Rule 8: Physical Data Independence
Application programs and terminal activities remain logically unimpaired whenever any
changes are made in either storage representation or access methods. i.e. Users and programs are
not dependent on the physical structure of the database.
Rule 9: Logical Data Independence
Application programs and terminal activities remain logically unimpaired when
information-preserving changes of any kind that theoretically permit unimpairment are made to
the base tables. Users and Programs are independent of the logical structure of the database, i.e.
the logical structure of the data can evolve with minimal impact on the programs.
Rule 10: Integrity Independence
Integrity constraints specific to a particular relational database must be definable in the
relational data sublanguage and storable in the catalog, not in the application programs. A
minimum of the following two integrity constraints must be supported:
1. Entity integrity: No component of a primary key is allowed to have a null value.
2. Referential integrity: For each distinct non-null foreign key value in a relational database,
there must exist a matching primary key value from the same domain.
Rule 11: Distribution Independence
A relational DBMS has distribution independence. Distribution independence implies that
users should not have to be aware of whether a database is distributed. Applications should still
work in a distributed database (DDB).
Rule 12: Nonsubversion Rule
If a relational system has a low-level (single-record-at-a-time) language, that low-level
language cannot be used to subvert or bypass the integrity rules or constraints expressed in the
higher-level (multiple-records-at-a-time) relational language.
If there is a record at a time interface (e.g. via 3GL), Security and integrity of the database
must no be violated. There should be no backdoor to bypass the security imposed by the DBMS.
On the basis of the above rules, there is no fully relational DBMS available today.
Questions and Answers :
What is Pseudo Colomn ?
USER, UID, SYSDATE, ROWNUM, ROWID, NULL, AND LEVEL
How to Display output in PL/SQL ?
we first
set serveroutput on
at SQL Prompt. and then in sql programming we specify as
dbms_output.put_line(`hdjhd' || `sakdha');
No Displays are allowed in PL/SQL programming with select statement
Write about Commands and Keywords ?
Alter : ALTER TABLE EMP ADD .......... , MODIFY .......... ;
for a in 1..10 loop ........... end loop;
loop exit when a<1 .................. end loop;
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