Translating from One XML Schema to Another

 

An XSLT style sheet can be applied to translate data from one XML grammar to another. Suppose that you receive stock quotes marked up in the following format:

<?xml version="1.0"?>
<investments>
  <item type="stock" exch="nyse"   symbol="ZCXM" company="zacx corp"
        price="28.875"/>
  <item type="stock" exch="nasdaq" symbol="ZFFX" company="zaffymat inc"
        price="92.250"/>
  <item type="stock" exch="nasdaq" symbol="ZYSZ" company="zysmergy inc"
        price="20.313"/>
</investments>

You want to add this information to your portfolio of the following format.

<?xml version="1.0"?>
<portfolio>
  <stock exchange="nyse">
    <name>zacx corp</name>
    <symbol>ZCXM</symbol>
    <price>28.875</price>
  </stock>
  <stock exchange="nasdaq">
    <name>zaffymat inc</name>
    <symbol>ZFFX</symbol>
    <price>92.250</price>
  </stock>
  <stock exchange="nasdaq">
    <name>zysmergy inc</name>
    <symbol>ZYSZ</symbol>
    <price>20.313</price>
  </stock>
</portfolio>

This amounts to translating from one XML schema to another. You can use XSLT to transform the <investments> data into the <portfolio> grammar. When you do this, your templates will contain output elements such as <stock>, instead of HTML elements. The following XSLT style sheet is an example.

<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
<xsl:output method="xml" indent="yes"/>
<xsl:template match="/">
  <portfolio>
    <xsl:for-each select="investments/item[@type='stock']">
      <stock>
        <xsl:attribute name="exchange">
            <xsl:value-of select="@exch"/>
        </xsl:attribute>
        <name><xsl:value-of select="@company"/></name>
        <symbol><xsl:value-of select="@symbol"/></symbol>
        <price><xsl:value-of select="@price"/></price>
      </stock>
    </xsl:for-each>
  </portfolio>
</xsl:template>

</xsl:stylesheet>

The translation can be performed in reverse with a similar style sheet, converting <portfolio> data to the <investments> grammar.

<?xml version="1.0"?>
<xsl:stylesheet version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" indent="yes"/>
<xsl:template match="/">
  <investments>
    <xsl:for-each select="portfolio/stock">
      <item type="stock">
        <xsl:attribute name="exch"><xsl:value-of select="@exchange"/></xsl:attribute>
        <xsl:attribute name="symbol"><xsl:value-of select="symbol"/></xsl:attribute>
        <xsl:attribute name="company"><xsl:value-of select="name"/></xsl:attribute>
        <xsl:attribute name="price"><xsl:value-of select="price"/></xsl:attribute>
      </item>
    </xsl:for-each>
  </investments>
</xsl:template>

</xsl:stylesheet>

Note that <xsl:attribute> is used not only to copy an attribute value to a new attribute, but also to convert element content to attribute values.