Question 1 :
ODL supports the abstract keyword for classes and operations.
Question 2 :
The ODMG Object Model requires that a relationship be specified in both directions.
Question 3 :
Before specifying a key for a class, you must specify its extent.
Question 4 :
The Object Model supports different literal types, but does not support atomic literals, collection literals, and structured literals.
Question 5 :
The ODMG Object Model supports only unary and binary relationships.