RE: [xsl] Testing 2 XML documents for equality - a solution

["Michael Kay" <mike@xxxxxxxxxxxx>]

First you need to specify what you mean by equality. This is a difficult
question. You could look to the spec of deep-equals() in XSLT 2.0 for
guidance, or to the Canonical XML definition. There's scope for endless
debate concerning issues such as comments, whitespace, namespace prefixes,
unused namespace declarations, and so on.

Your stylesheet will treat 

<a x="1" y="2"/>

and

<a y="2" x="1"/>

as being not equal, which is definitely wrong.

Algorithms based on concatenating the contents of both documents and then
comparing them as strings are likely to have the possibility of returning a
false equality.

An algorithm that uses recursive descent of both trees is likely to be much
faster in the case where the trees aren't equal. 

Michael Kay
http://www.saxonica.com/


> -----Original Message-----
> From: Mukul Gandhi [mailto:mukul_gandhi@xxxxxxxxx] 
> Sent: 30 March 2005 16:29
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: [xsl] Testing 2 XML documents for equality - a solution
> 
> Hello,
>   I was playing with XSLT. I thought could there be a
> nice way (with XSLT 1.0) to test 2 XML documents for
> equality. Two XML documents will be considered equal
> if all their nodes are identical(i.e. element, text,
> attribute, namespace etc).
> 
> I found few approaches for this in the FAQ (URL -
> http://www.dpawson.co.uk/xsl/sect2/N1777.html) .
> Indeed they are good work.. But I could come up with
> an elegant way. It uses no extension functions. Below
> is the XSLT .. 
> 
> <?xml version="1.0"?> 
> <xsl:stylesheet
> xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
> version="1.0">
>  
>  <xsl:output method="text" />  
>  
>  <!-- parameter for "ignoring white-space only text
> nodes" during comparison -->
>  <!-- if iws='y', "white-space only text nodes" will
> not be considered during comparison  -->
>  <xsl:param name="iws" />
>  
>  <xsl:variable name="doc1"
> select="document('file1.xml')" />
>  <xsl:variable name="doc2"
> select="document('file2.xml')" />
>  
>  <xsl:template match="/">
>  
>     <!-- store hash of 1st document into a variable;
>     it is concatination of name and values of all
> nodes -->
>     <xsl:variable name="one">
>       <xsl:for-each select="$doc1//@*">
>         <xsl:value-of select="name()" /><xsl:value-of
> select="." /> 
>       </xsl:for-each>
>       <xsl:choose>
>         <xsl:when test="$iws='y'">
>           <xsl:for-each
> select="$doc1//node()[not(normalize-space(self::text())
> = '')]">
>             <xsl:value-of select="name()"
> /><xsl:value-of select="." /> 
>           </xsl:for-each>
>         </xsl:when>
>         <xsl:otherwise>
>           <xsl:for-each select="$doc1//node()">
> 	    <xsl:value-of select="name()" /><xsl:value-of
> select="." /> 
>           </xsl:for-each>
>         </xsl:otherwise>
>       </xsl:choose>
>     </xsl:variable>  
>     
>     <!-- store hash of 2nd document into a variable;
>     it is concatination of name and values of all
> nodes -->
>     <xsl:variable name="two">
>       <xsl:for-each select="$doc2//@*">
>         <xsl:value-of select="name()" /><xsl:value-of
> select="." /> 
>       </xsl:for-each>
>       <xsl:choose>
>          <xsl:when test="$iws='y'">
>            <xsl:for-each
> select="$doc2//node()[not(normalize-space(self::text())
> = '')]">
>              <xsl:value-of select="name()"
> /><xsl:value-of select="." /> 
>            </xsl:for-each>
>          </xsl:when>
>          <xsl:otherwise>
>            <xsl:for-each select="$doc2//node()">
>       	     <xsl:value-of select="name()"
> /><xsl:value-of select="." /> 
>            </xsl:for-each>
>          </xsl:otherwise>
>       </xsl:choose>
>     </xsl:variable>  
>     <xsl:choose>
>       <xsl:when test="$one = $two">
>         Equal
>       </xsl:when>
>       <xsl:otherwise>
>         Not equal    
>       </xsl:otherwise>
>     </xsl:choose>
>  </xsl:template>
>  
> </xsl:stylesheet>
> 
> In this stylesheet, I am relying on 2 features -
> node() function and @* . node() function matches any
> node other than an attribute node and the root node.
> While @* matches any attribute. So I guess this XSLT
> can cater to all cases ;) . I have done limited
> testing with "element, text and attribute nodes only"
> and have got favourable results..
> 
> Another feature that I have incorporated in the
> stylesheet is, "controlling whether white space only
> text nodes should be considered during comparison".
> This is done with a stylesheet parameter iws. If it is
> "y", white space only text nodes will be ignored
> during comparison. If it is other than "y" or is not
> supplied, white space only text nodes will make a
> difference to the 2 documents.
> 
> If anybody cares to test this stylesheet and report
> any observations, I'll be happy!
> 
> Regards,
> Mukul
> 
> 
> 
> 		
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