Transcript Introduction to database system

Introduction to database system
What is a Database system?
Data System Components
Data
Hardware
Software
User
What is Database
Benefits of Database Approach
Database System
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Database system is a computerized
record-keeping system. It is a computerize
system whose overall purpose is to store
information and to allow users to retrieve
and update that information on demand.
– Information is anything that is significant
to the individual or organization
concerned.
Data VS Information
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Data is used to refer to what is
actually stored in the database
Information is used to refer to
meaning of that data as understood by
some user.
Operations
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Adding new file to database
Inserting data into existing files
Retrieving data from existing files
Deleting data from existing files
Changing data in existing files
Removing existing files from the
database
Database System
Components
Data
 Hardware
 Software
 Users
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Data
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Database System are available on machines that
range from all the way from personal computers to
the largest mainframe or clusters of mainframes.
In particular, tend to be multi-user; whereas on
small machine tend to be singer user.
 Single User system is a system in which at most
one user can access the database at any given
time.
 Multi user system is a system in which many
users can access the database at the same time.
The data in database – for large systemwill be both integrated and shared.
 Integrated
– Mean the database can be thought of as
a unification of several district files, with
any redundancy among those files
partly or wholly eliminated
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Shared
– Mean the database can be shared among
different users, in the sense that different
users can have access to the same data,
possible even at the same time
(“Concurrent access”).
Hardware
The hardware components of the system
consist of
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The secondary storage volumes used to
hold the stored data, together with the
associated I/O devices, device controllers,
and so forth.
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The hardware processors and associated
main memory that are used to supported
the execution of the database system
software
Software
Database Management System (DBMS)
Data => physically stored
All request for access to the database are handle
by the DBMS
DBMS is thus shielding of database users from
hardware level details
Provides users with a perception of the database
that is elevated somewhat above the hardware
level details.
Support user operations
Database Management
System
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DBMS is a general purpose software
system that facilitates the process of
definition, construction, manipulating,
and sharing databases among various
users and applications.
– Defining a database involves specifying
the data types, structures, and constrains
for the data to be stored in the database.
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Manipulating a database includes such functions
as querying the database to retrieve specific data,
updating the database to reflect changes, and
generating reports from data.
Sharing a database allows multiple users and
programs to access the database concurrently.
Other important functions
– Protection both system protection against hardware or
software malfunction (crash) and Security protection
against unauthorized or malicious access.
– DBMS must be able to maintain the database System
by allowing the system to evolve as requirements change
over time.
User
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Application Programmer
– Responsible for writing database
application programs in some
programming language
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End User
– Access database interactively as just
described, A given user can access the
database via online application program
or user query language
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Database Designers
– Responsible for identifying the data to be stored
in the database and for choosing appropriate
structures to represent and store in database.
– Undertaken before the database is actually
implement.
– It is responsibility of database designers to
communicate with all database user to
understand their requirements, and to come up
with a design that meets users’ requirements.
– Designer may be one of staff of Database
Administrator (DBA)
– Interact with each groups of users and develop
views the database that meet the data and
processing requirements of those groups.
– Final database design must be capable of
supporting the requirements of all user groups.
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Database Administrators: responsible for authorizing
access to the database, for coordinating and monitoring
its use, and for acquiring software and hardware resource
need
Defining the conceptual schema (Logical/conceptual
Database Design)
Defining the internal schema (Physical Database
design)
Liaising with users, to ensure that data they need is
available and to write or help user to write the
external schemas, using the applicable external DDL.
Defining security and integrity constraints
Defining dump/restore schemes
Monitoring performance and responding to changing
requirement.
DATABASE SYSTEM
Users/Programmers
Application Programs/Queries
DBMS
Software
Software to Process
Quires/Programs
Software to Access
Stored Data
Stored Database
Definition
(Meta Data)
Stored
Database
What is a database
By C.J. Date
“a Database is a collection of persistent data that is
used by the application systems of some given
enterprise”
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Elmasri & Navatha
“Database is a collection of related data.
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– Data mean facts that can be recorded and that have
implicit meaning.”
– Database can be any size and varying complexity
– Database may be generated and maintained manually or it
may be computerized.
Why Database
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Compactness: no need for possible
voluminous paper file.
Speed: Machine can retrieve and update
data faster than human
Less drudgery: maintaining files by hand
is eliminated.
Currency: Accurate, up-to-date information
is available on demand at any time.
Protection: Data can be better protected
against unintentional loss and unlawful
Benefits of Database
Approach
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The data can shared
Redundancy can be reduced/controlled
Inconsistency can be avoided
Transaction support can be provided
Integrity can be maintained
Security can be enforced
Conflicting requirements can be balanced
Standard can be enforced
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Controlling redundancy
– Redundancy is storing the same data
multiple times leads to several problems.
Duplication effort
 Storage waste, when same data stored
repeatedly
 File that represent same data may became
inconsistent.
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– Database approach, the views of different
user groups are integrated during
database design. Logical data item in only
one-place in database, Ensure
redundancy, “controlled redundancy”.
Security
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Restricting Unauthorized Access
– Multiple user share large database
– most users will not be authorized to access all information
in the database
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Example : KKU Registration
all database can see by DBA
Students can see/manipulate only
some part of their data
– Type of operation must be controlled
– User/User group are given account number and passwords
to access the data base. DBMS provide a security and
authorization subsystem, DBA uses them to create
account and to specify account restrict.
Example
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Fact(factcode, factname)
Dept(faccode, deptcode, deptname)
Student(id, name, address,
factcode,factname)
Subject(subjcode, subjname, credit)
Teacher(tcode,tname,taddress,factcode
,deptcode,….)
Grade(id,subjcode,year,sem,grade)
Etc.
Integrity
Example
Create table fact( factcode char(4),
factname varchar2(30),
primary key(factcode));
Example 2
Create table dept( factcode char(4),
deptcode char(4),
deptname varchar2(30),
primary key(factcode,deptcode),
foreign key (factcode)
references fact(factcode));
view
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Create view studGrd as select
id,name,subjcode,name,year,sem,grade
from student,grade
where stdent.id = grade.id
Summary
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Define a database system and
database components
Database as a collection of related
data, where data means recorded
facts.
The benefic of the Database system