"ID" Datatype Values and Representations

XSD Tutorials - Herong's Tutorial Examples

∟"ID" Datatype Values and Representations

This section describes the built-in datatype 'ID' designed to primarily support the id attribute to identify a specific XML element. 'ID' values must be 'NCName' values and must be unique in a single XML document.

The second datatype derived from "NCName" is "ID, which is designed to primarily support values used in the id attribute to identify a specific XML element.

"ID" is a datatype derived from "NCName" datatype with these rules:

A "ID" value must be "NCName" value.
"ID" values must be unique in an single XML document.
"ID" values are allowed to use as both element contents and attribute values.

Here is a sample XSD document that defines 2 sub element <IDElement> and <IDAttribute> to use "ID" values as element contents and as element attributes:

<?xml version="1.1"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<!-- ID_datatype_test.xsd
 - Copyright (c) 2002-2013 HerongYang.com. All Rights Reserved.
-->
<xs:element name="ID_Datatype_Test">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="ID_Element" type="xs:ID"
        maxOccurs="unbounded"/>
      <xs:element name="ID_Attribute" maxOccurs="unbounded">
        <xs:complexType>
          <xs:attribute name="ID" type="xs:ID"/>
        </xs:complexType>
      </xs:element>
    </xs:sequence>
  </xs:complexType>
</xs:element>
</xs:schema>

Here is a sample XML document to test these definitions:

<?xml version="1.1"?>
<!-- id_datatype_test.xml
 - Copyright (c) 2002-2013 HerongYang.com. All Rights Reserved.
-->
<ID_Datatype_Test>
<!-- 3 valid "ID" values as element contents -->
  <ID_Element>    site-logo </ID_Element>
  <ID_Element>  cover.photo </ID_Element>
  <ID_Element>  stdin       </ID_Element>

<!-- 3 invalid "ID" values as element contents -->
  <ID_Element>site-logo </ID_Element>
  <ID_Element>  2835c0d60046c109    </ID_Element>
  <ID_Element>  std:out     </ID_Element>

<!-- 3 valid "ID" values as attribute values -->
  <ID_Attribute ID=" top.left   "/>
  <ID_Attribute ID="    First_Signature  "/>
  <ID_Attribute ID=" Item123   "/>

<!-- 1 invalid "ID" values as attribute values -->
  <ID_Attribute ID=" stdin   "/>
</ID_Datatype_Test>

Here is the output of the JDK tool XsdSchemaValidator.java on this test. It is reporing 4 groups of errors for those 4 invalid elements.

herong> java XsdSchemaValidator
^^^ id_datatype_test.xsd id_datatype_test.xml

Error:
   Line number: 13
   Column number: 36
   Message: cvc-id.2: There are multiple occurrences of ID value
   'site-logo'.

Error:
   Line number: 13
   Column number: 36
   Message: cvc-type.3.1.3: The value 'site-logo ' of element
   'ID_Element' is not valid.

Error:
   Line number: 14
   Column number: 48
   Message: cvc-datatype-valid.1.2.1: '2835c0d60046c109' is not a
   valid value for 'NCName'.

Error:
   Line number: 14
   Column number: 48
   Message: cvc-type.3.1.3: The value '  2835c0d60046c109    ' of
   element 'ID_Element' is not valid.

Error:
   Line number: 15
   Column number: 40
   Message: cvc-datatype-valid.1.2.1: 'std:out' is not a valid value
   for 'NCName'.

Error:
   Line number: 15
   Column number: 40
   Message: cvc-type.3.1.3: The value '  std:out     ' of element
   'ID_Element' is not valid.

Error:
   Line number: 23
   Column number: 32
   Message: cvc-id.2: There are multiple occurrences of ID value
   'stdin'.

Error:
   Line number: 23
   Column number: 32
   Message: cvc-attribute.3: The value ' stdin   ' of attribute
   'ID' on element 'ID_Attribute' is not valid with respect to its
   type, 'ID'.

Failed with errors: 8