hould be able to define his/her own types and treatthem in the same way he/she treats the predefined ones. In other words, user types andsystem types should have the same status although perhaps they are differently supportedby the system itself.Persistence is one of the most basic features of a DBMS (at least the most evident one) andhence of an OODBMS. It is the ability of the programmer to have his/her own data survive theexecution of a process so that he/she can eventually reuse it in another process. For anobject-oriented system, there is an additional requirement which stems from the extensibilityrequirement, that any object must be able to become persistent independently of its type.The secondary storage management is one of the most important DBMS features. It shouldinclude a set of mechanisms that improve the performance of the system like indexing,clustering, access path selection, data buffering, or caching. The designer of the databasesshould be able to choose if he/she will activate these mechanisms or not, although forapplication programmers the use of these mechanisms should be transparent and not requirespecial effort for their maintenance.The database management system should be able to support many users. That means thatthey must provide special mechanisms for the concurrency of the accesses of the data, andthe arbitration in case of conflicts. Such mechanisms have already been provided by theRDBMSs and hence should also be provided by the OODBMSs. A basic requirement for adatabase system is that in case of a hardware or software failure, the system should be ableto bring itself back to the most recent coherent state of the data. This feature has to do withthe concurrency control and the transaction management, but also requires extra mechanismsthat have already been explored and studied for the RDBMSs.A DBMS should provide its users with a simple interactive way of making ad-hoc queries andreceiving answers. For this ...
