chp 1-introduction to database
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Chapter 1
Introduction to Databases
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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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Components of DBMS Environment
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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Components of DBMS Environment
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-
technolohy-part-i
u http://www.planetids.com/content/3rd-generation-database-
technolohy-part-ii
u http://www.planetids.com/content/3rd-generation-database-
technolohy-part-iii Pearson Education 2009