The choice element specifies an set of choices.

Example

<xs:choice>
   <xs:element ref="my:name"/>
   <xs:element ref="my:address"/>
   <xs:element ref="my:ssn"/>
</xs:choice>

This says: "Either 'my:name', 'my:address', or 'my:ssn' must occur here but not more than one."

You can use 'minOccurs' and 'maxOccurs' on choices.