What is DBMS
A database is a very well organized collection of data so as to able to carry out operations like insertion, deletion, updation and retrieval. Thus, a database needs to be managed by an appropriate package of software which is called DBMS (Database Management System). The primary purpose of a DBMS which is basically a collection of programs is to allow a user to store, update, retrieve data and thus make it easy to maintain and retrieve information from a database. The DBMS relieves the use from knowing how the data is stored physically and complex algorithms used for performing operations on the database. It only concentrates on how the operations are to be performed to retrieve the data from the database. The DBMS is incharge of access, security, storage and host of other functions for the database system. It does this through a selection of computer system. This allows it to manage the large, structured sets of data, which makes up the database and provides access to the data for multiple, concurrent users while maintaining the integrity of the data. The DBMS provides security facilities in a variety of forms, both to prevent unauthorized access and to prevent authorized users from accessing the system, it uses passwords to identify operators, programs and individual machines and set of privileges assigned to them. These privileges can include the ability to read, write and update data in database. DBMS acts as an intermediate between the user and the database. The DBMS has advantages like:
Controls data redundancy Elimination of inconsistency Better service to the users Flexibility of the system is improved Integrity can be improved Standards can be enforced Security can be improved Data Independence
In addition to all these advantages it provides many other advantages too like provides backup and recovery etc. Disadvantages include:
Confidentiality, privacy and security is reduced Cost of using DBMS is high Threat to data integrity Enterprise vulnerability
DBMS has three level architecture. The three level architecture of DBMS includes three views of data which are External View which is available to the end user, Conceptual Level which is the middle level and represents all the database entities, their relationships and constraints on it and the third view is Internal Level which is the actual physical storage of data. It tells us how the data is stored physically in the database. The three levels of the DBMS are not independent of each other. There is correspondence between them and this is called as Mapping.