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Schematron

A short introduction to Schematron​

The purpose of Schematron files and their role in Semantic Treehouse.

Useful links:

Schematron structure​

See: http://www.datypic.com/sc/schematron/ss.html

Schema element <sch:schema>​

The top-level element of a Schematron schema.

A schema consists of <sch:phase>, <sch:pattern>, <sch:let> and other elements. The important elements are explained below.

Phase element <sch:phase>​

A grouping of patterns, to name and declare variations in schemas, for example, to support progressive validation.

Pattern element <sch:pattern>​

A set of rules giving constraints that are in some way related.

Let element <sch:let>​

A declaration of a named variable.

Common pitfalls and mistakes​

Rule context must be unique within a pattern​

See: http://schematron.com/2018/07/the-most-common-programming-error-with-schematron/

A node (xml elements) will only match one rule per pattern: the first one that matches.

So e.g. if you have the following rules:

<pattern>
    <rule id="r1" context="a"></rule>
    <rule id="r2" context="b"></rule>
    <rule id="r3" context="a | b"></rule>
    <rule id="r4" context="*"></rule>
</pattern>

When you validate a document with element <a>, it will only fire rule r1. Element <b> will only fire rule r2 and any other element will fire rule r4.

If you do want element <a> to fire rule r1, r3 and r4 you must place those rules in separate patterns, like so:

<pattern>
    <rule id="r1" context="a"></rule>
    <rule id="r2" context="b"></rule>
</pattern>
<pattern>
    <rule id="r3" context="a | b"></rule>
</pattern>
<pattern>
    <rule id="r4" context="*"></rule>
</pattern>

Choice the context right!​

Selecting attributes is not possible. The context must result in zero/one/more element nodes

E.g. this is NOT possible:

<rule context="//@currencyID" >
    <assert test=". = 'EUR'">The attribute currencyID must contain value 'EUR'.</assert>
</rule>

You should do this instead:

<rule context="//*[@currencyID]" >
    <assert test="@currencyID = 'EUR'">The attribute currencyID must contain value 'EUR'.</assert>
</rule>

Test schematron files​