Database Management System

It is a collection of programs that enables user to create and maintain a database. In other words it is general-purpose software that provides the users with the processes of defining, constructing and manipulating the database for various applications.

Database management systems frees the programmer from the need to worry about the organization and location of data. The primary goal of a DBMS is to provide an environment which is both convenient and efficient to use in retrieving and storing information.

DATABASE STORAGE HIERARCHY

1) DATABASE

A collection of data files integrated and organised into a simple comprehensive file system, which is arranged to minimize duplication of data and to provide convenient access to information within that system to satisfy a wide variety of user needs.

2) DATA FILES

Datafile is the file which actually physically keeps the data in secondary storage device. It represents the physical representation of the database.

3) DATA OBJECTS(Tables)

Objects such as tables, procedures, functions, etc, especially TABLES logically keep the data stored together. These objects may me spread across one or more physical data files. Tables or Relations are Entity Sets.

4) RECORDS

A collection of related items of data that are treated as a unit. It is the information about an entity.

eg:- An employee record would be collection of all fields of one employee.
Record is sometimes referred as tuple.

5) FIELD

Individual element of data is called Field.
eg:- Bank cheque consist of following field cheque no, date, payee, numeric amt, signature, bank,etc.

Field is sometimes referred as Data item Or column or attribute.

Introducing Relational Databases

Relational Model Paradigm

1)         In a DBMS, relation between two files is created and maintained programmatically. Hence the relation is temporary.

In a RDBMS, relation between the two tables can be created at the time of table creation or later on, and hence it is permanent

2)         In a DBMS, we have the concept of Fields, Records and Database Files

In a RDBMS, we have the concept of Column(attribute), Row(Tuple or Entity) and Table(Relation or Entity Class/Set or Applet)

3)         IN a DBMS, Network traffic is high, since most of the processing is done at the client or requestors side.

In a RDBMS, network traffic is low, since most of the processing is done at the Server side

4)         DBMS does not support the Client-Server architecture. It is a point-to-point communication between two machines

            Most of the RDBMSs support the Client-Server Architecture

Example MS Access is a RDBMS, which does not support the Client-Server Architecture.

5)         In a DBMS, we have file –level locking.

            In a RDBMS, we have table, as well as Row-level locking

6)         In a DBMS, there is no support for Distributed-Database Concept

            In a RDBMS, there is support for a Distributed-Database Concept

7)         In a DBMS. There is no Security of Data.

In a RDBMS, we have multiple levels of Data-Security like i)Logging in Security ii) Command Level Security iii)Object Level Security

8)         In a RDBMS, we have the concept of Data-Dictionary(or Meta-Data or Data about Data) implemented in the form of System Tables and Views.

                        In a DBMS, there is no Data-Dictionary concept.