Terrific article Rick! Two excerpts that I especially like (highlight is my own): In order to get good quality-in-use out of a system, some way of providing process improvement and
continuous quality improvement can be implemented. In this case, when some problem in the system or markup is detected and addressed by developers and data entry staff, then a corresponding Schematron
rule is put into place. This allows the quality of the fix to be confirmed, and for information about the problem to be captured.
Diffing tools are more appropriate than Schematron for efficiency and detection; however,
they do not have any ability to explain the fault and they need customization to not report differences that may be irrelevant (order differences of semantically unordered elements, dropped obsolete
elements, etc.). From: Rick Jelliffe <rjelliffe@allette.com.au> For a Schematron introduction to this, including document invariants (fixed and co-occurrence) and input/output invariants, and
round-trip invariants, see Six Kinds of Validation using Schematron at
https://www.schematron.com/document/279.html For people interest in the practical theory of invariants, Bertam Meyers' work on Design by Contact still is a great place to start: he couches it in functional terms of pre-condition, invariant, post-condition, which I think is more systematic
than just "invariants". For the example, the Schematron IO validation (output to input) might be (roughly) <sch:pattern id="publicMilitaryIndicator-nullTransform" documents="'input.xml'">
<sch:let name="matching-output" value="myFunc:findMatchingRow(., 'output.xml')" /> <sch:assert test="TYPE = 'A' or TYPE = 'B' or TYPE = 'C'" role="pre-condition" >Every publicMilitaryIndicator input should have a TYPE with value A, b, or C (i.e., Civil, Joint, Military)</sch:assert> <sch:assert test="$matching-output/TYPE = 'A' or $matching-output/TYPE = 'B' or $matching-output/TYPE = 'C'" role="post-condition" >Every publicMilitaryIndicator output should have a TYPE with
value A, b, or C (i.e., Civil, Joint, Military)</sch:assert> <sch:assert test="$matching-output" role="invariant">Every input publicMilitaryIndicator should have a matching output</sch:assert> <sch:assert test="$matching-output/TYPE= ./TYPE" role="invariant" >Every input publicMilitaryIndicator TYPE value should be carried through to the output</sch:assert> </sch:rule></sch:pattern> Rick |