Schematron: Use Phase for Errors and Warnings

Schematron allows for grouping of rules not only by XPath, but also through association using the “Phase” element. While this has long been recommended as an approach for improving validation performance and unit testing, Phase also serves as an excellent way to group together and differentiate between critical errors and simple warnings.

For example, an agency might choose to have some minimum data restrictions surrounding Officers and Agencies on a electronic citation that can not be overlooked, and at the same time have warnings surrounding statue codes that do not match the known state code values. In Schematron the following would the the code matching this scenario:

<!-- Rules resulting in just warnings (should not prevent submission) -->
<phase id="Warnings">
  <active pattern="validStatute"/>
</phase>
<!-- Rules resulting in errors (must prevent submission) -->
<phase id="Errors">
  <active pattern="minOfficerData"/>
  <active pattern="minAgencyData"/>
</phase>

The pattern attribute is an IDREF to a related pattern ID somewhere in the document. A developer can then create code to prevent the submission of any validation errors resulting from only one of the above phases. Schematron validation engines typically have command line switches or parameters to specify which phase should be run. For example, in Xerces’ implementation of Saxon, the parameter “phase=x” is used where x is one of the phase id’s listed above or “#ALL” if all phases should be processed.