xml - explanation on duplicate attribute -

i have code on sample xslt , not make part exactly. want understand portion seq_no[/*/*/seq_no[@num = following::seq_no/@num]]. idea?

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/xsl/transform">     <xsl:output omit-xml-declaration="yes" indent="yes"/>     <xsl:strip-space elements="*"/>      <xsl:template match="node()|@*">         <xsl:copy>             <xsl:apply-templates select="node()|@*"/>         </xsl:copy>     </xsl:template>      <xsl:template match="seq_no[/*/*/seq_no[@num = following::seq_no/@num]]">         <seq_no num="[{count(preceding::seq_no)+1}]{.}">             <xsl:apply-templates/>         </seq_no>     </xsl:template> </xsl:stylesheet> 

and input

<xml>     <staff>         <seq_no num="0">0</seq_no>         <name>xyz</name>     </staff>     <staff>         <seq_no num="1">1</seq_no>         <name>xyz</name>     </staff>     <staff>         <seq_no num="1">2</seq_no>         <name>abc</name>     </staff>     <staff>         <seq_no num="3">3</seq_no>         <name>abc</name>     </staff> </xml> 

and output

<xml>    <staff>       <seq_no num="[1]0">0</seq_no>       <name>xyz</name>    </staff>    <staff>       <seq_no num="[2]1">1</seq_no>       <name>xyz</name>    </staff>    <staff>       <seq_no num="[3]2">2</seq_no>       <name>abc</name>    </staff>    <staff>       <seq_no num="[4]3">3</seq_no>       <name>abc</name>    </staff> </xml> 

you trying understand expression seq_no[/*/*/seq_no[@num = following::seq_no/@num]]. helps break down separate parts. consider following:

/*/*/seq_no 

because expression starts /, absolute path, , match seq_no element in document grand-child of root element of xml. quantify following xpath expression:

[@num = following::seq_no/@num] 

so, looking seq_no element num attribute has same value seq_no element follows in document. i.e have duplicated attribute further on in xml.

but fact absolute path here means not relative seq_no matching. so, if there exist duplicate anywhere in document, expression [/*/*/seq_no[@num = following::seq_no/@num] returns true, , template match seq_no elements in document.

note, not efficient, because evaluating expression each seq_no element in document, though have same value elements. may better once evaluate once variable, , use xsl:choose in template match determines whether need update attribute value.

try xslt, example

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/xsl/transform">    <xsl:output omit-xml-declaration="yes" indent="yes"/>    <xsl:strip-space elements="*"/>     <xsl:variable name="duplicate" select="/*/*/seq_no[@num = following::seq_no/@num]"/>     <xsl:template match="node()|@*">       <xsl:copy>          <xsl:apply-templates select="node()|@*"/>       </xsl:copy>    </xsl:template>     <xsl:template match="seq_no/@num">       <xsl:choose>          <xsl:when test="$duplicate">             <xsl:attribute name="num">                <xsl:number count="seq_no" level="any"/>                <xsl:value-of select="concat('[', ., ']')"/>             </xsl:attribute>          </xsl:when>          <xsl:otherwise>             <xsl:copy/>          </xsl:otherwise>       </xsl:choose>    </xsl:template> </xsl:stylesheet> 

note have changed template match num attribute here because part of xml transforming. also, using xsl:number counting too.