earning Objective At the end of this module, students should be able to define and identif the followin s: •
Some common uses of database systems (db).
•
Characteristics, problems and differences between file-based approach and db approach.
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Meaning of terms - db, Database Meaning Database Management Management System (DBMS), db application system, db system
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Personnel involved in the DBMS environment.
•
Advantages and disadvantages of DBMSs
•
Three-Level ANSI-SPARC ANSI-SPARC Architecture
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Introduction •
The now an integral dayto to-da -dadatabase li life fe that thatisoft often en such we we ar are e no not t aw awar areepart we of aare reour u usi sin n one • We will examine some applications of database system • We will use so some me terminology in this chapter : – database
: a collection of related data (databasee management management system) : the software that – DBMS (databas manages & controls access to the database – database application : a program that interacts with the database at some point in its execution – database system : a collection of application programs that interact with the database along with the DBMS and database itself
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Overview of DB System DB SYSTEM
.... ....
.... ....
DBMS
DB
DB USER APPL ICATION ICATIONS S 4
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Traditional File Based System •
An early attempt to computerize the manual filing
•
Definition – Collection of application programs that perform services for the end users (e.g. reports). Each program defines and manages its own data. • Works well while the number of items to be stored is small. However, However, it breaks down when we have to cross-reference or process the information in the files.
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File Based Processing
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File Based Processing •
Figure shows each department accessing their own for them.
•
Each set of departmental application programs handles data entry, file maintenance, and the generation of a fixed set of specific reports. records are defined in the application code
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Limitations of File-Based Approach Approach •
Se ara aratio tion n and and isol isolati ation on of of data data – Each
program maintains its own set of data.
– Users
of one program may be unaware of potentially useful data held by other programs.
•
– Same
data is held by different programs.
– Wasted
space and a nd potentially different values and/or different formats for the same item. 8
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Limitations of File-Based Approach Limitations •
Data dependence – – Changes
•
.
to an existing structure are difficult to make
Incompatible file formats – Programs
are written in different languages, and so cannot easily access each other’s files.
programs – Programs – Any
are written to satisfy particular functions.
new requirement needs a new program. 9
Database Approach •
The limitations of the file-based approach can 1. Definition Definition of data data was embedd embedded ed in appli applicatio cation n programs, rather than being stored separately and independently. 2. No control control over access and manipul manipulation ation of data data beyond that imposed by application application programs.
•
Result, a new approach was required: –
the database and Database Management System (DBMS). 10
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The Database •
Definition : – Shared
collection of logically related data (and a description o s a a , es e s gne o mee e n orma on nee s o an organization.
•
A database is also defined as a self-describing collection of integrated records – The
description of the data is known as the system catalogue (metadata) to enable program–data enable program–data independence. independence. – The definition of data is separated from the application program. definiti on and – The users of an object only see the external definition unaware of how the object is defined and how it functioned •
Logically related data comprises entities, attributes and relationships of an organization’ organization’ss information.
,
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Database Management System (DBMS) •
DBMS is the software that interacts with the user’ user ’s
•
Definition - A software system that enables users to define, create, and maintain the database and that provides controlled access to this this database. 1. 2. 3.
•
Define using Data Definition Language (DDL) Create insert, update, delete & retrieve data using Data Mani ulation Lan ua e DML Contr tro olled ac accces esse sed d security, integrity, concurrency control, recovery & user-accessible catalog
Example of DBMS – Micro Example Microsoft soft Access Access,, Mic Microsoft rosoft SQL Server, Server, Oracle, Sybase and etc. 12
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Database Management System (DBMS) •
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.
– Using
Structured Query Language (SQL) to produce required information.-
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Database Application Programs •
– A
computer program that interacts with the database by issuing an appropriate request (typically (typically an SQL statement) to the DBMS
•
Users interact with the database through a number of application programs (used to create & information) written in some programming language 14
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Database Application Programs •
Figure shows each department using their through the DBMS. – Each
set of departmental application programs handles data entry, file maintenance, and the generation of a fixed set of specific reports. – The physical structure & storage of the data are now •
A view mechanism. – Provides users with only the data they want or need to use. 15
Database Application Programs Application Appli cation Prog Program ram
DATABASE SYSTEM
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Components of DBMS Environment
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Roles in the Database Environment Environment
– responsible
for the management of the data
resource •
Database Databa se pla planni nning ng • Development and maintenance of standards, po c es, proce ures • Con Concep ceptua tual/l l/logi ogical cal dat databa abase se desi design gn
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Roles in the Database Environment Environment • Database Administrator (DBA) – responsible
for the physical realization of the
database • Physical database design and implementation • • Maintenance of operational control • Ensuring satisfactory performance of applications for users 19
Roles in the Database Environment Environment • Database Designers (Logical and
Physical) – Logical
: is concerned with identifying the data, the relationships between the data, & the constraint on the data that is to be stored
– Physical
: decides how the logical database design is to be physically realized 20
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Environment Roles in the Database Environment •
pp ca on ro rogrammers – build
the application programs programs that provide the required functionality for the end-users
• End Users – naive
and sophisticated
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File-based Approach
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Adv antag es of Dat abase Ap pro ach : Control of data redundancy Data consistency More information from the same amount of data Sharing of data Improved data integrity integrity & s ecurity Improved data accessibility and responsiveness Increased Increa sed productivit y Improved maintenance through data independence Increased Increa sed conc urrency 22 Improved backup and recovery services
Limitation of File Based Approach : Separation and isolation of data Separation Duplication of data Data dependence Incompatible file formats Fixed Queries/Proliferation Queries/Proliferation of application programs
Database Approach
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Three-Level Architecture •
All DBMS are built based on the 3-Level Architecture
•
All users should be able to access same data.
•
A user’ r’ss view is immune to chan es made in other views.
•
Users should not need to know physical database storage details. 23
Three-Level Architecture •
DBA should be able to change database
s orage s ruc ures w ou a ec ng e users’ views. • Internal structure of database should be unaffected by changes to physical aspects . • DBA should be able to change conceptual structure of database without affecting all users. 24
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ANSI-SPARC ARC Three-Level Architecture ANSI-SP
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ANSI-SPARC ANSI-SP ARC Three-Level Architecture • External Level – Users’ views of the
database. – Describes that part of database that is relevant to a particular user user..
• Conceptual Level – Community
view of the database. – Describes what data is stored in database and relationships among the data. 26