File system-and-database-chapter01-connoly

Introduction to Databases
Transparencies

© Pearson Education Limited 1995, 2005

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).


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.


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


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.


File-Based Processing


Limitations of File-Based Approach
Separation and isolation of data
– 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
– Same data is held by different programs.
– Wasted space and potentially different values
and/or different formats for the same item.


Limitations of File-Based Approach

Data dependence
– File structure is defined in the program code.

Incompatible file formats
– Programs are written in different languages, and so
cannot easily access each other’s files.

Fixed Queries/Proliferation of application
programs
– Programs are written to satisfy particular
functions.
– Any new requirement needs1995,new program.
© Pearson Education Limited a 2005

Database Approach
Arose because:
– 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).


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.


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.


Database Management System (DBMS)


Database Approach

Data definition language (DDL).
– 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.


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.


Views

Allows each user to have his or her own view of
the database.

A view is essentially some subset of the
database.


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


Components of DBMS Environment


Hardware
– Can range from a PC to a network of
computers.
Software
– 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.



Procedures
– Instructions and rules that should be applied to
the design and use of the database and DBMS.
People


History of Database Systems

First-generation
– Hierarchical and Network

Second generation
– Relational

Third generation
– Object-Relational
– Object-Oriented


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


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


Exercise : (lab session 9/8/07)
Discuss the roles of following personnel in database
environment: (people)

Data Administrator (DA)
Database Administrator (DBA)
Database Designers (Logical and Physical)
Application Programmers
End Users (naive and sophisticated)


File system-and-database-chapter01-connoly

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