What Is an Assertion?

XSD Tutorials - Herong's Tutorial Examples - Version 5.11, by Dr. Herong Yang

XSD Tutorials - Herong's Tutorial Examples

∟What Is an Assertion?

This section describes assertion introduced in XSD 1.1. It you to specify any validation rules represented as XPath expressions on XML documents.

What Is an Assertion? An assertion is a new feature introduced in XSD 1.1 that allows you to specify any validation rules represented as XPath expressions on XML documents.

Here is the syntax on how an assertion rule should be defined in XSD schema:

 <xs:complexType name="type" ...>
  ...
  <xs:assert test="xpath_expression"/>
 </xs:complexType>

 <xs:simpleType name="type" ...>
  </xs:restriction>
   ...
   <xs:assertion test="xpath_expression"/>
  </xs:restriction>
 </xs:simpleType>

Note that:

Assertion should be applied to user defined datatype declared as "complexType" or "simpleType".
If an assertion is applied to a "complexType" datatype, assertion rules are declared as "assert" statements and placed inside the "complexType" statement at the end.
If an assertion is applied to a "simpleType" datatype, assertion rules are declared as "assertion" statements and placed inside the "restriction" statement at the end.
"assert[@test]" is required to provide an XPath expression, which must be evaluated to "true" for the XML document to be valid.

For example, the following assertion applies to a "complexType" datatype. It specifies that the "min" attribute value must be less or equal to the "max" attribute value:

<xs:complexType name="intRange">
 <xs:attribute name="min" type="xs:int"/>
 <xs:attribute name="max" type="xs:int"/>
 <xs:assert test="@min le @max"/>
</xs:complexType>

For example, the following assertion applies to a "simpleType" datatype. It specifies that the value must starts with number "4":

<xs:simpleType name="visaNumber">
  <xs:restriction base="xs:string">
    <xs:maxLength value="16"/>
    <xs:assert test="fn:starts-with($value, '4')"/>
  </xs:restriction>
</xs:simpleType>

Last update: 2014.

Table of Contents

About This Book

Introduction to XML Schema

XML Editor and Schema Processor - XMLPad

Java API for XML Processing - JAXP

JAXP - XML Schema (XSD) Validation

Xerces2 Java Parser - Java API of XML Parsers

Using Xerces2 Java API

XML Schema Language - Basics

Introduction of XSD Built-in Datatypes

"string" and Its Derived Datatypes