Can XSD choice be empty?

Question

I've read the XSD specification but I'm still confused. Is an empty choice valid in XSD? I mean, with a simple choice with no attributes declared, is mandatory to have either element "a" or element "b", or can it be empty?

<xs:complexType name="ChoiceType">
    <xs:choice>
        <xs:element name="a" type="type_a"/>
        <xs:element name="b" type="type_b"/>
    </xs:choice>
</xs:complexType>

Answer 1

Yes, the element governed by an xsd:choice can be empty, if minOccurs="0" is used:

• minOccurs="0" can be on the xsd:choice itself.
• minOccurs="0" can be on all of the children.

Related answer: An xsd:choice itself can be empty and would indicate that the element being defined must be empty.

Finally, note that in your example, no, one of a or b must be present because the default for minOccurs is 1.