apply-templates>
   </xsl:template>

   <xsl:template match="component">
      <!-- The components are sorted so we the computer will fail if ($fail-index -1) have failed. 
            The $fail-index position therefore gives as the first component that will require the computer
            to be taken for service-->
      <xsl:if test="position() = $fail-index"> The <xsl:value-of select="../@name"/> computer will
         fail in <xsl:value-of select="expected-life/@years + ancestor::node()
            /@service-year"/>
      </xsl:if>
      <xsl:apply-templates select="expected-life"/>
   </xsl:template>
</xsl:stylesheet>

If there is a better way to do this please advise.