XML in a Nutshell, 3rd Edition

Name

xsi:type

Synopsis

The xsi:type attribute may be used in instance documents to indicate the type of an element, even when a full schema is not available. For example, this length element has type xs:decimal:

<length xsi:type="xs:decimal">23.5</length>

More importantly, the xsi:type attribute enables a limited form of polymorphism. That is, it allows you to make an element an instance of a derived type where an instance of the base type would normally be expected. The instance of the derived type must carry an xsi:type attribute identifying it as an instance of the derived type.

For example, suppose a schema says that a ticket element has type TicketType. If the schema also defines BusTicketType and AirplaneTicketType elements as subtypes of TicketType, then a ticket element could also use the BusTicketType and AirplaneTicketType content models provided it had an xsi:type="BusTicketType" or xsi:type="AirplaneTicketType" attribute.