Mapping

Mapping is a process of converting one level to another level. In this process,the data
at one level is related to the data and another level.

The conceptual/internal mapping defines the correspondence between the conceptual view and
stored database. It specifies how conceptual records and fields are represented at the internal level
if the structure of stored database is changed, then the conceptual mapping must be changed
accordingly so that the conceptual schema can remain consistent. It is the responsibility
of DBA to manage such change.

Read More

Logical , Internal Or Physical level

Logical or conceptual Level
This is the middle level view in three level architecture. The logical or conceptual
level describes the data stored in database. It contains the definition of the data to be stored 
in the database. It also contains the rules and information about the structure and type of 
data. It is the complete description of data stored in database. That is why it is also known as a community view of the database.This level contains the logical structure of entire database as seen. It hides the details of physical storage instruction physical Storage  structure

The conceptual level supports each external view. It means that any data require by
any user must be available from conceptual view. The conceptual model is comparatively 
constant. Dba designs a conceptual mode to fulfill the present and future requirements of
the organization. If there is any charge in external model, The conceptual model should 
be able to accomodate that change. It is important because any changes in the conceptual 
models requires a lot of effort. It also effects other views or levels of the database. the conceptual level is described in conceptual schema. There is only one schema for one database.

Internal Or Physical level

Internal level is responsible to store data on storage media. It describe the physical 
representation of database on computer. It describes how the data is stored in database . It 
covers the data structures and file organization used to store data on storage devices.
Internal and physical levels are normally considered to be same. But there is a slight method 
is implemented by operating systems. DBMS partially decides the way data is stored on the Disk. The binary storage This decisions is based in the specifications of DBA. Additionally 
DBMS adds information to the data to be stored For example it selects a specific files 
organization for storing data on the disk. It also applies different data encryption
algorithms to implement security on the data.

It performs a storage space utilization to consume minimum space for storing data 
The data compressions can be performed for this purpose. It also applies 
different data encryption algorithms to implement security on the data.

The records at internal level are presented according to the format of schema difinition
but the data is not in the record format at physical level. It is in character format. The rules 
specified by the schema of record are not enforced at physical level. Data is managed 
by operating system at physical level.

Read More

three level architecture and external level

 Three level architecture
Database Task group developed and published a proposal for a standard vocabulary
and architecture for database system in 1971. It was appointed by a conference
on database system and Languages. The Standards Planning and requirement
committee of American National standards institute committee on information processing
developed and published a similar vocabulary and architecture in 1975.

The result of these reports was the three level architecture. The three level architecture
is the basic of modern database architecture. Database can be viewed at three levels. The three
levels are depicted by three models known as three level schema. The models refers to the structure
of the database not the data stored on it. The parmanent structure of database is known as
intension of database or schema. The data stored at a given time is known as extension of database
or database instance.

The Intension of a database should not be changed once it has been defined. This is because a small
change in the intension of database may requires many changes to the data stored in database
. The extension of database is performed according to the rules defined in the intension of database.

The schema is used to store definition of the structure of the database. It can be any thing
like a single intity or the whole organization. Three level architecture define different
schemes are stored to the different levels to isolate the details of different levels from
one another.
external level
The external level consists of different external views of a database. Each external
view is the view of a particular user about the system. Different users conceive
the system in the different ways. Each users  is interested in one part of the system and
ignores other parts. One user may not be aware of the whole system at all.

Different views may have different representations of the same data. For example,one
user may think that dates are stored in form. Another user may think they are represented
as year/month/day.

Some views might include virtual or calculated data. Virtual data is the data that is not actually
stored in database but created when needed. For Example, the product name and its
price can be used to stored in database. The total bill can be created as and when desired
 so Similarly can be calculated when result card is prepared.

Read More

The internet

The internet is a collection of Milions computers around the World That are all connected to one another.It is
a global network of computers.These Computers are connected through different telecommunications links
like Phone Lines ,Fiber optic Lines, Satellites and wireless connections
internet is used to find information stored on computer called hosts or sevens.These
computers use a common protocol Called TCP/IP for communication.TCP/IP stands
for transmission Control Protocol/Internet Protocol.

No government or organization is the owner of internet. Many people,organizations,universities
and research agencies participate to run Internet.Everyone who has access to the Internet can get
information from the Internet.Millions of people have access to Internet.

Working of Internet
The network is used by the Computers to communicate with cable Modem.These devices
Communicate with the server of Internet Server Provider.
A user computer is usually connected with ISP using phone lines,DSL or cable Modem
 The computers connected to the Internet exchange data and information using servers
and clients.A client computer accesses data,information and services from different
servers.The server computer are also called host computers.

Positive aspects of Internet in society

The positive effects of the Internet of the society are as follows:
internet has converted this world into a global village.people are connected with one another
using the internet with one another using internet.It has provided more opportunities
of interaction.It also enables people to understand the views of one another.
Internet contains information on all types of topics.people can search information on any topic any Article.Search engine is used to search information on Internet .Easy access to
information has enabled people to be informed.
The uses of internet has provided many comforts for society.People can perform their Duties
easily.

Negative aspects of Internet in Society
Internet contains a large numbers of websites.These websites contains such material
that is against the moral values of our society.
Internet is the the most important source of spreading computer viruses.People spread viruses
using Internet and Emails.many websites also contain different viruses that are copied
to the computers when the users visits to These websites.And it is also The wastage of time because a many young waste their time on Chatting.

Read More