Trong các giao dịch phân phối, có yêu cầu bổ sung cho một giao thức để đảm bảo rằng tất cả các máy chủ có liên quan trong giao dịch đồng ý hoặc tất cả các cam kết hoặc tất cả các hủy bỏ. Khuôn khổ cơ bản để xây dựng các giao thức như vậy sẽ liên quan đến | Component Database Systems 431 performance of new components might not be possible . specialized concurrency control for new index structures . As for the latter point more research is needed to fully understand the implications and side effects of CDBMSs. The work conducted in the area of CDBMSs has focused on extensions in the area of new data types including indexes useful for those nonstandard types . Componentization of the DBMS kernel including the transaction manager and the query processor in general and the optimizer in particular has been considered less thoroughly so far. In those areas a better understanding of the implications and limitations of componentization is necessary. It might turn out that subsystems also need to be componentized and that it might be possible to specialize them by adding or replacing new sub components. Despite the problems that still need to be addressed component DBMSs will certainly gain practical significance and componentization of DBMSs will continue to be a major trend in DB technology. References 1 Date C. J. and H. Darwen A Guide to the SQL Standard 4th ed. Reading MA Addison-Wesley 1997. 2 Bernstein P. A. V. Hadzilacos and N. Goodman Concurrency Control and Recovery in Database Systems Reading MA Addison-Wesley 1987. 3 Codd E. A Relational Model for Large Shared Data Banks Comm. ACM Vol. 13 No. 6 1970. 4 Atkinson M. P. et al. The Object-Oriented Database System Manifesto A Political Pamphlet Proc. 1st Intl. Conf on Deductive and Object-Oriented Databases Kyoto Japan Dec. 1989. 5 Cattell R. G. G. and D. Barry eds. The Object Database Standard ODMG San Francisco CA Morgan Kaufmann 1997. 6 Vaskevitch D. Database in Crisis and Transition A Technical Agenda for the Year 2001 Proc. ACM-SIGMOD Intl. Conf on Management of Data Minneapolis MN May 1994. 7 Sheth A. P. and J. A. Larson Federated Database Systems for Managing Distributed Heterogeneous and Autonomous Databases ACM Computing Surveys Vol. 22 No. 3 Sept. 1990.
