Assertion as the Forth Level Constraints
This section describes validation rules specified as assertions, which can be viewed as the forth level of constraints that you can force the XML document author to comply.
Validation rules specified as assertions
can be viewed as the forth level of constraints that you can force
the XML document author to comply:
- First Level Constraints - XSD built-in datatypes applied on attributes and simple element contents.
- Second Level Constraints - User-defined datatypes applied on complex elements.
- Third Level Constraints - Identify constraints applied on repeating sub elements.
- Forth Level Constraints - Assertion validation rules applied across attributes and/or elements.
For example, I receive an order XML message, order.xml, from a client system asking to price the order:
- Copyright (c) 2014, HerongYang.com, All Rights Reserved.
<line sku="XMLBOOK" quantity="1.0"/>
<line sku="XMLBOOK" quantity="2"/>
Obviously, there are a number of areas in this order XML message
that we can use XSD schema to improve the quality:
- quantity="1.0" - The quantity should be a positive integer number.
We can use first level constraints like the XSD built-in datatype "positiveInteger" to enforce this rule.
- billto country="CA" - The "billto" sub element should be placed before all "line" sub elements.
We can use second level constraints like defining our own complex element type to enforce the sequence
of sub elements.
- sku="XMLBOOK" - Any two order lines should not have the same SKU number.
We can use third level constraints like defining a key identify constraint to enforce "sku" values
to be unique.
- currency="USD" and country="CA" - The currency "USD" should not be used in bill-to country "CA.
We can use forth level constraints like defining a validation assertion to enforce "currency" values
to be valid in the bill-to country.
The validation assertion could be expressed in XPath as
"(billto/@country eq 'CA' and @currency eq 'CAD')
or (billto/@country eq 'US' and @currency eq 'USD')".
See the next section for the full XSD schema.
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
"decimal" and Its Derived Datatypes
"dateTime" and Its Related Datatypes
Miscellaneous Built-in Datatypes
Facets, Constraining Facets and Restriction Datatypes
"simpleType" - Defining Your Own Simple Datatypes
Complex Element Declaration
Identity-Constraints: unique, key and keyref
►Assertion as Custom Validation Rules
What Is an Assertion?
►Assertion as the Forth Level Constraints
"assert" Statements for "complexType" Datatype
"assertion" Statements for "simpleType" Datatype
XML Schema Location and Namespace in XML Documents
Overriding Element Types in XML Documents
Linking Multiple Schema Documents Together
PDF Printing Version