Hi Folks,
A Schematron schema contains patterns. Each pattern contains rules. Each rule contains asserts.
I have large XML documents that I need to validate using Schematron. Each XML document is around 180 MB.
My Schematron schema has many rules. So, I figured that I would categorize
the set of rules and place each category of rules into a different pattern. That resulted in a Schematron schema with 30 patterns.
Validating an XML document against the Schematron schema was really slow.
“Why is validation so slow?” I wondered.
I did some digging and discovered the reason for the slowness. Recall that a Schematron schema is converted to an XSLT program. I looked at the XSLT program
that was generated for my Schematron schema. Here’s what I found:
<xsl:template
match="/">
<xsl:apply-templates
select="/"
mode="M0"/>
<xsl:apply-templates
select="/"
mode="M1"/>
<xsl:apply-templates
select="/"
mode="M2"/>
<xsl:apply-templates
select="/"
mode="M3"/>
…
<xsl:apply-templates
select="/"
mode="M29"/>
</xsl:template>
That says: Start at the top of the XML document and process the entire XML document, applying the template
rules with mode M0.
Then, start all over at the top of the XML document and process the entire XML document, applying the template rules with mode
M1.
And so forth.
So, the entire 180 MB XML file gets processed 30 times.
Eek!
It’s no wonder that validation was so slow.
My fix was to get rid of 29 patterns and put all the rules into one pattern. After doing that validation
ran much faster.
Lesson Learned:
If your Schematron schema must validate large XML documents, then use only one pattern in your Schematron schema.
/Roger
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