Relational Database Management System - RDBMS - Why There Is A Great Demand?
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.
The information 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.