Database Reference
In-Depth Information
Rule 8: Physical Data Independence:
The system should isolate all application
programs (and end user accesses) from the physical structure of the database. Changes in
one should not affect the other.
Rule 9: Logical Data Independence:
The system should isolate all application
programs (and end user accesses) from the logical structure of the database. Changes in
one should not affect the other.
Rule 10: Integrity Independence:
Integrity constraints must be specified separately
from application programs and stored in the system catalog. It must be possible to change
such constraints as required, without effect on the applications that access the database.
Rule 11: Distribution Independence:
Existing applications should continue to
operate successfully when distributed versions of the DBMS are first introduced or
upgraded.
Rule 12: Nun-subversion:
If the system provides a low-level (record-at-a-time)
interface, then it should not be possible to use this interface to undermine or bypass
relational security or integrity constraints of the system.
9.2.3 Far Reaching Consequences
These constraints set a very high standard for relational DBMS (RDBMS) suites to
attain. In fact, for a considerable period of time, the industry did not see a product that
irrefutably met all of these requirements. On the other hand, many proposed products
have fallen by the wayside, due to failure to come close enough to the established
standards. With incremental improvements to products such as (but not only) DB2,
Oracle, Informix, and Sybase over several years, the industry can now boast of products
meeting these standards (but not without room for improvement). Chapters 16 - 20 take a
look at some of these products.
Is the benchmark too high for RDBMS products? Not at all. It defines an ideal that
software engineering firms can strive to attain. It also establishes a firm mathematical
basis for the relational model. In this regard, the work of Codd, Date, Fagin, and others
cannot be over applauded. To a certain extent, the standards have protected the
consuming public from rogue companies that might have tried to exploit us by marketing
inferior database products under false claim of them being relational. We have seen many
such attempts, but for the most part, they have not gone very far.
In the next two divisions of the text, you will discover a rather interesting
phenomenon: Many of the standards described in the revised benchmark for a RDBMS
have been implemented in SQL, the universal database language, and leading DBMS
products such as DB2, Oracle, Sybase, Informix, MS SQL Server, and MySQL. This is
comforting information.
