Consider this simple xml
<books>
<book>
<price ht="100" ttc="120"/>
</book>
<book>
<price ht="150" ttc="180"/>
</book>
</books>
I want to list the substraction of ttc and ht for all book/price node (ttc - ht)
I know how to obtain the ttc: //book[price]/price/@ttc and the ht same way.
How to obtain the result of ttc - ht ?
To retrieve the difference per book element, you can use this XSL code in combination with the Identity template:
<xsl:template match="book">
<xsl:copy>
<xsl:value-of select="price/@ttc - price/@ht" />
</xsl:copy>
</xsl:template>
It emits the difference for each <book> element.
To get the total difference of all <book> element's attributes, you can use the following XPath-1.0 expression:
<xsl:template match="books">
<xsl:copy>
<xsl:value-of select="sum(.//book/price/@ttc) - sum(.//book/price/@ht)" />
</xsl:copy>
</xsl:template>
The core XPath-1.0 expression is, starting from the level of <books>, this one:
sum(.//book/price/@ttc) - sum(.//book/price/@ht)
This expression subtracts all @ht attributes from all @ttc attributes. The .// operator means, that all descendant elements starting from the current axis are selected. In the above XSLT code, the current axis is <books>.
So in the above example case, the result is 50.