chapter1 - dbms

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INTRODUCTION TODBMS


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Objectives

After completing this chapter, you will be able to:

Describe a database

Describe the goals of Database Management System

List the benefits of database approach

Describe various functions of a DBMS

List various data models

Describe Database Architecture

List the Role of DBA

List Various Database Models


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Basic Definitions

Data: Known facts that can be recorded and that haveimplicit meaning

Database:Collection of related data

Ex. names, telephone numbers and addresses of all

the people you know

Database Management System: A computerizedrecord-keeping system

A DBMS provides for storage, retrieval and updation of data in an

organized manner.


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Goals of a DBMS

To provide an efficient, as well as convenient

environment for accessing data in a database.

Enforce information security: database security,

concurrence control and crash recovery.

It is a general purpose facility for:

Defining a database

Constructing a database

Manipulating a database


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Benefits of Database Approach

Redundancy can be reduced

Inconsistency can be avoided

Data can be shared

Standards can be enforced

Security restrictions can be applied

Integrity can be maintained

The entity integrity rule states that the value

of the primary key can never be a null value


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DBMS Functions

Data Definition

Data Manipulation

Data Security and Integrity

Data Recovery and Concurrency

Data Dictionary

Performance

A DBMS is a complex piece of software

that usually consists of a number of

modules. It may be considered as an agent


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Database System

Stored Data

Defn.Stored Database

Software to access stored data

Software to process queries/programs

DBMS

Software

Application Programs/Queries

Users

DATABASE

SYSTEM


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Users

There are three broad classes of users:

Application programmers - Responsible for writing

application programs that use the database.End users - Interact with the system from workstations or

terminals.

Database Administrator (DBA) - Creates the actualdatabase.


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Facilities

A DBMS provides facilities for:

Describing the database, when a database is

being set up

Authorization specification and checking

Access path selection

Concurrency control

Logging and recovery

The main com onents of the DBMS are:


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user

query Q1

Database

schemeApplicationprogram query

Q2

Queryprocessor

DDL compiler

Database manager

File manager

Physicaldatabase

Compiledquery Q2 Database

description

Facilities continued...


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Internal level

(storage view)

Conceptual level(community user view)

External level(individual user

views)

Database

DBMS Architecture


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The three important characteristics of the database approach are:Insulation of programs and data (program-data and program-operation independence).

(b) Support of multiple user views.(c) Use of a catalog to store database description.

The three-schema architecture was proposed to achieve thesecharacteristics.

The internal level is the one closest to the physical

storage, i.e., it is the one concerned with the way

data is physically stored.

The external level is the one closest to the user, i.e.,

it is the one concerned with the way data is viewed by

Architecture continued...


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SNo FName LName Age Salary

SNo FNameLName Age Salary

SNo LName BranchNo

struct STAFF {

int staffNo;

int branchNo;

char fName[15];char lName[15];

struct date dateOfBirth;

float salary;

struct STAFF *next;

/* pointer to next Staff

record */};

index staffNo; indexbranchNo;

/* define indexes for staff */

BranchNo

Conceptual View

External View1

External View2

Internal

View

An Example of the Three Levels


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Change the schema at one level of a database system

without a need to change the schema at the next higher

level.

Logical data independence: Refers to the immunity of

the external schemas to changes in the conceptual schema

enables us to change the conceptual view without affecting

the external views.

Example: add new record or field

Physical data independence: Refers to the immunity of

the conceptual schema to changes in the internal schema.

Data Independence


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A set of concepts describing the structure of adatabase.

By structure, we mean the data types, relationships,

and constraints that should holds for the data.

Categories of Data Models

Conceptual Physical Representational

Data Model


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Types of Data Models

TABLEROW

COLUMN

VALUE

Hierarchical

Relational

Network


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Database Design Phases

DATA ANALYSIS

Entities - Attributes - Relationships - Integrity Rules

LOGICAL DESIGNTables - Columns - Primary Keys - Foreign Keys

PHYSICAL DESIGN

DDL for Tablespaces, Tables, Indexes


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Role of DBA

Defining the conceptual schema - conceptualdatabase design

Defining the internal schema - physical database

design and define the associated mapping between

the internal and conceptual schemas

Liaison with users

Defining security and integrity rules

Defining backup and recovery procedures

Monitoring performance and responding to changing

requirement


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Various Databases Models

Relational Model Network Model

Hierarchical Model

Relational model: In this model, eachdatabase item is viewed as a record with

attributes. A set of records with similarattributes is called a table. Most of thepopular commercial DBMS products likeOracle, Sybase, MySQL, etc. are basedon relational model.

Network model: This model represents


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Summary

You should now be able to:Describe a database

Describe the goals of Database Management System

List the benefits of database approach

Describe various functions of a DBMS

List various data models

Describe Database Architecture

List the Role of DBA

List Various Database Models

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