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Transcript of 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