Chp 1-Introduction to Database

8/4/2019 Chp 1-Introduction to Database

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Chapter 1

Introduction to Databases

Pearson Education 2009


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Chapter 1 - Objectives

u Some common uses of database systems.

u Characteristics of file-based systems.

u Problems with file-based approach.

u

ean ng o e erm a a ase.u Meaning of the term Database Management

System (DBMS).



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Chapter 1 - Objectives

u Typical functions of a DBMS.

u Major components of the DBMS environment.

u Personnel involved in the DBMS environment.

.

u Advantages and disadvantages of DBMSs.



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Examples of Database Applications

u Purchases from the supermarket

u Purchases using your credit card

u Booking a holiday at the travel agents

u

s ng e oca raryu Taking out insurance

u Renting a video

u Using the Internet

u Studying at university



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File-Based Systems

u Early attempt to computerise the manual filing

system and developed in response to the needsof industry for more efficient data access

u Collection of application programs thatperform services for the end users (e.g. reports)

u Each program defines and manages its own

data (decentralised approach)

Because of this, there are limits as to how that

data can be used or transported.Pearson Education 2009


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File-Based terminology

u File consist of a number ofrecords

Each record may correspond to some real

world object or concept e.g. Bank account, a

ran ac i n a r n

u These are logically related data

u Each record is a series offields

Each is an aspect or attribute of the objectdescribed



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File-Based Processing



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Limitations of File-Based Approach

u Separation and isolation of data

Each program maintains its own set of data.

Information needed for a particular task maybe in different files or even differentdepartments files

Users of one program may be unaware ofpotentially useful data held by other programs.

u Duplication of data Same data is held by different programs.

Wasted space and potentially different values

and/or different formats for the same item.Pearson Education 2009


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Limitations of File-Based Approach

u Data dependence

File structure is defined in the program code.

Application program handle physical storage ofdata as well as content

u Incompatible file formats Programs are written in different languages, and so

cannot easily access each others files.

u Fixed Queries/Proliferation of applicationprograms

Programs are written to satisfy particular functions.

Any new requirement needs a new program.Pearson Education 2009


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Database Approach

u Arose because:

Definition of data was embedded in applicationprograms, rather than being stored separately andindependently.

No control over access and mani ulation of data

beyond that imposed by application programs.

u Result:

the database and Database Management System(DBMS).



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Database

u Shared collection of logically related data (and

a description of this data), designed to meet theinformation needs of an organization.

u Database holds the operational data and alsodescription of this data.

u System catalog (data dictionary or metadata)provides description of data to enableprogramdata independence.



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Database

u Logically related data comprises;

entities (distinct object- a person, place,thing, etc),

Attributes (a property that describes some

aspect of the object that we wish to record), and relationships of an organizations

information.

u The database holds data that is logicallyrelated



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Database Management System (DBMS)

u A software system that enables users to define,

create, maintain, and control access to thedatabase.

u (Database) application program: a computer

program that interacts with database by

issuing an appropriate request (SQL

statement) to the DBMS.



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Database Management System (DBMS)



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Database Approach

u Data definition language (DDL).

Permits specification of data types, structures andany data constraints.

All specifications are stored in the database.

u Data manipulation language (DML).

General enquiry facility (query language) of the

data.



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Database Approach

u Controlled access to database may

include: a security system prevents unauthorized users accessing the

database

an integrity system maintains the consistency of stored data.

a concurrency control system allows shared access ofdatabase

a recovery control system restores the database to aprevious consistent state following a hardware or software failure

a user-accessible catalog contains descriptions of the datain the db.



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Views

u Allows each user to have his or her own view of

the database.

database.



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Views - Benefits

u Reduce complexity by letting users see the data the way they want it

u Provide a level of security can exclude data that some users shouldnot see

u Provide a mechanism to customize the appearance of the database

we can change the display using different name rentMonthly Rent

u resen a cons s en , unc ang ng p c ure o e s ruc ure o e

database, even if the underlying database is changed if wechanged the database, and these fields are not required by the view, the

view is not affected



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Components of DBMS Environment



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u Hardware

Can range from a PC to a network ofcomputers.

u Software

DBMS, operating system, network software (ifnecessary) and also the application programs.

u Data

Used by the organization and a descriptionof this data called the schema.



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u Procedures

Instructions and rules that should be applied tothe design and use of the database and DBMS.

Users who mana e the database re uire

documented procedures on how to use or runthe systems

u People

People involved with the system



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Roles in the Database Environment

u Data Administrator (DA) responsible for the management of

the data resource

u Database Administrator (DBA) responsible for the physicaldb design and implementation, security and integrity control,

u Database Designers (Logical and Physical) identifyingthe data (entities, attributes, relationships & constraints)

u Application Programmers - developer

u End Users (naive and sophisticated) - clients



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History of Database Systems

u First-generation

Hierarchical and Network

u Second eneration

Relational

u Third generation

Object-Relational Object-Oriented



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Advantages of DBMSs

u Control of data redundancy by integrating the files so that multiplecopies of the same data are not stored

u Data consistency reduce the risk of inconsistencies occurring (data isupdated only once)

u More information from the same amount of data can deriveadditional information from the same data

u

Sharing of data data shared by all authorized usersu Improved data integrity refers to the validity & consistency of stored

data

u Improved security protection from unauthorized user

u Enforcement of standards allows DBA to define the DBMS toenforce necessary standards (naming conventions, access rules etc.)

u Economy of scale- combining data save cost



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Advantages of DBMSs

u Balance conflicting requirements DBA make decisions on

operational use of databaseu Improved data accessibility and responsiveness DBMS

provides query language that allow user asks ad hoc information

u Improved maintenance through data independence

u Increased concurrency DBMS can manage concurrent dbaccess

u Improved backup and recovery services



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Disadvantages of DBMSs

u Complexity failure in designing can lead bad design decision

u Size occupying large disk space & memory to run efficiently

u Cost of DBMS depending on the functionality provided

u Additional hardware costs sometimes need to purchase additionalstorage space

u

Cost of conversion purchasing extra hardware and to train staffu Performance DBMS cater for many application may not run as fast as

they used.

u Higher impact of a failure all users & applications rely on theavailability of the DBMS , if failure of certain components can bring

operation to a halt.



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Discussion

u Why would you choose a database system

instead of simply storing data in operatingsystem files? When would it make sense not to

use a database system?



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Useful links

u http://www.oracle.com

u http://www.microsoft.com/sql and

http.microsoft.com/access

u http://www.ibm.com/db2

u http://www.mysql.com

u http://en.wikipedia.org/wiki/databaseu http://en.wikipedia.org/wiki/DBMS

u http://www.planetids.com/content/3rd-generation-database-

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