Database Management System

What is DBMS :
               DBMS is a software that helps in easy retrieval and managing the database. A database is a storage structure which contains tables. The tables will have records and attributes. Records are the row in the tables and Attributes are the column in the tables.

DBMS VS FILES :
           Files are common data storage where the data is stored in individual files. The files can have several formats. The DBMS came to replace the file systems. They have the following advantages over the DBMS. They are,

•       There is a centralized software which runs over the entire database and this helps managing the entire information easily.
•        This provides abstraction between the application programs and the way the data is stored and organized.
•        Integrity of data is established. You can verify that the integrity constraints are met easily. For example, assigning a new employee to meet a customer before accommodating a new customer.
•       Consistency of data is maintained as there are recovery methods to recover from any failure.
•       Concurrent access are permitted so that a user may feel that he is the only person accessing the data.
•       Redundancy of data is avoided.  
•       Flexibility is there as you can add new constraints to the database.
•      There is a problem of incompatible files when files are used.

               Internally the DBMS uses files to store the data in the hard disk. But it helps to programmer from caring about the way in which the data is stored and gives an environment to concentrate on the application development.

DBMS VS RDBMS :
              RDBMS is called the Relational Database Management. Here there exists relation between the tables. Relations can be one-to-one ,one-to-many ,many-to-many.
              RDBMS is a DBMS. But it adds more constraint in maintaining the relationships between tables.

What is a relationship in a RDBMS ?
       People usually come to know that RDBMS maintains relationships in database. So how is it maintained...?
         If there is a one-to-one or one-to-many relationship, it can be maintained by using a foreign key in the child table.
         In case of many to many relationships there needs an external relationship table to establish a relationship between the two tables.
         The relationship table will contain the primary keys of both table mapped against each other. This relationship table is used because to avoid redundancy of data in the child table.