Database Management System

Sub : DBMS  Batch : Bca IV Sem.

Definition of Database

Data are facts that can be recorded and have implicit meaning. Data refers to values such as names, telephone, addresses that can be easily stored inside diary, PC or floppy. Data is actually stored in the database and information refers to the meaning of that data as understood by user.

The database is collection of related data. A database has the following implicit properties.

i.          A database represents some aspect of the real world, sometimes called the miniworld or the Universe of Discourse (UoD). Changes to the miniworld are reflected in the database.

ii.         A database is a logically coherent collection of data with some inherent meaning.

iii.        A database is designed built and populated with data for a specific purpose. It has an intended group of users and some applications.

Database can be of any size. Example for Sources of databases are patients in hospital, bank, university, government department etc.

Definition of DBMS

DBMS means database Management System. It is a collection of programs that enables users to create and maintain database as well as enables to store, modify and extract information from the database. DBMS is software for defining, constructing and manipulating databases. It is also called database manager or database server.  Example of DBMS are Ms. Access, oracle, MYSQL, Ms. SQL server etc.

Thus the goal of DBMS is to provide an environment that is both convenient and efficient to use in retrieving and storing database information. In DBMS, user issue request for information then DBMS analyzes and some internal processing takes place and then the result is sent back to the user.

Definition of Database System

Database system is computerized record keeping system. e.g. Computerized library system, flight reservation system, automated teller machine etc. Database and the DBMS software collectively known as database system.

The following operations take place in the database system.

i.          Adding new / empty files to database.

ii.         Inserting, retrieving, updating, deleting data from existing database.

iii.        Removing existing files from database.

Fig. simplified picture of a database system

Fig. A simplified database system environment

Advantages of database system over paper based methods of record keeping are (i) compactness (ii) speed and (iii) accuracy

Characteristics of Database Approach

There are a no. of characteristics which distinguish the database from the traditional approach of programming with files. In the traditional approach of programming with files, many users may be using the same data such as student name separately. Thus data is duplicated and leads to wastage of storage space.

Main characteristics of database approach versus the file processing approach are as follows

i) Self describing nature of a database system

The definition or description of the database is stored in the system catalog separately and thus are available to users.

The system catalog stores structure and details of database only and no other data. thus the system catalog inside dbms describes database itself.

ii) Insulation between programs and data, and data abstraction

In traditional file processing, the changes the structure of data file may require changing all programs that access this file but the DBMS changes catalog information only. Thus both the program and data are independent and also called program data independence.

             Data abstraction : DBMS provides user with a conceptual representation of data that does not include many of details of how the data is stored or how the operations are being implemented. Suppose the example of car. People don't think of a car as set of tens of thousands of individual parts. They think of it as a well defined object with its own behavior. Similarly data abstraction hides the complexity. Data model is a type of data abstraction.

iii) Support of multiple views of data

A database typically has many users, each of whom may require a different perspective or view of the database. A view may be portion or subset of the database. It is also called virtual table as it may contain virtual data. Users shouldn't be given the whole privilege for security purpose about some users may not be aware of whether the data they refer to is stored or derived. The DBMS supports multiple news view of data in a multi-user DBMS.

iv) Sharing of data and multi-user transaction processing

Many user can select, update data at the same time. So dbms must support concurrency control. for example in applications such as train/bus reservation system, flight reservation system, many users use the system from different locations at the same time and so is sharing of data and multi-user transaction processing.

Advantages and benefits using DBMS

Advantages of using DBMS are as follows

i) Controlling redundancy

In traditional file processing system, each user maintains their own file and so there may be duplication of data. Storing same data multiple times lead to several problems such as wastage of space, duplication effort for entering data, data may become inconsistent.

ii) Restricting unauthorized access (security)

Confidential data should not be available to all users. User accounts with certain restrictions to data may be created for security. Similarly multiple views can be created for database security. In traditional file processing, if own get file gets everything & all data.

iii) Providing persistent storage for program objects and data structure

The values of program variables are discarded once the program terminates as in C, C++ pascal program unless the programmer write them in files. A complex object in C++ can be stored permanently in an object oriented DBMS.

iv) Permitting inferencing and actions using rules

Database system may be deductive or active. Deductive databases have capabilities for defining deduction rules for inferencing new information from stored database. It works like reporting system.

v) Providing multiple user interfaces

DBMS provides variety of interfaces for varying users. DBMS provide query language for casual user, programming languages for application programmers, forms and command for parametric users, menu driven interfaces for stand alone users. Form styles and menu driven interfaces are collectively called GUI (Graphical user interface)

vi) Representing complex relationship among data

Relationships may be created among data using DBMS which helps in managing the data and defining constraints for updating and deleting.

vii) Enforcing integrity constraints

Something that limits data is called constraints in database. For example, the minimum balance should not fall in a bank. It is a constraint. Some of the constraints are primary key, NOT NULL, check.

viii) Providing backup and recovery

DBMS provides facilities for taking backup of the database which can be used for recovery in case of failure of computer system or hardware system.

ix) Easy in accessing data

It becomes very easy and fast while accessing data from database using DBMS. Reports can be used for easy access of data.

x) Concurrent access to database

Many users can share the data at the same time and thus dbms provides users to access the database concurrently.