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Complex Type Derivation Using the Extension Mechanism

  • Artigo

A complex type derived by extension is a functional superset of its base data type. As the name implies, its base data type is the basis for the type being defined, where the differences from the base type are additive. This topic provides an example in which the two elements ShippingAddress and BillingAddress are based on the complex global type GlobalAddrType. ShippingAddress is simply defined to be of type GlobalAddrType, whereas BillingAddress is defined to extend the type GlobalAddrType. At the end of the example, an additional element is added to BillingAddress, named Department, with a type of string and a default value of Accounts Payable.

For comprehensive information about deriving new complex types by using the extension mechanism, refer to the W3C website. For various links to this and other websites, see XSD Resources on the Web.

To derive from a complex global type by extension, in another location in the schema tree, begin by inserting a new Record node at the desired location. Then set its Base Data Type property to the name of a complex global type.

In the following example, BillingAddress is the name of the newly inserted Record node, and GlobalAddrType is the name of the complex global type from which it derives, and intends to extend. In the schema tree view, after Base Data Type has been set to GlobalAddrType, a duplicate node structure would be displayed below the node named BillingAddress, identical to the adjacent node structure under the node named ShippingAddress. The difference between them is that the BillingAddress node structure will be extensible beyond the base data type GlobalAddrType, and the ShippingAddress structure will remain identical to the base data type GlobalAddrType.

  • Before, with a newly inserted node named BillingAddress.

    <xs:schema>  
    <xs:element name="Root">  
        <xs:complexType>  
            <xs:sequence>  
                <xs:element name="ShippingAddress" type="GlobalAddrType" />  
                <xs:element name="BillingAddress">  
                    <xs:sequence />  
                </xs:element>  
            </xs:sequence>  
        </xs:complexType>  
    </xs:element>  
    <xs:complexType name="GlobalAddrType">  
    [Address structure defined globally here.]  
    </xs:complexType>  
</xs:schema>

  • After deriving from the complex base type GlobalAddrType, by extension.

    <xs:schema>  
    <xs:element name="Root">  
        <xs:complexType>  
            <xs:sequence>  
                <xs:element name="ShippingAddress" type="GlobalAddrType" />  
                <xs:element name="BillingAddress">  
                    <xs:complexType>  
                        <xs:complexContent mixed="false">  
                            <xs:extension base="GlobalAddrType" />  
                        </xs:complexContent>  
                    </xs:complexType>  
                </xs:element>  
            </xs:sequence>  
        </xs:complexType>  
    </xs:element>  
    <xs:complexType name="GlobalAddrType">  
    [Address structure defined globally here.]   
    </xs:complexType>  
</xs:schema>

    You specify extensions to the base data type by inserting nodes into the BillingAddress node in the schema tree. The following XSD fragment shows how the empty extension element is expanded when a Sequence Group node is inserted as a new child of the BillingAddress node and then a Field Element node, named PaymentType, is inserted as a child node of the Sequence Group node.

<xs:extension base="GlobalAddrType">  
    <xs:sequence>  
        <xs:element default="Accounts Payable"  
            name="Department" type="xs:string" />  
    </xs:sequence>  
</xs:extension>

See Also

Complex Global Type Derivation