Difference between group and sequence in XML Schema?

Question

What is the difference between an xs:group and an xs:sequence in XML Schema? When would you use one or the other?

Answer 1

xs:sequence - together with xs:choice and xs:all - is used to define the valid sequences of XML element in the target XML. E.g. the schema for this XML:

<mainElement>   <firstSubElement/>   <subElementA/>   <subElementB/> </mainElement> 

is something like:

<xs:element name='mainElement'>   <xs:complexType>     <xs:sequence>       <xs:element name="firstSubElement"/>       <xs:element name="subElementA"/>       <xs:element name="subElementB"/>     </xs:sequence>   </xs:complexType> </xs:element> 

xs:group is used to define a named group of XML element following certain rules that can then be referenced in different parts of the schema. For example if the XML is:

<root>    <mainElementA>     <firstSubElement/>     <subElementA/>     <subElementB/>   </mainElementA>    <mainElementB>     <otherSubElement/>     <subElementA/>     <subElementB/>   </mainElementB>  </root> 

you can define a group for the common sub-elements:

<xs:group name="subElements">   <xs:sequence>     <xs:element name="subElementA"/>     <xs:element name="subElementB"/>   </xs:sequence> </xs:group> 

and then use it:

  <xs:element name="mainElementA">     <xs:complexType>       <xs:sequence>         <xs:element name="firstSubElement"/>         <xs:group ref="subElements"/>       </xs:sequence>     </xs:complexType>   </xs:element>    <xs:element name="mainElementB">     <xs:complexType>       <xs:sequence>         <xs:element name="otherSubElement"/>         <xs:group ref="subElements"/>       </xs:sequence>     </xs:complexType>   </xs:element>