Consider the following scenario:
请考虑以下情形:
I want to save elements and their attributes in a database, these elements extend from a common but abstract supertype called "PersistentElement". Now some of these elements all have a particular attribute, e.g. they all have a name, and all of these elements again share a common superelement named "NamedElement", which again is abstract. That leads to a schema/XSD looking like this: I
