Currently, the SQL OS does not persist properties of super-classes when a polymorphic class is persisted. Additionally, abstract classes and interfaces are treated the same as concrete classes.
There are two obvious options:
1) The persisted polymorphic class creates a row in an uber-table of concatenated properties of all super-classes.
2) The persisted polymorphic class creates rows in each table that corresponds to a super-class (the concrete sub-class is contained in multiple tables, 1 per super-class).