Static data members are allowed but not stored in the database. However, a non-persistent capable class can be embedded. Persistent objects are created using an overloaded version of the new operator that specifies the database or other clustering information. A NULL database corresponds to a transient object. Objectivity claims that their persistent new and delete are faster than the transient ones if the database is not updated.
Associations are an alternative to object references.
ODMG-93 defines a set of collection and container classes. I don't know whether this is currently v6 or v7. The .hh file for persistent capable classes is no longer the primary definition of the class interface. This has implications for code generation from CASE Tools. An ODL compiler is available from an Objectivity distributor.