Few Basic DBMS Concepts : Shambhu Kr Jha

Introduction

Almost everyone uses a database in one form or another. The e-mail client stores address data and archived e-mail messages. Big business houses use databases to store customer information, product details, details of their competitors and various other details related to their business.  The IRS maintains a database with tax records for every person who files a tax return. With increase in volume of data to manage and complexity in business process there is huge demand of a software system which can help in meeting the individual needs.  Database management software helps people maintain data on every level, from the smallest personal database, to the largest commercial database.  

DBMS (database management system) tools are used to analyze and manipulate databases. Most commercial DBMSs use the relational model, the relational database management system (RDBMS) is perhaps the most popular type of DBMS in use today. It is an industry-standard

A database is a collection of relevant data. A database management system (DBMS) is a set of computer-based application programs that support the processes of storing, manipulating, retrieving and presenting the data within the database. The data within the database are organized into tables, records, and fields.

A table holds a set of data that are logically related. For example, the data used to describe and distinguish the various customers of a company would be stored within a "Customer" table. The data used to describe the products of the company would be stored within a "Products" table.

 

Some Important Characteristics of  DBMS

ð         1. DATA INDEPENDENCE

Users of the DBMS are insulated from the physical details of data storage.

ð         2. DATA ABSTRACTION

Users sEe only a conceptual view of the database.   Implementation details are hidden.

ð         3. Multiple Users Support

Views – SUBSETS OF THE DATABASE OR VIRTUAL DATA

ð   4. Concurrency CONTROL Mechanism.

              

ð    5.    database integrity

            6. DBMS USER TYPES (GENERALIZED)

ð         End Users               

Access

Manipulation

ð         DATABASE DESIGNERS/PROGRAMMERS

Definition  

Construction

Access

Manipulation

ð         Database Administrator

Security

Performance

Coordination

Access Control

Characteristics of DBMS

Ø  Data Redundancy

Data redundancy is a data organization issue that allows the unnecessary duplication of data within your database. A change or modification, to redundant data, requires that you make changes to multiple fields of a database. The data relationships, inherent in a relational database, should allow you to maintain a single data field, at one location, and make the database’s relational model responsible to port any changes, to that data field, across the database. Redundant data wastes valuable space and creates troubling database maintenance problems.

To eliminate redundant data from your database, you must take special care to organize the data in your data tables. Normalization is a method of organizing your data to prevent redundancy. Normalization involves establishing and maintaining the integrity of your data tables as well as eliminating inconsistent data dependencies.

Establishing and maintaining integrity requires that you follow the prescribed rules to maintain parent-child, table relationships. Eliminating inconsistent, data dependencies involve ensuring that data is housed in the appropriate database table. An appropriate table is a table in which the data has some relation to or dependence on the table.

Ø  Data Integrity:

It is important that data stick on to a predefined set of rules, as determined by the database administrator or database designer. The integrity of the data in a relational database must be maintained as multiple users access and change the data. Whenever data is shared, there is a need to ensure the accuracy of the values within database tables

Types of Data Integrity:

This section describes the rules that can be applied to table columns to enforce different types of data integrity.

 

1.Null Rule

A null rule is a rule defined on a single column that allows or disallows inserts or updates of rows containing a null (the absence of a value) in that column.

 

2.Unique Column Values

A unique value rule defined on a column (or set of columns) allows the insert or update of a row only if it contains a unique value in that column (or set of columns).

 

3. Primary Key Values

A primary key value rule defined on a key (a column or set of columns) specifies that each row in the table can be uniquely identified by the values in the key.

 

4. Referential Integrity Rules:

A referential integrity rule is a rule defined on a key (a column or set of columns) in one table that guarantees that the values in that key match the values in a key in a related table (the referenced value).

Ø    Multiuser Support: A database system can be used by large number of users for large number of application program. This feature of DBMS reduces the delicacy of data  in the database. We can create different view of data according to the requirement of the user and allow them to access it. Even same data can be used for n number of application program in different manner. A database system has even different category of user who will be using the data in a different manner. So this feature of DBMS has made it very popular.