RDBMS (Relational Database Management Systems) .A database management system (DBMS) consists of a

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Transcript of RDBMS (Relational Database Management Systems) .A database management system (DBMS) consists of a

1

RDBMS

(Relational Database

Management Systems)

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Introduction to DBMS

Data and Information

Where data is some meaningful fact or

figure, information is the processed data

on which decisions and actions are based.

Information can also be defined as the

organized and classified data to provide

the meaningful values to the receiver.

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Data

Input

or

Information

output

orProcess

Data processing: It is the step-by-step refinement of data

to get out the desired information.

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Database Management System Definition

A database management system (DBMS) consists of acollection of interrelated data and a set of programs to accessthat data. The collection of data, usually referred to as thedatabase, contains information about one particular enterprise.

The primary goal of a DBMS is to provide an environment thatis both convenient and efficient to use in retrieving and storingdatabase information.

Database systems are designed to manage large bodies ofinformation. The management of data involves both thedefinition of structures for the storage of information and theprovision of mechanisms for the manipulation of information.

In addition, the database system must provide for the safety ofthe information stored, despite system crashes or attempts atunauthorized access. If data is to be shared among several users,the system must avoid possible inconsistent results.

5

Contd

The importance of information in most organizations, andthe value of the database, has led to the development of alarge body of concepts and techniques for the efficientmanagement of data.

A database management system is also a collection ofsoftware programs that stores data, organizes the data intorecords, and allows access to the data in a uniform andconsistent way.

In a database management system (DBMS), applicationprograms do not obtain the data they need directly from thestorage media. They must first request the data from theDBMS. The DBMS then retrieves the data from the storagemedia and provides them to the application programs.

Thus a database management system operates betweenapplication programs and the data.

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Relationship of application programs, a database management system, and a

database.

Application

program

Application

program

Application

program

Database

Management

System

Database

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Purpose of Database Systems.

The purpose of the database systems is

replace the conventional file processing

system which has major disadvantages, to a

robust system, which is capable of storing

the data by eliminating redundancy,

inconsistency, security problems and

integrity problems.

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The typical file-processing system has a

number of disadvantages:

Data redundancy and inconsistency.

Difficulty in accessing data.

Data Isolation.

Concurrent access anomalies.

Security Problems.

Integrity problems.

Data Abstraction. Data abstraction is the reduction of a particular body

of data to a simplified representation of the whole.

Abstraction, in general, is the process of taking away

or removing characteristics from something in order

to reduce it to a set of essential characteristics. As in

abstract art, the representation is likely to be one

potential abstraction of a number of possibilities.

A database abstraction layer, for example, is one of a

number of such possibilities.

9

Contd..

Data abstraction is usually the first step in database

design. A complete database is much too complex a

system to be developed without first creating a

simplified framework. Data abstraction makes it

possible for the developer to start from essential

elements -- data abstractions -- and incrementally add

data detail to create the final system.

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Data Abstraction(contd.. ) A database management system is a collection of

interrelated files and a set of programs that allow users toaccess and modify these files.

A major purpose of a database system is to provide userswith an abstract view of the data. That is, the systemhides certain details of how the data is stored andmaintained.

However, in order for the system to be usable, data mustbe retrieved efficiently. This concern has lead to thedesign of complex data structures for the representationof data in the database.

Since many database systems users are not computertrained, the complexity is hidden from them throughseveral levels of abstraction in order to simplify theirinteraction with the system.

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Three levels of abstraction.

View

level 1

Physical level

Conceptual

Level

View

level 2

View

level n

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Physical level: The lowest level of abstraction describes what areactually stored. At the physical level, complex low-level datastructures are described in detail.

Conceptual level: The next higher level of abstraction describeswhat data are actually stored in the database, and the relationshipsthat exist among the data. Here the entire database is described interms of a small number of relatively simple structures. Althoughimplementation of simple structures at the conceptual level mayinvolve complex physical-level structures, the user of theconceptual level need not be aware of this. The conceptual levelof abstraction is used by database administrators, who must decidewhat information is to be kept in the database.

View Level: The highest level of abstraction describes only partof the entire database. Despite the use of simpler structures at theconceptual level, some complexity remains because, of the largesize of the database. Many users of the database system will notbe concerned with all of this information. Instead, such users needonly a part of the database. To simplify their interaction with thesystem, the view level of abstraction is defined. The system mayprovide many views for the same database.

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Overall System Structure.

Nave Users Application Programmers Sophisticated Users Database administrator

(daily data users)Application

interfaces

Application

programs

Query Database

scheme

Application

programs

object code

DML Pre

CompilerQuery

Processor

Database

manager

DDL

compiler

Disk Storage

File

manager

Data files

Data

dictionary

Database

Management

System

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Overall System Structure.

A database system is partitioned into modules that deal with each of the responsibilities of the overall system.

In most cases, the computers operating system provides only the most basic services and the database system must build on that base.

Thus, the design of a database system must include consideration of the interface between the database system and the operating system.

The function components of a database system include:

File manager

Database manager

Query processor

DML pre-compiler

DDL compiler

In addition, several data structures are required as part of the physicalsystem implementation, including:

Data files

Data dictionary

Indices

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What is a database?

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Anatomy of a Database

Data

Definition

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Anatomy of a Database

3GL

Manipulation

Indices

Data

Definition

Data

Manipulation

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Anatomy of a Database

Etc.

Security

Maintenance

GUI

3GL

Manipulation

4GL Query

Processor

Indices

Data

Data

Definition

Data

Manipulation

Data

Control

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Try to think why each of these need to use a database:

Supermarkets

Insurance

Credit Cards/Banking

Libraries

Travel Agents

Universities

Engineering

Common Uses of Databases

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DEFINITION

A collection of application programs that perform

services to end users.

Each program defines and manages its own data.

File Based Systems

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Data Entry

& Reports

File handling

Routines

File Definition

Sales Files

Data Entry

& Reports

File handling

Routines

File Definition

Lease Files

File Based Processing

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Separation & Isolation of Data

Data Dependence

Duplication of Data

Incompatible file formats

How do we resolve these problems?

Limitations of File Based

Systems

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DEFINITION

A shared collection of logically related data

designed to meet the information

requirements of an organisation

The Database Approach

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Data Entry

& reports

Data Entry

& reports

DBMS

Leases App. Programs

Database

Database Processing

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DEFINITION