What is the difference between <all> <sequence> <choice> and <group> in XML Schema?
When to use xsd:all, xsd:sequence, xsd:choice, or xsd:group:
xsd:all when all child elements must be present, independent of
order.xsd:sequence when child elements must be present per their
occurrence constraints and order does matters.xsd:choice when one of the child element must be present.xsd:group as a way to wrap any of the above in order to name
and reuse in multiple locations within an XSD.Note that occurrence constraints can appear on xsd:all, xsd:sequence, or xsd:choice in addition to the child elements to achieve various cardinality effects.
For example, if minOccurs="0" were added to xsd:element children of xsd:all, element order would be insignificant, but not all child elements would have to be present:
<?xml version="1.0"?>
<xsd:schema elementFormDefault="qualified"
xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<xsd:element name="r">
<xsd:complexType>
<xsd:all>
<xsd:element name="a" type="xsd:string" minOccurs="0"/>
<xsd:element name="b" type="xsd:string" minOccurs="0"/>
<xsd:element name="c" type="xsd:string" minOccurs="0"/>
</xsd:all>
</xsd:complexType>
</xsd:element>
</xsd:schema>
For the above XSD, the following XML would be valid, even though not all children of r are present:
<r>
<b/>
<a/>
</r>