XML::Schematron::Sablotron - Perl extension for validating XML with XPath/XSLT expressions.


  use XML::Schematron::Sabotron;
  my $pseudotron = XML::Schematron::Sablotron->new(schema => 'my_schema.xml');
  my $messages = $pseudotron->verify('my_doc.xml');

  if ($messages) {
      # we got warnings or errors during validation...

  OR, in an array context:

  my $pseudotron = XML::Schematron::Sablotron->new(schema => 'my_schema.xml');
  my @messages = $pseudotron->verify('my_doc.xml');

  OR, just get the generated xsl:

  my $pseudotron = XML::Schematron::Sablotron->new(schema => 'my_schema.xml');
  my $xsl = $pseudotron->dump_xsl; # returns the internal XSLT stylesheet.


XML::Schematron::Sablotron serves as a simple validator for XML based on Rick JELLIFFE's Schematron XSLT script. A Schematron schema defines a set of rules in the XPath language that are used to examine the contents of an XML document tree.

A simplified example:

   <rule context="page">
    <assert test="count(*)=count(title|body)">The page element may only contain title or body elements.</assert> 
    <assert test="@name">A page element must contain a name attribute.</assert> 
    <report test="string-length(@name) &lt; 5">A page element name attribute must be at least 5 characters long.</report> 

Note that an 'assert' rule will return if the result of the test expression is not true, while a 'report' rule will return only if the test expression evalutes to true.



The 'new' constructor accepts the following "named" arguments:

  • schema

    The filename of the schema to use for generating tests.

  • tests

    The tests argument is an alternative to the use of a schema as a means for defining the test stack. It should be a reference to a list of lists where the format of the sub-lists must conform to the following order:

      [$xpath_exp, $context, $message, $test_type, $pattern]

When called with a single scalar as its argument, this method sets/updates the schema file to be used for generatng tests. Otherwise, it simply returns the name of the schema file (if any).


When called with a reference to a list of lists as its argument (see the format in the description of the 'tests' argument to the new() method for details), this method sets the current test stack. Otherwise, it returns an arrayref to the current test stack (if any).


The add_test() method allows you push additional tests on to the stack before validation using the typical "hash of named parameters" style.

Arguments for this method:

  • expr (required)

    The XPath expression to evaluate.

  • context (required)

    An element name or XPath location to use as the context of the test expression.

  • type (required)

    The type argument must be set to either 'assert' or 'report'. Assert tests will return the associated message only if the the corresponding test expression is not true, while 'report' tests will return only if their associated test expression are true.

  • message (required)

    The text message to display when the test condition is met.

  • pattern (optional)

    Optional descriptive text for the returned message that allows a logical grouping of tests.


      $obj->add_test(expr => 'count(@*) > 0',
                     context => '/pattern',
                     message => 'Pattern should have at least one attribute',
                     type => 'assert',
                     pattern => 'Basic tests');

    Note that add_test() pushes a new test on to the existing test list, while tests() redefines the entire list.

verify('my_xml_file.xml' or $some_xml_string)

The verify() method takes the path to the XML document that you wish to validate, or a scalar containing the entire document as a string, as its sole argument. It returns the messages that are returned during validation. When called in an array context, this method returns an array of the messages generated during validation. When called in a scalar context, this method returns a concatenated string of all output.


The dump_xsl method will return the internal XSLT script created from your schema.


Internally, XML::Schematron::Sablotron uses the Sablotron XSLT proccessor and, while this proccessor is not 100% compliant with the XSLT spec at the time of this writing, it is evolving quickly and is very near completion. It is therefore possible that you might use a completely valid XSLT expression within one of your schema's tests that will cause this module to die unexpectedly.

For those platforms on which Sablotron is not available, please see the documentation for XML::Schematron::XPath (also in this distribution) for an alternative.


Kip Hampton,


Copyright (c) 2000 Kip Hampton. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.


For information about Schematron, sample schemas, and tutorials to help you write your own schmemas, please visit the Schematron homepage at:

For information about how to install Sablotron and the necessary XML::Sablotron Perl module, please see the Ginger Alliance homepage at:

For detailed information about the XPath syntax, please see the W3C XPath Specification at: