Final Mis Done

8/3/2019 Final Mis Done

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INTRODUCTION

What Is a DBMS?

A Database is a collection of recordsand data in structured format so that datacan be easily retrieved for analysis andcalculations.


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What Is a DBMS?

A Database Management System is a system that

creates, manages, and controls a database used

by managers for analysis and decision making.


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Why Study Databases??

To understand :-

The importance of storing data. The roles of data models.

Views of business users and database designers.

The concept of sharing data.

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Why Use a DBMS?

Data independence and efficient access.

Reduced application development time.

Data integrity and security.

Uniform data administration.

Concurrent access, recovery from crashes.


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Applications of DBMS

SalesReporting

OrderProcessing

Payroll

PerformanceAppraisal

Marketingapplication

Financeapplication

HRISapplication

DatabaseMgmtSystemIntegrateddata store

Marketingapplication


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Database management system

A database management system is a system which defines, interprets,manipulates and maintains a collection of databases which are entirelyseparate in structure. DBMS is the major component of database system.

There are many different types of DBMSs, ranging fromsmall systemsthat run on personal computers to huge systems that runon mainframes.

The following are examples ofdatabase applications:

Banking System and ATM's machines.

Credit Card/Credit Limit Check System.

computerized library systems

flight reservation systems

computerized parts inventory systems

Different DBMSs support different query languages, although there is asemi-standardized

query language called SQL(structured query language).Sophisticated languages for managing database systems are called fourth-generation languages, or 4GLsfor short.
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The information from adatabase can be presentedin a variety of formats:

Most DBMSs include a reportwriter programthat enablesyou to output data in theform of a report.

Many DBMSs also includea graphics component thatenables you to outputinformation in the form ofgraphs and charts.

Formats

Report

writer

Graphics


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Diagram of DBMS


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Components of DBMS

components

data

Hard-ware

Soft-ware

user


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Advantages of a DBMS

Provides the way for storage

Centralized control and an easy access

Provides the way for doing simple and complexqueries

Arranging data in various ways

Maintain non redundancy of data

Maintain security and privacy of data

Access to multi users


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Disadvantages of DBMS

Costly due to requirements of expensivehardware

Higher operating costs

Greater complexity of backup and recoveryin multiuser environment

High risk of data loss due to centralized ofdatabase


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STRUCTURE OF A DBMS

DATA DEFINITION LANGUAGE (DDL)

DATA MANAGER

FILE MANAGER

DISK MANAGER

QUERY MANAGER

DATA DICTIONARY


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ROLE OF DBMS IN BUILDINGSYSTEMS

DBMS are very popular packages formicrocomputers

Examples of leading DBMS

It provides user friendly interface

Easy to manage application


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Data Models

A data model is a collection of concepts fordescribing data.

A schemais a description of a particularcollection of data, using the given data model.

The relational model of datais the most widelyused model today.

Main concept: relation, basically a table with rows

and columns.

Every relation has a schema, which describes the

columns, or fields.


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Types of data models and schema

Conceptual schema:1. This schema is concerned with the overall logical

model of the database.

2. It is mainly concerned with representation of

information in the abstract from as compared to theway in which data is actually stored.

3. Example:-

in a payroll system , the information about

employee no.(4 characters), employeename(20) andbasic salary (8 digits) is the conceptual view of thedatabase.


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External schema:-

1. It is concerned with the user-orientedway of viewing the data.

2. This schema is also termed as sub-schema.

3. Example:-

in a payroll system , the employee nameand his basic salary as viewed by theuser is the external view of the database.


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Contt..

Internal schema:-

1. It is concerned with the actual storagedesign of data.

2.

It reflects how the data is stored in andaccessed from the physical storage.

3. Example:-

in a payroll system , the information about

how the employee no., employee name andbasic salary are stored is the internal viewof the database.


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1. To Modify the Structure of the Table:

In order to add new fields or deleteexisting fields we have to modify thestructure of the table. To do this,

Select the table name.

Right-click on the selected name for theshort-cut menu.

Click on design. The table structure window is displayed

where changes can be made


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Structured Query Language

SQL developed by IBM , is a standard datadefinition and data manipulation languageof relational databases.

It is designed to define , access , querry ,organise and update the data andinformation in relational databases.


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Contt

To create a table of supplier database inSQL :

CREATE TABLE SUPPLIER

(SUPPNO CHAR (3) NOT NULL.SUPPNAME CHAR(20),

CITYCODE NUMBER(2),

CITYNAME CHAR(3));

To query the database , the followingstatement is used:


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Contd...

SELECT SUPPNO, SUPPNAME, CITYCODE ,CITYNAME

FROM SUPPLIER

WHERE SUPPNO = S01;


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2. To modify/delete the data in the table:

In order to edit data, or delete existingrecords or add new records to the table,


Right-click on the selected name for theshort-cut menu

Click on Open. The data window is displayed where data

can be edited, deleted or added.


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3. To Rename a table:

In order to change the name of a table,


Right-click on the selected name for theshort-cut menu.

Click on Rename.


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4. To Delete a table:

In order to delete a table from thedatabase,

Select the table name. Right-click on the selected name for the

short-cut menu.

Click on delete.


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5. To Return to VB:

Select File > Exit to exit from Visual Data

Manager and return to VB.


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Database locking

Database locking is a mechanism by which two userswill be prevented from updating the same record at thesame time. The Microsoft Jet database engine provides3 levels of locking.

1. Database locking: Only one user can access thedatabase.

2. Table locking: Only one user can access the table.

3. Page locking: The Microsoft jet database engineautomatically performs page locking which is to lock

one page of data (normally about 2KB) in which therecord is present.


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What is Normalisation ?

Normalization is the basis of designingrelational databases

Process of simplifying the data structureby replacing it with smaller and multipledata structure

Study of relations between tables andattributes


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Goals of normalisation

Minimizing the redundant data

Reducing inconsistent data

Designing data structures for easiermaintainance


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Types of normal forms

First normal form

Second normal form

Third normal form


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First normal form (1NF)

No duplicated rows in the table Each cell is single valued

Entries in the column is of same kind

Second normal form (2NF) All non key attributes are dependent on key

All column depends on the primary key only

Each record in a table should be uniquelyidentifieable trough a single column


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Contt

Third normal form

A relation is said to be in third normalform if no non keyfield depends on

another non-key field


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Denormalisation:-

Denormalisation is a processs ofattempting to optimize the readperformance of a database by addingredundant data or by grouping data


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Basic DBMS types

Hierarchical structure

Trees of records: one-to-many relationships

Limitations: Requires duplicating records (e.g. many-to-many

relationship)

Problems when updated

Retrieval requires knowing the structure (limited data

independence): traversing the tree from top to bottom using a procedural

language


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Contt.

Network structure: similar to the hierarchical database with theimplementation

of many-to-many relationships

Relational structure

Object-Oriented structure

Objects (collection of data items and procedures) andinteractions between them.

Is this really a new paradigm, or a special case of networkstructure?

Separate implementation vs. implementation on top of aRDBMS


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Relational structure

Relations, attributes, tuples

Primary key (unique combination of attributes for each tuple)

Foreign keys: relationships between tuples (many-to-many).

Example: SUPPLIES defines relations between ITEM andSUPPLIER

tuples.

Advantages: many-to-many relationships, ,high level declarative query language (e.g. SQL)

h d l


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The Transaction Model

Examples of primitives for transactions.

Primitive Description

BEGIN_TRANSACTION Make the start of a transaction

END_TRANSACTION Terminate the transaction and try to commit

ABORT_TRANSACTION Kill the transaction and restore the old values

READ Read data from a file, a table, or otherwise

WRITE Write data to a file, a table, or otherwise


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Conclusion:-

As we have seen DBMS is a collection ofrecords and data in structured format sothat data can be easily retrieved for

analysis and calculations. Hence DBMS is very important for any

organization.


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Reference:-

DBMS book of Bsc(I.T) by Himalayaprakashan.

Introduction to Computers By A. Leon & M

Leon.


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