–2/”>a >DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”>
Definition of , search tools, web browsers, e-mail and search engines. IT applications: E-cards, E- shopping, E-Commerce.
- INTERNET
- The is a global Network of billions of computers and other electronic devices. With the , it's possible to access almost any information, communicate with anyone else in the world, and do much more.
- It's important to realize that the is a global network of physical cables, which can include copper telephone wires, TV cables, and fiber optic cables. Even wireless connections like Wi-Fi and 3G/4G rely on these physical cables to access the .
- On visiting a website, the computer sends a request over these wires to a server. A server is where websites are stored, and it works a lot like computer's hard drive. Once the request arrives, the server retrieves the website and sends the correct data back to computer.
- The World Wide Web—usually called the Web for short—is a collection of different websites you can access through the . A website is made up of related text, images, and other Resources. Websites can resemble other forms of media—like newspaper articles or television programs—or they can be interactive in a way that's unique to computers.
- The purpose of a website can be almost anything: a news platform, an advertisement, an online library, a forum for sharing images, or an educational site.
- WEB BROWSER
- Web Browser is an application Software that allows us to view and explore information on the web. In other words, a browser is a software program created as a simplified means to present and explore content on the World Wide Web. These pieces of content, including pictures, Videos, and web pages, are connected using hyperlinks and classified with Uniform Recourse Identifiers (URLs).
- There have been many different web browsers that have come and gone over the years. The first, named WorldWideWeb (later changed to Nexus), was invented by Tim Berners-Lee in 1990. However, the first graphical browser and widely used browser that help bring popularity to the was NCSA Mosaic.
- List of current browsers
|
Browser |
Vendor |
|
Explorer |
Microsoft |
|
Google Chrome |
|
|
Mozilla Firefox |
Mozilla |
|
Netscape Navigator |
Netscape Communications Corp. |
|
Opera |
Opera Software |
|
Safari |
Apple |
|
Sea Monkey |
Mozilla Foundation |
|
K-meleon |
K-meleon |
- Email is a service which allows us to send the message in electronic mode over the internet. It offers an efficient, inexpensive and real time mean of distributing information among people.
E-Mail Address
- Each user of email is assigned a unique name for his email account. This name is known as E-mail address. Different users can send and receive messages according to the e-mail address.
- E-mail is generally of the form username@domainname. For example, webmaster@tutorialspoint.com is an e-mail address where webmaster is username and tutorialspoint.com is domain name.
- The username and the domain name are separated by @ (at) symbol.
- E-mail addresses are not case sensitive.
- Spaces are not allowed in e-mail address.
E-mail Message Components
- E-mail message comprises of different components: E-mail Header, Greeting, Text, and Signature.
E-mail Header
- The first five lines of an E-mail message is called E-mail header. The header part comprises of following fields:
- From
- Date
- To
- Subject
- CC
- BCC
FROM
The From field indicates the sender’s address i.e. who sent the e-mail.
DATE
The Date field indicates the date when the e-mail was sent.
TO
The To field indicates the recipient’s address i.e. to whom the e-mail is sent.
SUBJECT
The Subject field indicates the purpose of e-mail. It should be precise and to the point.
CC
CC stands for Carbon copy. It includes those recipient addresses whom we want to keep informed but not exactly the intended recipient.
BCC
BCC stands for Black Carbon Copy. It is used when we do not want one or more of the recipients to know that someone else was copied on the message.
Greeting
Greeting is the opening of the actual message. Eg. Hi Sir or Hi Guys etc.
Text
It represents the actual content of the message.
Signature
This is the final part of an e-mail message. It includes Name of Sender, Address, and Contact Number.
E-mail System
E-mail system comprises of the following three components:
- Mailer
- Mail Server
- Mailbox
Mailer
It is also called mail program, mail application or mail client. It allows us to manage, read and compose e-mail.
Mail Server
The function of mail server is to receive, store and deliver the email. It is must for mail servers to be sunning all the time because if it crashes or is down, email can be lost.
Mailboxes
Mailbox is generally a folder that contains emails and information about them.
E-mail Protocols are set of rules that help the client to properly transmit the information to or from the mail server. Here in this tutorial, we will discuss various protocols such as SMTP, POP, and IMAP.
SMPTP
SMTP stands for Simple Mail Transfer Protocol. It was first proposed in 1982. It is a standard protocol used for sending e-mail efficiently and reliably over the internet.
Key Points:
- SMTP is application level protocol.
- SMTP is connection oriented protocol.
- SMTP is text based protocol.
- It handles exchange of messages between e-mail servers over TCP/IP network.
- Apart from transferring e-mail, SMPT also provides notification regarding incoming mail.
- When you send e-mail, your e-mail client sends it to your e-mail server which further contacts the recipient mail server using SMTP client.
- These SMTP commands specify the sender’s and receiver’s e-mail address, along with the message to be send.
- The exchange of commands between servers is carried out without intervention of any user.
- In case, message cannot be delivered, an error report is sent to the sender which makes SMTP a reliable protocol.
IMAP
IMAP stands for Mail Access Protocol. It was first proposed in 1986. There exist five versions of IMAP as follows:
- Original IMAP
- IMAP2
- IMAP3
- IMAP2bis
- IMAP4
Key Points:
- IMAP allows the client program to manipulate the e-mail message on the server without downloading them on the local computer.
- The e-mail is hold and maintained by the remote server.
- It enables us to take any action such as downloading, delete the mail without reading the mail.It enables us to create, manipulate and delete remote message folders called mail boxes.
- IMAP enables the users to search the e-mails.
- It allows concurrent access to multiple mailboxes on multiple mail servers.
POP
POP stands for Post Office Protocol. It is generally used to support a single client. There are several versions of POP but the POP 3 is the current standard.
Key Points
- POP is an application layer internet standard protocol.
- Since POP supports offline access to the messages, thus requires less internet usage time.
- POP does not allow search facility.
- In order to access the messaged, it is necessary to download them.
- It allows only one mailbox to be created on server.
- It is not suitable for accessing non mail data.
- POP commands are generally abbreviated into codes of three or four letters. Eg. STAT.
- Comparison between POP and IMAP
|
S.N. |
POP |
IMAP |
|
1 |
Generally used to support single client. |
Designed to handle multiple clients. |
|
2 |
Messages are accessed offline. |
Messages are accessed online although it also supports offline mode. |
|
3 |
POP does not allow search facility. |
It offers ability to search emails. |
|
4 |
All the messages have to be downloaded. |
It allows selective transfer of messages to the client. |
|
5 |
Only one mailbox can be created on the server. |
Multiple mailboxes can be created on the server. |
|
6 |
Not suitable for accessing non-mail data. |
Suitable for accessing non-mail data i.e. attachment. |
|
7 |
POP commands are generally abbreviated into codes of three or four letters. Eg. STAT. |
IMAP commands are not abbreviated, they are full. Eg. STATUS. |
|
8 |
It requires minimum use of server resources. |
Clients are totally dependent on server. |
|
9 |
Mails once downloaded cannot be accessed from some other location. |
Allows mails to be accessed from multiple locations. |
|
10 |
The e-mails are not downloaded automatically. |
Users can view the headings and sender of e-mails and then decide to download. |
|
10 |
POP requires less internet usage time. |
IMAP requires more internet usage time. |
- Search Engine and Search Tools
Search Engine refers to a huge Database of internet resources such as web pages, newsgroups, programs, images etc. It helps to locate information on World Wide Web.
User can search for any information by passing query in form of keywords or phrase. It then searches for relevant information in its database and return to the user.
Search Engine Components
Generally there are three basic components of a search engine as listed below:
- Web Crawler
- Database
- Search Interfaces
Web crawler
It is also known as spider or bots. It is a software component that traverses the web to gather information.
Database
All the information on the web is stored in database. It consists of huge web resources.
Search Interfaces
This component is an interface between user and the database. It helps the user to search through the database.
Search Engine Working
Web crawler, database and the search interface are the major component of a search engine that actually makes search engine to work. Search engines make use of Boolean expression AND, OR, NOT to restrict and widen the results of a search. Following are the steps that are performed by the search engine:
- The search engine looks for the keyword in the index for predefined database instead of going directly to the web to search for the keyword.
- It then uses software to search for the information in the database. This software component is known as web crawler.
- Once web crawler finds the pages, the search engine then shows the relevant web pages as a result. These retrieved web pages generally include title of page, size of text portion, first several sentences etc.
These search criteria may vary from one search engine to the other. The retrieved information is ranked according to various factors such as frequency of keywords, relevancy of information, links etc.
- User can click on any of the search results to open it.
Search Engine Processing
Indexing Process
Indexing process comprises of the following three tasks:
- Text acquisition
- Text transformation
- Index creation
Text Acquisition
It identifies and stores documents for indexing.
Text Transformation
It transforms document into index terms or features.
Index Creation
It takes index terms created by text transformations and create data structures to support fast searching.
Query Process
Query process comprises of the following three tasks:
- User interaction
- Ranking
- Evaluation
User Interaction
It supporst creation and refinement of user query and displays the results.
Ranking
It uses query and indexes to create ranked list of documents.
Evaluation
It monitors and measures the effectiveness and efficiency. It is done offline.
Examples
Following are the several search engines available today:
|
Search Engine |
Description |
|
|
It was originally called BackRub. It is the most popular search engine globally. |
|
Bing |
It was launched in 2009 by Microsoft. It is the latest web-based search engine that also delivers Yahoo’s results. |
|
Ask |
It was launched in 1996 and was originally known as Ask Jeeves. It includes support for match, dictionary, and conversation question. |
|
AltaVista |
It was launched by Digital Equipment Corporation in 1995. Since 2003, it is powered by Yahoo technology. |
|
AOL.Search |
It is powered by Google. |
|
LYCOS |
It is top 5 internet portal and 13th largest online property according to Media Matrix. |
|
Alexa |
It is subsidiary of Amazon and used for providing website traffic information. |
Search Tools
There are three basic types of search tools that most people use to find what they are looking for on the Web.
- Search Engines
- Subject Directories
- Meta Search Tools
None of these search tools allow to search the entire Web; that would be an almost impossible task. However, one can use these Web search tools to scour different parts of the Web, obtain different types of information, and broaden the Web search horizons.
Search the Web with Search Engines
Search engines are large, spider(software programs) created databases of web pages that help searchers find specific information on any given subject. When anyone type in a keyword or phrase and the search engine retrieves pages that correspond to the search query.
Search results gathered from these search engines are not always relevant to the keywords entered since these engines are not intuitive and cannot infer dynamically what it is, one might be searching for (although results are getting better all the time). This is why it's important to learn how to search as efficiently as possible using such techniques as Boolean search, or basic Google search techniques.
Interpretation of relevancy is different in each search engine. Many search engineshave included categories to direct users to more relevant sites based on these particular topics.
Search the Web with Subject Directories
Subject directories, in general, are smaller and selective that search engines. They use categories to focus the search, and their sites are arranged by categories, not 6.3-42 24.9-48.3 48.6-11.4 42.9-11.4 132.3-11.4 132.3s0 89.4 11.4 132.3c6.3 23.7 24.8 41.5 48.3 47.8C117.2 448 288 448 288 448s170.8 0 213.4-11.5c23.5-6.3 42-24.2 48.3-47.8 11.4-42.9 11.4-132.3 11.4-132.3s0-89.4-11.4-132.3zm-317.5 213.5V175.2l142.7 81.2-142.7 81.2z"/> Subscribe on YouTube