Transcript Part 1 Introduction

Chapter 1,2
Introduction to Databases
Transparencies
CS424 Introduction of Database System
Chapter 1 - Objectives
Some common uses of database systems.
 Characteristics of file-based systems.
 Problems with file-based approach.
 Meaning of the term database.
 Meaning of the term Database
Management System (DBMS).

CS424 Introduction of Database System
Chapter 1 - Objectives
Typical functions of a DBMS.
 Major components of the DBMS
environment.
 Personnel involved in the DBMS
environment.
 History of the development of DBMSs.
 Advantages
and disadvantages of
DBMSs.

CS424 Introduction of Database System
Examples of Database
Applications
Purchases from the supermarket
 Purchases using your credit card
 Booking a holiday at the travel agents
 Using the local library
 Taking out insurance
 Renting a video
 Using the Internet
 Studying at university

CS424 Introduction of Database System
File-Based Systems

Collection of application programs that
perform services for the end users (e.g.
reports).

Each program defines and manages its
own data.
CS424 Introduction of Database System
Files Base Process
CS424 Introduction of Database System
File-Based Processing
1. Reading data from computer which scan the X-Ray
2. Weather data to be analyzed
3. The software which can read certain data and give
you the output
CS424 Introduction of Database System
Limitations of File-Based
Approach

Separation and isolation of data
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Each program maintains its own set of data.
Users of one program may be unaware of
potentially useful data held by other programs.
Duplication of data

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Same data is held by different programs.
Wasted space and potentially different values
and/or different formats for the same item.
CS424 Introduction of Database System
Limitations of File-Based
Approach

Data dependence
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Incompatible file formats
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File structure is defined in the program code.
Programs are written in different languages, and so
cannot easily access each other’s files.
Fixed Queries/Proliferation of
application programs

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Programs are written to satisfy particular functions.
Any new requirement needs a new program.
CS424 Introduction of Database System
Database Approach

Arose because:
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Definition of data was embedded in application
programs, rather than being stored separately and
independently.
No control over access and manipulation of data
beyond that imposed by application programs.
Result:

the database and Database Management System
(DBMS).
CS424 Introduction of Database System
Database
Shared collection of logically related data
(and a description of this data), designed
to meet the information needs of an
organization.
 System catalog (metadata) provides
description of data to enable program–
data independence.
 Logically related data comprises entities,
attributes, and relationships of an
organization’s information.
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CS424 Introduction of Database System
Database Management System
(DBMS)

A software system that enables users to
define, create, maintain, and control
access to the database.

(Database) application program: a
computer program that interacts with
database by issuing an appropriate
request (SQL statement) to the DBMS.
CS424 Introduction of Database System
Database Management System
(DBMS)
CS424 Introduction of Database System
Database Approach

Data definition language (DDL).
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Permits specification of data types, structures and
any data constraints.
All specifications are stored in the database.
Data manipulation language (DML).

General enquiry facility (query language) of the
data.
CS424 Introduction of Database System
Database Approach
 Controlled
access to database may
include:
a security system
 an integrity system
 a concurrency control system
 a recovery control system
 a user-accessible catalog.

CS424 Introduction of Database System
Views

Allows each user to have his or her own
view of the database.

A view is essentially some subset of the
database.
CS424 Introduction of Database System
Views - Benefits
Reduce complexity
 Provide a level of security
 Provide a mechanism to customize the
appearance of the database
 Present a consistent, unchanging picture
of the structure of the database, even if
the underlying database is changed

CS424 Introduction of Database System
Components of DBMS
Environment
CS424 Introduction of Database System
Components of DBMS
Environment
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Hardware
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Software
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Can range from a PC to a network of
computers.
DBMS, operating system, network software (if
necessary) and also the application programs.
Data

Used by the organization and a description
of this data called the schema.
CS424 Introduction of Database System
Components of DBMS
Environment
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Procedures
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Instructions and rules that should be applied to
the design and use of the database and DBMS.
People
CS424 Introduction of Database System
Components of Database
Management System (DBMS)
CS424 Introduction of Database System
DBMS Architecture
CS424 Introduction of Database System
DBMS Architecture

The Internal or Physical Level:
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The collection of files permanently stored on
secondary storage devices.
And it provides a low-level description of the physical
database, and an interface between the operating
system's file system and the record structures used in
higher levels of abstraction.
At this level record types and methods of storage are
defined, as well as how stored fields are represented.
CS424 Introduction of Database System
DBMS Architecture
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The Conceptual Level:
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It presents a logical view of the entire database,
which allows you to bring all the data in the database
together and see it in a consistent manner.
The first stage in the design of a database is to define
the conceptual view, and a DBMS provides a data
definition language DDL for this purpose.
The data definition language used to create the
conceptual level must not specify any physical
storage considerations that should be handled by the
physical level. It should not provide any storage or
access details, but should define the information
content only.
CS424 Introduction of Database System
DBMS Architecture

The External or View Level:
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It provides a window on the conceptual view which
allows the user to see only the data of interest to
them.
The user can be either an application program or an
end user. Any number of external views can be
defined and they can overlap each other.
The System Administrator and the DBA are special
cases. Because they have responsibilities for the
design and maintenance for the design and
maintenance of the database, they at times need to
be able to see the entire database. The external and
the conceptual view are functionally equivalent for
these two users.
CS424 Introduction of Database System
Roles in the Database
Environment
 Data Administrator
(DA)
 Database Administrator (DBA)
 Database Designers (Logical and
Physical)
 Application Programmers
 End Users (naive and sophisticated)
CS424 Introduction of Database System
History of Database Systems
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First-generation
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Second generation
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Hierarchical and Network
Relational
Third generation
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Object-Relational
Object-Oriented
CS424 Introduction of Database System
DBs Hierarchical 1960s
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The hierarchical data model organizes
data in a tree structure.
There is a hierarchy of parent and child
data segments.
This structure implies that a record can
have repeating information, generally in
the child data segments.
Data in a series of records, which have
a set of field values attached to it. It
collects all the instances of a specific
record together as a record type.
These record types are the equivalent
of tables in the relational model, and
with the individual records being the
equivalent of rows.
To create links between these record
types, the hierarchical model uses
Parent Child Relationships. These are a
1:N mapping between record types.
This is done by using trees,
CS424 Introduction of Database System
DBs Network 1970s
•data were more naturally modeled
with more than one parent per
child.
•So, the network model permitted
the modeling of many-to-many
relationships in data
•The basic data modeling construct
in the network model is the set
construct.
•A set consists of an owner record
type, a set name, and a member
record type. A member record type
can have that role in more than one
set
CS424 Introduction of Database System
Advantages of DBMSs
Control of data redundancy
 Data consistency
 More information from the same amount
of data
 Sharing of data
 Improved data integrity
 Improved security
 Enforcement of standards
 Economy of scale

CS424 Introduction of Database System
Advantages of DBMSs
Balance conflicting requirements
 Improved data accessibility and
responsiveness
 Increased productivity
 Improved maintenance through data
independence
 Increased concurrency
 Improved backup and recovery services
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CS424 Introduction of Database System
Disadvantages of DBMSs
Complexity
 Size
 Cost of DBMS
 Additional hardware costs
 Cost of conversion
 Performance
 Higher impact of a failure
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CS424 Introduction of Database System