Schema Tutorial

The schema below defines three elements: "C", "D", "E". The elements "D" and "E" have the attribute "substitutionGroup" set to "C" (so they should be able to substitute the element "C"). But only element "E" can, because the type of element "D" is derived by an extension from the type "AAA" and this would be in conflict with the "block" attribute of element "C" (it has value "extension"). 3.3.6 Constraints on Element Declaration Schema Components; Schema Component Constraint: Substitution Group OK (Transitive)

Valid document

Invalid document
Because the type of the element "D" is created by an extension from type "AAA" and "AAA" is the type of "C" element and "C" element is defined with attribute "block" set to "extension", the document is not valid.

Valid document
Document is valid, because the type of the "E" element is not created by an extension from the type "AAA" and substitutions are allowed.

Correct XML Schema (correct_0.xsd)

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" >

  <xsd:element name="root">
    <xsd:complexType>
      <xsd:sequence minOccurs="1">
        <xsd:element ref="C"/>
      </xsd:sequence>
    </xsd:complexType>
  </xsd:element>

  <xsd:complexType name="AAA">
    <xsd:simpleContent>
      <xsd:extension base="xsd:integer"/>
    </xsd:simpleContent>
  </xsd:complexType>

  <xsd:element name="C" type="AAA" block="extension"/>

  <xsd:element name="D" substitutionGroup="C">
    <xsd:complexType>
      <xsd:simpleContent>
        <xsd:extension base="AAA">
          <xsd:attribute name="bbb" type="xsd:string"/>
        </xsd:extension>
      </xsd:simpleContent>
    </xsd:complexType>
  </xsd:element>

  <xsd:element name="E" type="AAA" substitutionGroup="C"/>
</xsd:schema>

Attribute block set to "extension"

1. XML Schema