The difference between and in XSD?

Question

What is the difference between <all> <sequence> <choice> and <group> in XML Schema?

Answer 1

When to use xsd:all, xsd:sequence, xsd:choice, or xsd:group:

• Use xsd:all when all child elements must be present, independent of order.
• Use xsd:sequence when child elements must be present per their occurrence constraints and order does matters.
• Use xsd:choice when one of the child element must be present.
• Use xsd:group as a way to wrap any of the above in order to name and reuse in multiple locations within an XSD.

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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>

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See also

• Meaning of minOccurs and maxOccurs for xsd:choice?
• How do I make a group of elements all optional in an XSD (ie. minOccurs="0")?
• XML Schema minOccurs / maxOccurs default values