A locking protocol for object-oriented database systems (OODBSs) is presented. The protocol can exploit the semantics of methods invoked on encapsulated objects. Compared to conventional page-oriented or record-oriented concurrency control protocols, the proposed protocol greatly improves the possible concurrency because commutative method executions on the same object are not considered as a conflict. An OODBS application example is presented. The principle of open-nested transactions is reviewed. It is shown that, using the locking protocol in an open-nested transaction, the locks of a subtransaction are released when the subtransaction completes, and only a semantic lock is held further by the parent of the subtransaction.>

VODAK is a prototype of an object-oriented, distributed database system developed during the past five years at the Integrated Publication and Information Systems Institute (IPSI). The aim of demonstrating VODAK Open Nested Transactions is to provide insights into internals of database systems that are usually hidden from application programmers and users. By utilizing semantics of methods, VODAK Open Nested Transactions increase the degree of parallelism between concurrent transactions compared to conventional transaction management schemes. Demonstrating the difference in parallelism provides users with a “feeling” for internal database mechanisms, application programmers with information about the impact of transaction management on performance, and system developers with ideas how to improve their systems with respect to transaction management.

The V3 Video Server is a demonstration showing a multimedia application developed on top of the VODAK database management system. VODAK is a prototype of an object-oriented and distributed database management system (DBMS) developed at GMD-IPSI. The V3 Video Server allows a user to interactively store, retrieve, manipulate, and present analog and short digital video clips. A video clip consists of a sequence of pictures and corresponding sound. Several attributes like author, title, and a set of keywords are annotated. The highlights of the demonstration are as follows. (1) It is shown that an object-oriented database management systems is very useful for the development of multimedia applications. (2) The video server gives valuable hints for the development of an object-oriented database management system in direction to a multimedia database management system.

A systematic discussion of atomic commitment for heterogeneous database systems is presented. An analysis is given of two alternative protocols for atomic commitment: commitment of local transaction after or before the global commit or abort decision is made. The impact of the protocols on recovery and concurrency control is shown. Atomicity, consistency, isolation, and durability properties are achieved for global transactions. It is demonstrated that commitment before fits best to multilevel transactions. In this case, the commitment protocol causes no additional overhead and a higher degree of concurrency can be achieved.>

In an object-oriented database the objects are encapsulated, that is, objects are only accessible by methods defined in the database system. The definition of object-oriented serializability takes advantage of the semantics and of the nesting of the methods. Therefore, a lower rate of conflicting accesses than with the conventional definition of serializability is achieved. Transactions of an object-oriented database are defined as open-nested transactions. Depending on the semantics of operations, actions can be serialized independently of the calling transactions. The techniques already used in multilayer transaction systems are extended to object-oriented systems. Object-oriented serializability includes multilayer serializability but allows a nonlayered, more general structure of the database system.>