Saxon extensions to XSD uniqueness and referential constraints
This extension is only available if enabled by specifying the attribute
saxon:extensions="id-xpath-syntax" on the
of the containing schema document.
With this extension enabled, restrictions are removed on the syntax allowed in the
field/@xpath attributes of the
Instead of the very limited XPath subset defined in the XSD 1.0 and XSD 1.1
specifications, Saxon will allow the same syntax as is permitted for streamable XPath
expressions in XSLT. Specifically, the syntax for both attributes is the same as allowed
select attribute of a streaming xsl:apply-templates, which is an extended
form of the XSLT 3.0 syntax for patterns. It permits, for example, any sequence of
downwards axes, arbitrary predicates on any step provided they do no downwards
selection, and conditional expressions.
For example, the following is permitted, indicating that US-based employees must have a unique social security number, but not imposing any such constraint on other employees:<xs:element name="company"> <xs:unique> <xs:selector xpath="employee[@location='us']"/> <xs:field xpath="@ssid"/> </xs:unique> </xs:element>