THE XML REVOLUTION - TECHNOLOGIES FOR THE FUTURE WEB

Keys

- advanced node IDs for automatic construction of links

A key is a triple (node, name, value) associating a name-value pair to a tree node.

<xsl:key match="pattern" name="..." use="node set expression"/>: declares set of keys - one for each node matching the pattern and for each node in the node set

Extra XPath key function:

key(name expression, value expression): returns nodes with given key name and value

This is often used together with:

generate-id(singleton node-set expression): returns unique string identifying the given node

Example:

<xsl:key name="mykeys" match="section[@id]" use="@id"/> <xsl:template match="section"> <h1> <a name="{generate-id()}"> <xsl:number/> <xsl:apply-templates select="title"/> </a> </h1> <xsl:apply-templates select="body"/> </xsl:template> <xsl:template match="ref[@section]"> <a href="#{generate-id(key('mykeys',@section))}"> <xsl:for-each select="key('mykeys',@section)"> Section <xsl:number/> </xsl:for-each> </a> </xsl:template>

a key is declared for each section element with an id attribute
at each section title, a link anchor with a unique name is inserted
at each ref element with a section attribute, a link to the appropriate section is inserted using the key to locate the destination node
at the same time, both the section titles and the references are numbered

Comparison to DTD IDs:

keys are declared in the stylesheet (not in the DTD)
keys allow different "name spaces"
key values can be placed anywhere (not just as attributes)
one node may have several keys
keys need not be unique