We put under this heading things which clearly improve the system, but which are not mandatory to make it an object-oriented database system.
Some of these features are of an object oriented nature (e.g. multiple inheritance). They are included in this category because, even though they make the system more object-oriented, they do not belong in the core requirements.
Other features are simply database features (e.g. design transaction management). These characteristics usually improve the functionality of a data base system, but they are not in the core requirement of database systems and they are unrelated to the object oriented aspect. In fact most of them are targeted at serving ``new'' applications (CAD/CAM, CASE, Office automation, etc.) and are more application oriented than technology oriented. Because many object-oriented database systems are currently aiming at these new applications, there has been some confusion between these features and the object-oriented nature of the system.