The sequence element specifies an exact sequence of children elements.

Example

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

This says: "The child sequence 'my:name', 'my:address', 'my:ssn' must occur here."

You can use 'minOccurs' and 'maxOccurs' on sequences:

<xs:sequence maxOccurs="unbounded">
   <xs:element ref="my:name"/>
   <xs:element ref="my:address"/>
   <xs:element ref="my:ssn"/>
</xs:sequence>

This allows the sequence 'my:name', 'my:address', 'my:ssn' to repeat over and over again.