XML Schema with a combination of choice and all - xsd

Question

I want to do the validations like:
<A>
<B> or <C>
<D>
</A>
In the , the first element should be one of the B and C. The second element is D. And at the same time, the first element B or C and the second element do not in sequence. It could become and . Anybody know how to do it?

Answer 1

To match your example, please try:
<?xml version="1.0" encoding="UTF-8" ?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="A">
<xs:complexType>
<xs:sequence>
<xs:choice>
<xs:element name="B" type="xs:string"/>
<xs:element name="C" type="xs:string"/>
</xs:choice>
<xs:element name="D" type="xs:string" minOccurs="0" maxOccurs="1" />
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
You have to use two things here, the first one is <xs:choice> which allows only one elements to be present in xml.
In order to make an element optional (D) you have to specify minOccurs="0".
Edited (after feedback): All valid cases are covered with this XSD.
<?xml version="1.0" encoding="UTF-8" ?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="B" type="xs:string"/>
<xs:element name="C" type="xs:string"/>
<xs:element name="D" type="xs:string"/>
<xs:complexType name="OurType">
<xs:choice>
<xs:sequence>
<xs:element ref="D"/>
<xs:choice>
<xs:element ref="B"/>
<xs:element ref="C"/>
</xs:choice>
</xs:sequence>
<xs:sequence>
<xs:choice>
<xs:element ref="B"/>
<xs:element ref="C"/>
</xs:choice>
<xs:element ref="D"/>
</xs:sequence>
</xs:choice>
</xs:complexType>
<xs:element name="A" type="OurType"/>
</xs:schema>

Answer 2

I get the best practice. It should be as below:
<xs:element name="A">
<xs:complexType>
<xs:all>
<xs:element ref="Choice" minOccurs="1" maxOccurs="1"/>
<xs:element ref="D" minOccurs="0" maxOccurs="1"/>
</xs:all>
</xs:complexType>
</xs:element>
<xs:element name="D" type="xs:string"/>
<xs:element name="Choice" abstract="true"/>
<xs:element name="B" substitutionGroup="Choice">
</xs:element>
<xs:element name="C" substitutionGroup="Choice">
</xs:element>