A relational database
is a shared repository of data. A database management system is essentially
a collection of interrelated data and set of programs to access this
data. This collection of data is called a database. Relational database
can be used to represent complex relationships among datas as
well as to retrieve and update related data easily and efficiently.
Database systems support single as well as multi-user environments.
In case of DBMS only one user can access the database at the same time
Example: FoxPro, but in relational database management system more than
one user can access the database at the same time Example: unify, focus,
Sybase, Informix. If any DBMS satisfies Codd twelve rules and it should
satisfy relational theory in algebra then the database is called relational
database management system.
Since it maintains interrelationship among the datas present in
the database, data integrity, and provides a multi user environment
it is referred as RDMS. To qualify a genuine RDBMS, the system should
possess some inherent properties. (a) It must store data as a relation
that each column is independently identifies by its column name and
the ordering of rows is immaterial. (b) The operations available to
he user, as well as those internally used by the system, should be true
relational operations, that is they should be capable of generating
new relation from the old relations.
system will allow multiple users to access the database at the same
time and sharing of data is possible. The relational database must provide
with concurrency control software to ensure or avoids that several users
trying to update the same data at the same time, it should maintain
in a controlled manner. Relational model uses a collection of tables
to represent both data and relationships among those data. Data redundancy
is avoided that is storing of datas multiple times which result
in wastage of space, this may result in data inconsistency in the application.
Moreover in database approach multiple views can be created. View is
also called as Virtual table because view does not contain
physically stored records and will not occupy any space. Security is
one of the important aspects of RDBMS, the mechanism is used to prevent
destructive interaction of different users accessing the unauthorized
datas. Relational system provides us with locks to avoid or prevents
unauthorized by different users. Normalization helps is avoiding data
redundancy and preserves data integrity. During the process of normalization,
dependencies can be identified easily. Normalization theory is based
on the functional notion of functional dependency and moreover it helps
in simplifying the structure of tables.
A multi-user database
whose users have variety of applications must provide facilities for
defining multiple views. The structure of the database is stored separately
in the system catalog from the access of the application programs. This
property is known as program-data independence. It is possible to define
and enforce integrity constraints for the datas stored in the
database. The database also provides facilities for recovering hardware
and software failures. The backup recovery subsystem of the RDBMS is
responsible for recovery of datas, it also ensures that the program
is resumed from the point at which it is interrupted so that its full
effect is recorded in the database. It requires only limited time to
develop an application.
stored in the relational database must be stored in the row and column
format that is table format. Moreover every data item present in the
database will be logically addressable by a table name, column name
or by a primary key value. Any RDBMS should support systematic treatment
of null values. It should support data definition, data manipulation
and transaction management, and integrity constraints. And the information
present in one database should be possible to distribute to different
databases. Physical and logical structure of the databases should remain
unaffected even though any changes are done in physical or in the logical
level of the databases. The different levels in system should not revert
or bypass the integrity rules and constraints. The integrity constraints
should be stored in the system catalog of the database.