Making CORBA Objects Persistent: the Object Database Adapter Approach

This paper discusses a realization of object persistence in a CORBA-based distributed system. In our approach, persistence of CORBA objects is accomplished by the integration of the ORB with an ODBMS. This approach is not limited to pure object-oriented database systems, as the ODBMS may be a combination of a relational DBMS and an object-relational mapper. The design and implementation of an Object Database Adapter that integrates an ORB and an ODBMS with C++ bindings is presented. The ODA uses delegation (rather than inheritance) to connect user-provided implementation classes and IDL-generated classes. Only the user-defined parts of CORBA objects are actually stored in a database. Their IDL-generated parts are dynamically instantiated, in transient memory, by the ODA. Persistent relationships between CORBA objects within a server are not realized at the CORBA level, but at the level of implementation objects. Database traversals and queries can therefore be executed at ODBMS speeds. The paper discusses in some detail a number of implementation issues, such as caching. ODA support to local transactions, ODA interfaces, and CORBA server organization are also examined.