reference other element in the same xml file

[carlgmt]

\[code\]<data> <parent1> <name> <age> ... </parent1> <parent2> <name> <age> ... </parent2> <children> <child1> <content>....</content> <ref parent1> <ref parent2> </child1> <child2> <content>...</content> <ref parent1> </child2> <children></data>\[/code\]I want to have the child reference the parent instead of copy the parent to all child. what's the right way to ref the parent element from the child? if I parse the file, the parser can see the parent element as already copied to ref place?