Schematron Overview

Roger Costello

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Validation

• A Schematron schema and an XML instance document are sent into a Schematron validator, which validates the instance document against the Schematron schema.

Schematron schema and an XML instance document are sent into a Schematron validator, which validates the instance document against the Schematron schema.

Validators

• GUI-based tools:
  • Oxygen XML: http://www.oxygenxml.com (Be sure to download version 8.2 or later; it has support for ISO Schematron)
  • Topologi (free!): http://www.topologi.com/products/validator/
• Dynamic validation:
  • There is an XSLT stylesheet which implements Schematron validation. So, an XML instance document can be dynamically validated against a Schematron schema by invoking any XSLT processor, such as SAXON or XALAN. For further details on dynamic validation, see the tutorial on dynamic Schematron validation.
• See Schematron Tools

Schematron Schema

• A Schematron schema is an XML document.
• The Schematron elements are in this namespace:
  • http://www.ascc.net/xml/schematron

1. <?xml version="1.0"?>
2. <sch:schema xmlns:sch="http://www.ascc.net/xml/schematron">
3. ...
4. </sch:schema>

• By convention, the filename of a Schematron schema has the suffix ".sch", for example: Check-Classifications.sch
• Also, by convention the namespace prefix used in Schematron schemas is "sch:", for example: sch:assert
  • (Note: I recommend that you always use the prefix "sch:" because some Schematron implementations expect it to be used)

Patterns

• A Schematron schema is comprised of one or more pattern elements:

1. <?xml version="1.0"?>
2. <sch:schema xmlns:sch="http://www.ascc.net/xml/schematron">
3. <sch:pattern name="..."> ... </sch:pattern>
4. <sch:pattern name="..."> ... </sch:pattern>
5. <sch:pattern name="..."> ... </sch:pattern>
6. </sch:schema>

• The purpose of each pattern is to specify a relationship that must exist among information in the XML instance document.

Rules

• A pattern element is comprised of one or more rule elements:

1. <sch:pattern name="...">
2. <sch:rule context="..."> ... </sch:rule>
3. <sch:rule context="..."> ... </sch:rule>
4. <sch:rule context="..."> ... </sch:rule>
5. </sch:pattern>

• The purpose of each rule is to specify a context node in the XML instance document, and assert a relationship relative to that context node.

Assertion

• A rule element is comprised of one or more assert elements:

1. <sch:rule context="...">
2. <sch:assert test="XPath">
3. ... text description ...
4. </sch:assert>
5. <sch:assert test="XPath">
6. ... text description ...
7. </sch:assert>
8. </sch:rule>

• The purpose of an assert element is to state a relationship that must exist in the XML instance document.

Assertion (cont.)

1. <sch:assert test="XPath">
2. ... text description ...
3. </sch:assert>

• The value of the test attribute is an XPath expression. A Schematron validator checks the XML instance document against the XPath expression. If the XPath evaluates to false then the XML instance document is not valid (and the validator generates an error message).
• The contents of <assert> is a human-readable version of the XPath expression.
• The validator evaluates every assertion within a rule and generates an error for every assertion that fails.

Validator Operation

• An instance document is validated as follows:
  • Visit each element in the XML instance document in document order,
  • For each element, examine the Schematron schema to see if there is a rule that specifies a context which matches the element; fire the first rule in each pattern that matches; process all assertions in the rule.