"assertion" Statements for "simpleType" Datatype

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

XSD Tutorials - Herong's Tutorial Examples

∟"assertion" Statements for "simpleType" Datatype

This section provides a tutorial example on how to use 'assertion' statements for 'simpleType' custom defined datatypes.

When using assertion validation rules on "simpleType" custom defined datatypes, we need to remember several things:

Use "assertion", not "assert", statements inside the "restriction" statement at the end.
Use "$value" in the XPath expression to represent the value of the node that is being validated.
Use "xxx()" in the XPath expression to invoke built-in functions to construct complex expressions.

Here is an example of an XSD 1.1 schema, visa_card, that defines an assertion validation rule for a "simpleType" custom defined datatype:

<?xml version="1.0"?>
<!-- visa_card.xsd
 - Copyright (c) 2014, HerongYang.com, All Rights Reserved.
-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
 <xs:element name="visaCard" type="visaCardType"/>

 <xs:complexType name="visaCardType">
  <xs:sequence>
   <xs:element name="number" type="visaNumber"/>
   <xs:element name="name" type="xs:string"/>
  </xs:sequence>
 </xs:complexType>

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

</xs:schema>

This XSD schema enforces the XML document to provide a Visa number starting with digit "4". Here is a sample XML document, visa_card.xml, that should fail the XSD schema validation:

<?xml version="1.0"?>
<!-- visa_card.xml
 - Copyright (c) 2014, HerongYang.com, All Rights Reserved.
-->
<visaCard>
 <number>5454545454545454</number>
 <name>John Gates</name>
</visaCard>

Again, let's use the "jaxp.TypeInfoWriter" sample program from Xerces2 to validate the XML document:

>jdk8x2r jaxp.TypeInfoWriter -xsd11 -a visa_card.xsd -i visa_card.xml

setDocumentLocator(systemId="file:///C:/herong/visa_card.xml", pub...
startDocument()
 startElement(name="visaCard",type="visaCardType",attributes={})
  startElement(name="number",type="visaNumber",attributes={})
  
[Error] visa_card.xml:6:35: cvc-assertion.3.13.4.1: Assertion
^^^ evaluation ('starts-with($value, '4')') for element 'number' with
^^^ type 'visaNumber' did not succeed.

  endElement(name="number")
  startElement(name="name",type="{http://www.w3.org/2001/XMLSchema...
  endElement(name="name")
 endElement(name="visaCard")
endDocument()

The error message confirms that the "assertion" statement in visa_card.xsd is working.

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