Schematron

Other Goodies

Namespaces

To be used in XPath expressions, namespaces must be declared using an ns element.

To validate an instance document such as the following:

<?xml version="1.0" encoding="UTF-8"?>
<library xmlns="http://ns.xmlschemata.org/examples/">
<book id="b0836217462" available="true">
<isbn>0836217462</isbn>
.../...
</book>
</library>

you would write a Schematron schema such as:

<schema xmlns="http://www.ascc.net/xml/schematron">
<ns uri="http://ns.xmlschemata.org/examples/" prefix="x"/>
<pattern name="main">
<rule context="x:book">
<assert test="@id">Missing "id" attribute.</assert>
<assert test="x:isbn">Missing "isbn" element.</assert>
<assert test="@id = concat('b', x:isbn)">The "id" attribute should be the ISBN number
with
a prefix "b" </assert>
</rule>
</pattern>
</schema>

Warning

When writing XPath expressions on documents with namespaces, you must remember that:

• XPath has no notion of a default namespace (elements from a namespace must always be prefixed in XPath expressions as done in the preceding example).

• The default namespace doesn't apply to attributes. (Attributes without prefixes in the instance document must not be prefixes in XPath expressions.)

Note

Languages such as XSLT and W3C XML Schema use XML namespace declarations (through xmlns attributes) to define the prefixes used in the content of their attributes.

This practice, known as "QNames" (for Qualified Names), is very controversial because it creates a dependency between the markup and the document content, ...