Relational
Database Management Systems
Airline
Reservation System
CLIENT/SERVER SYSTEM :
A client/server system is a
distributed systems in which,
(a) some sites are client sites
and others are serer sites
(b) all data resides at the
server sites
(c) all applications execute
at the client sites
The term ‘client/server’
refers primarily to an architecture,
or logical division of responsibilities
, the client is the application
(also known as the frontend),
and the server is the DBMS (also
known as the backend).
A client/server system can
be thought of as a distributed
system in which all requests
originate at one site and all
processing is performed at another.
In practice the client site
might well have its own local
databases, but those databases
will not play a direct part
in the client/server arrangement
as such.
Client/Server provides a low-priced
robust solution to user requirements.
This approach permits downsizing
production subsystem while allowing
the clients and servers the
necessary tools and facilitate
to control, manage and tune
the environment in which they
operate.
Most client/server solution
are also very attentive in matters
of security. Access to any resources
can be defines to the file level,
with such access being controlled
through identification and authorization.
Logically defined closed use
groups can be setup to enable
the enhancing of security measures
by network administrations.
It allows the database management
including security, performance,
backup, server enforced integrity
to be part of the database machine
avoiding the requirement to
write large number of redundant
piece of code dealing with database
field validation and referential
integrity.
The successful organizations
have to be marked drives and
competitive in the times to
come, and they will use Client/Server
computing as the enabling technology
to add values to their business.
Powerful workstations will be
available to all end users to
be used as clients to access
the information on the servers
which are distributed globally.
The networks of the future will
support much higher bandwidth
by using technologies like corporate
networks will cut across the
boundaries of cities or even
countries and they will be connected
to major networks around the
worlds.
E-R DIAGRAM :
E-R Diagram constitute a technique
for representing the logical
structure of a database in a
pictorial manner. This analysis
is then used to organize data
as a relation, normalising relation
and finally obtaining a relation
database.
Entities : Which specify distinct
real-world items in an application.
Properties (or): Which specify
properties of an entity and
relationships.
Attributes
Relationships : Which connect
entities and represent meaningful
dependencies between them.
NORMALIZATION
:
The basic objective of normalization
is to be reduce redundancy which
means that information is to
be stored only once. Storing
information several times leads
to wastage of storage space
and increase in the total size
of the data stored.
If a Database is not properly
designed it can gives rise to
modification anomalies. Modification
anomalies arise when data is
added to, changed or deleted
from a database table. Similarly,
in traditional databases as
well as improperly designed
relational databases, data redundancy
can be a problem. These can
be eliminated by normalizing
a database.
Normalization is the process
of breaking down a table into
smaller tables. So that each
table deals with a single theme.
There are three different kinds
of modifications of anomalies
and formulated the first, second
and third normal forms (3NF)
is considered sufficient for
most practical purposes. It
should be considered only after
a through analysis and complete
understanding of its implications.
FIRST NORMAL FORM (1NF)
:
This form also called as a
“flat file”. Each
column should contain data in
respect of a single attributes
and no two rows may be identical.
To bring a table to First
Normal Form, repeating groups
of fields should be identified
and moved to another table.
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