ypes (integer, real, char, string). This set should be extensible i.e. the user should be able to define his/her own types and treat them in the same way he/she treats the predefined ones. In other words, user types and system types should have the same status although perhaps they are differently supported by the system itself.Persistence is one of the most basic features of a DBMS (at least the most evident one) and hence of an OODBMS. It is the ability of the programmer to have his/her own data survive the execution of a process so that he/she can eventually reuse it in another process. For an object-oriented system, there is an additional requirement which stems from the extensibility requirement, 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 should include 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 databases should be able to choose if he/she will activate these mechanisms or not, although for application programmers the use of these mechanisms should be transparent and not require special effort for their maintenance.The database management system should be able to support many users. That means that they must provide special mechanisms for the concurrency of the accesses of the data, and the arbitration in case of conflicts. Such mechanisms have already been provided by the RDBMSs and hence should also be provided by the OODBMSs. A basic requirement for a database system is that in case of a hardware or software failure, the system should be able to bring itself back to the most recent coherent state of the data. This feature has to do with the concurrency control and the transaction management, but also requires extra mechanisms that have already been explored and studied for the RDBMSs.A DBMS should pro...
