Before specifying a key for a class, you must specify its extent.

More Questions from Object-Oriented Database

• In ODL, you specify an operation using parentheses after its name.
• ODL supports the abstract keyword for classes and operations.
• The Object Model supports different literal types, but does not support atomic literals, collection literals, and structured literals.
• An attribute's value is always literal.
• A collection of literals or object types is called a bag.
• Literals do not have identifiers, and, therefore, cannot be individually referenced like objects.
• An attribute's value is either a literal or an object identifier.
• Database objects are almost always transient.
• The ODMG Object Model requires that a relationship be specified in both directions.
• An ordered collection of elements of the same type are called sets.

Discussion & Comments