XML symbols

HMD trees express cardinality concepts using { }, [ ], and {[ ]}. These symbols do not map well to the XML cardinality designators ?, *, and +.

These symbols are used in XML trees:

  • ?

    This indicates "zero or one instance."

  • *

    This indicates "zero or more instances."

  • +

    This indicates "one or more instances."

  • ,

    This indicates "must follow."

  • |

    This indicates "either/or."

The XML tree uses "anonymous group" nodes that contain and express these relationships between child nodes.