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.