"ENTITY" Datatype Values and Representations

XSD Tutorials - Herong's Tutorial Examples - Version 5.10, by Dr. Herong Yang

XSD Tutorials - Herong's Tutorial Examples

∟"ENTITY" Datatype Values and Representations

This section describes the built-in datatype 'ENTITY' designed to support user defined and unparsed external XML entities. 'ENTITY' datatype is derived from 'NCName'.

In order to support some XML document special features, 3 built-in datatypes are derived from "NCName": "ENTITY", "ID" and "IDREF".

"ENTITY" is a datatype derived from "NCName" datatype by limiting its value to names of user defined unparsed external XML entities.

Note that XML entities can not be defined in XSD document. They must be defined in the DTD (Document Type Definition) format embedded in or assigned to the XML document. Here is an example of a DTD statement that defines an unparsed external XML entity called "site-logo":

<!ENTITY site-logo SYSTEM "logo.gif" NDATA gif>

Here is a sample XSD document that defines a sub element <ENTITY> to use "ENTITY" values:

<?xml version="1.1"?>
<!-- ENTITY_datatype_test.xsd
 - Copyright (c) 2013, HerongYang.com, All Rights Reserved.
-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="ENTITY_Datatype_Test">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="ENTITY" type="xs:ENTITY" 
        maxOccurs="unbounded"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>
</xs:schema>

Here is a sample XML document that contains <ENTITY> elements to test that definition:

<?xml version="1.1"?>
<!-- ENTITY_datatype_test.xml
 - Copyright (c) 2013, HerongYang.com, All Rights Reserved.
-->

<!DOCTYPE ENTITY_Datatype_Test [
  <!ENTITY site-logo SYSTEM "logo.gif" NDATA gif>
  <!ENTITY cover.photo SYSTEM "sunrise.jpg" NDATA jpeg>
  <!ENTITY stdin SYSTEM "input.dat" NDATA data>
  <!ENTITY std:out SYSTEM "output.dat" NDATA data>
  <!ENTITY footer SYSTEM "/boilerplate/footer.xml">
  <!ENTITY quot "&#x22;">
]>

<ENTITY_Datatype_Test>
<!-- 3 valid "ENTITY" elements -->
  <ENTITY>    site-logo </ENTITY>
  <ENTITY>  cover.photo </ENTITY>
  <ENTITY>  stdin       </ENTITY>

<!-- 5 valid "ENTITY" elements -->
  <ENTITY>  bg-image    </ENTITY>
  <ENTITY>  std:out     </ENTITY>
  <ENTITY>    footer    </ENTITY>
  <ENTITY>      quot    </ENTITY>
  <ENTITY>       amp    </ENTITY>
</ENTITY_Datatype_Test>

Notes on this example XML document, entity_datatype_test.xml:

A block of DTD statements is embedded in the document: <!DOCTYPE ENTITYDatatypeTest [...]>.
"bg-image" is not a valid ENTITY, because it is not a defined entity.
"std:out" is not a valid ENTITY, because it is not a valid "NCName" value. ":" is not allowed.
"footer" is not a valid ENTITY, because it is defined as a parsed external entity.
"quot" is not a valid ENTITY, because it is defined as a parsed internal entity.
"amp" is not a valid ENTITY, because it is a built-in parsed internal entity.

If you run JDK 1.7 tool XsdSchemaValidator.java on this test, you will see 5 groups of errors for the last 5 invalid elements.

c:\Progra~1\Java\jdk1.7.0_07\bin\java.exe XsdSchemaValidator 
   entity_datatype_test.xsd entity_datatype_test.xml

Error:
   Line number: 22
   Column number: 34
   Message: UndeclaredEntity: Entity 'bg-image' is not declared.

Error:
   Line number: 22
   Column number: 34
   Message: cvc-type.3.1.3: The value '  bg-image    ' of element 
   'ENTITY' is not valid.

Error:
   Line number: 23
   Column number: 34
   Message: cvc-datatype-valid.1.2.1: 'std:out' is not a valid value
   for 'NCName'.

Error:
   Line number: 23
   Column number: 34
   Message: cvc-type.3.1.3: The value '  std:out     ' of element 
   'ENTITY' is not valid.

Error:
   Line number: 24
   Column number: 34
   Message: UndeclaredEntity: Entity 'footer' is not declared.

Error:
   Line number: 24
   Column number: 34
   Message: cvc-type.3.1.3: The value '    footer    ' of element 
   'ENTITY' is not valid.

Error:
   Line number: 25
   Column number: 34
   Message: UndeclaredEntity: Entity 'quot' is not declared.

Error:
   Line number: 25
   Column number: 34
   Message: cvc-type.3.1.3: The value '      quot    ' of element 
   'ENTITY' is not valid.

Error:
   Line number: 26
   Column number: 34
   Message: UndeclaredEntity: Entity 'amp' is not declared.

Error:
   Line number: 26
   Column number: 34
   Message: cvc-type.3.1.3: The value '       amp    ' of element 
   'ENTITY' is not valid.

Failed with errors: 10

Note that you may have difficulties to validate this XML document with the XSD schema with other XML tools, because it has the embedded DTD statements.

Last update: 2013.

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