Question

I’m trying to do some form of composition with restrictions in XML Schema.

I have a complexType that is reused in several other complexTypes. I want to specify that FieldA must be one value when PartialType is included in FullTypeA, and a different value when it’s included in FullTypeB.

<xs:complexType name="PartialType">
    <xs:sequence>
        <xs:element name="FieldA" type="xs:unsignedShort" />
        <xs:element name="FieldB" type="xs:unsignedShort" />
    </xs:sequence>
</xs:complexType>

<!-- FieldA must be 1 for FullTypeA-->
<xs:complexType name="FullTypeA">
    <xs:sequence>
        <xs:element ref="PartialType" />
        <xs:element name="FieldC" type="xs:unsignedShort" />
    </xs:sequence>
</xs:complexType>

<!-- FieldA must be 2 for FullTypeB-->
<xs:complexType name="FullTypeB">
    <xs:sequence>
        <xs:element ref="PartialType" />
        <xs:element name="FieldD" type="xs:unsignedShort" />
    </xs:sequence>
</xs:complexType>

How should I structure my XML Schema to accommodate this scenario?

Answer 1

I think Xsd doesn’t really allow this.

One possible way to achieve this would be using xs:restriction

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:complexType name="PartialType">
        <xs:sequence>
            <xs:element name="FieldA" type="xs:unsignedShort" />
            <xs:element name="FieldB" type="xs:unsignedShort" />
            <xs:choice>
                <xs:element name="FieldC" type="xs:unsignedShort" />
                <xs:element name="FieldD" type="xs:unsignedShort" />
            </xs:choice>
        </xs:sequence>
    </xs:complexType>

    <xs:complexType name="FullTypeA">
        <xs:complexContent>
            <xs:restriction base="PartialType">
                <xs:sequence>
                    <xs:element name="FieldA" type="xs:unsignedShort" fixed="1" />
                    <xs:element name="FieldB" type="xs:unsignedShort" />
                    <xs:element name="FieldC" type="xs:unsignedShort" />
                </xs:sequence>
            </xs:restriction>
        </xs:complexContent>
    </xs:complexType>

    <xs:complexType name="FullTypeB">
        <xs:complexContent>
            <xs:restriction base="PartialType">
                <xs:sequence>
                    <xs:element name="FieldA" type="xs:unsignedShort" fixed="2" />
                    <xs:element name="FieldB" type="xs:unsignedShort" />
                    <xs:element name="FieldD" type="xs:unsignedShort" />
                </xs:sequence>
            </xs:restriction>
        </xs:complexContent>
    </xs:complexType>

</xs:schema>

The downside to this is obvious: You’ll have to declare all elements in your PartialType.

An alternative would be to use xs:extension

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:complexType name="PartialType">
        <xs:sequence>
            <xs:element name="FieldB" type="xs:unsignedShort" />
        </xs:sequence>
    </xs:complexType>

    <xs:complexType name="FullTypeA">
        <xs:complexContent>
            <xs:extension base="PartialType">
                <xs:sequence>
                    <xs:element name="FieldA" type="xs:unsignedShort" fixed="1" />
                    <xs:element name="FieldB" type="xs:unsignedShort" />
                    <xs:element name="FieldC" type="xs:unsignedShort" />
                </xs:sequence>
            </xs:extension>
        </xs:complexContent>
    </xs:complexType>

    <xs:complexType name="FullTypeB">
        <xs:complexContent>
            <xs:extension base="PartialType">
                <xs:sequence>
                    <xs:element name="FieldA" type="xs:unsignedShort" fixed="2" />
                    <xs:element name="FieldB" type="xs:unsignedShort" />
                    <xs:element name="FieldD" type="xs:unsignedShort" />
                </xs:sequence>
            </xs:extension>
        </xs:complexContent>
    </xs:complexType>

</xs:schema>