INTRODUCTION TO INTERNET AND WWW

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UNIT1
INTRODUCTION TO INTERNET AND WWW
1.1INTERNET
The Internet can be defined as:
“A GLOBAL NETWORK CONNECTING MILLIONS OF COMPUTERS.”
It is a network of networks (i.e., interconnection between several autonomous
computers) that carries various information and services, such as E-mail, online chat,
file transfer, and interlinked web pages and other resources of the World Wide Web.
World Wide Web
The World Wide Web gives a graphical, easy – to – navigate interface for looking at
documents on the Internet.
The WORLD WIDE WEB may be defined as:
“A NETWORK OF SERVERS LINKED TOGETHER BY A COMMON PROTOCOL (SET
OF RULES), ALLOWING ACCESS TO MILLIONS OF HYPERTEXT RESOURCES.”
It is also known as WWW, or W3, or simply WEB. It is just a component of the Internet.
A Web is composed of millions of Web pages linked together.
In order to access anything on the Web like information, mail, images, services, etc., the
user has to access a “Web-site”.
WEBSITE
“A WEB-SITE IS A LOCATION ON THE INTERNET ACCESSIBLE BY INPUTTING A
UNIQUE ADDRESS THAT PROVIDES INFORMATION ON A SUBJECT, PERSON, OR
ORGANIZATION.”
A website is a related collection of web files (also known as Web pages).
WEB PAGE
“A WEB PAGE IS A COLLECTION OF INFORMATION BY A PERSON, GROUP OR
AN ORGANIZATION.”

Pages can contain news, images, movies, sounds, etc. These pages can be connected by
providing links (that may be special text or some graphics) called hyperlinks.
HYPERLINKS
“HYPERLINKS ARE UNDERLINED OR BORDERED WORDS AND GRAPHICS THAT
HAVE WEB ADDRESS EMBEDDED IN THEM.”
By clicking on a hyperlink, user can jump to a particular page in a particular website.
1.2 HYPERTEXT
“HYPERTEXT REFERS TO THE TEXT ON A COMPUTER THAT WILL LEAD THE
USER TO OTHER, RELATED INFORMATION ON DEMAND.”
Hypertext represents a relatively different concept of written text. It can be designed to
perform various tasks; for instance when a user “clicks” on it or “hovers” over it, a
bubble with a word definition may appear, a web page on a related subject may load, a
video clip may run, or an application may open.
1.2.1 Idea of Hypertext
Hypertext’s original idea was to take advantage of electronic data processing
to organize large quantities of information that would otherwise swallow up a
reader. The basic hypertext made the information directly accessible.
Augmenting basic hypertext with graphics, more complex user input fields
and dynamically generated documents add considerable power and flexibility.
Hypertext, though still useful for its original goal of organizing large
quantities of information becomes a simple, general – purpose user interface
that fits neatly into the increasingly popular client – server model.
1.2.2 Characteristics of a Good Hypertext
The flexibility of hypertext gives free range to the author’s creativity, but good
hypertext appears to have some common characteristics:
a. Lots of documents. Much of the hypertext’s power comes from its
ability to make large quantities of information accessible.
b.

c. Lots of links. A hypertext document should present the reader with
several links, offering a choice about where to go next.
d.
e. Range of detail. The great advantage of hypertext is that it permits
readers to explore to a breadth and depth that is simply not feasible in
print.
f.
g. Correct Links. A good hypertext should provide a correct link points to
some useful document instead of pointing nowhere.
1.3 HYPERMEDIA
“HYPERMEDIA IS USED AS A LOGICAL EXTENSION OF THE TERM HYPERTEXT IN
WHICH GRAPHICS, AUDIO, VIDEO, PLAIN TEXT AND HYPERLINKS INTERLINK TO
CREATE A GENERALLY NON – LINEAR MEDIUM OF INFORMATION.”
The World Wide Web is a classic example of hypermedia, whereas a non – interactive
cinema presentation is an example of standard multimedia due to the absence of
hyperlinks. Thus contrasts hypermedia with multimedia that may be used to describe
non – linear presentations as well as hypermedia.
1.3.1 Hypermedia Development Tools
Hypermedia may be developed in a number of ways. Any programming tool
can be used to write programs that link data from internal variables and
nodes for external data files.
Multimedia development software such as Adobe Flash, Adobe Photoshop,
etc. may be used to create stand – alone hypermedia applications, with
emphasis on entertainment content.
Some database software such as Visual FoxPro may be used to develop stand
– alone hypermedia applications, with emphasis on educational and business
management.
1.4 HOW THE WEB WORKS
To surf the Web the user needs a Web browser.
“A WEB BROWSER IS AN APPLICATION THAT DISPLAYS THE WEB DOCUMENTS.”

The user first opens a Web browser, and then enters a URL (Uniform Resource Locator)
in the address bar.
“A URL IS THE ADDRESS OF A DOCUMENT THAT A USER NEEDS TO BE ABLE TO
GET HOLD ON.”
After inputting the URL, the protocol determines the address of the server computer that
contains the required document to be opened. Then the connection is established with
the server and a request is sent for the required document. The server in response sends
the requested document to the browser. This can be explained in following steps:
1. Parsing the URL. The browser looks at the URL to determine the address
of the document on Web. It firstly, determines the address i.e., domain
name of the server.
Let us consider a URL:
http://www.microsoft.com/home.asp
The http (“THE HYPERTEXT TRANSFER PROTOCOL DESCRIBES HOW
TO TELL THE SERVER WHICH DOCUMENT TO BE PROVIDED TO THE
USER AND HOW TO RETRIEVE IT.”) determines the address or domain
name of the server to be connected as:
www.microsoft.com
2. Resolving the IP address. The Domain Name System (DNS) executes a
resolver program to determine the IP address corresponding to the given
domain name.
3. Establishing the Connection with the server. After resolving the IP
address, the connection is established the determined server.
4. Sending the request. As the connection is established, the browser
transmits the following request to the server:
“GET/request – URI HTTP/version”
Where version tells the server which http version is used.
5. The server’s response. When the server receives the HTTP request, it
locates the appropriate file and returns it to the client’s browser. In the
above example the requested file is:
Home.asp
6. Downloading the Document. The document returned by the server (be it
an HTML document) is downloaded by the browser and then displayed to
the user.

If the HTML document contains other resources like graphics, sound,
animations, etc. these are downloaded in the similar manner as the HTML
document and then displayed.
7. Connection Termination. As the file or document is downloaded, the
connection with the server is terminated.
1.5 HOW THE WEB BROWSER WORK
The working of the Browser depends on some of the issues like:
a. MIME types
b. Plug – INS, and
c. Helper Applications
These are explained below:
1.5.1 MIME Types
“MULTIPURPOSE INTERNET MAIL EXTENSION (MIME) IS AN INTERNET
STANDARD THAT EXTENDS THE FORMAT OF E-MAIL TO SUPPORT NON – TEXT
ATTACHMENTS AND NON – ASCII CHARACTER SETS.”
Originally, only ASCII text files could be sent via email. Today, an email message may
contain an attachment that consists of virtually any type of file.
Usually ASCII files are referred as text or plain text files and all other files as binary
files. MIME is used to send messages containing another form of media such as
graphics, HTML code, a spreadsheet document, video, voice, and/or a word processor
document attached in addition to text. All that is necessary is that the mailer and the
recipient’s mailer be MIME compliant. If the recipient’s mailer is not MIME
compliant, the files transferred through attachment will not be displayed properly
with all features of the document.
MIME was originally developed as an extension to the Internet mail protocol that allows
for the inclusion of multimedia in mail messages.
BASIC IDEA OF MIME is transmission of text files alongwith additional Binary data.
Each MIME type is composed of two parts that indicate the data type and subtype in
the following format:
Content – type : type / subtype

Where type can be image, audio, text, video, application, message, or extension – token;
and
subtype gives the specifics of the content.
Some samples of the types are listed below:
text / html application / x – pdf
video / quicktime image / gif
image / jpeg audio / x – wav
When a web server delivers a file, the header information is intercepted by the browser
and questioned. The MIME type is specified by the Content – type HTTP response field.
For example, if a browser receives a basic HTML file, the text / html value in the
Content – type header indicates what the browser should do.
The browser first would read the HTML being delivered and then retrieve any other
objects, such as GIF images, sound files, Flash files, Java Applets, and so on, that
would result in another request to the server.
If a browser encountered something like this:
<IMG src = “images / logo.gif” alt = “demo company” height = “100” width =
“200”>
1.5.2 Plug – INS and Helper Applications
To get the most from the browser, the user need to configure it to handle the
different types of files that are used on the web. Plug-in's and helper applications
are two different ways to view these files. Plug-in's are special programs designed to
view documents in the browser. Helper applications can be any program on your
computer.
1.5.2.1 PLUG - INS
“PLUG – INS ARE SMALL PROGRAMS THAT EXTEND THE BROWSER TO
SUPPORT NEW FUNCTIONALITY DESIGNED TO VIEW DOCUMENTS IN THE
BROWSER.”
Users must locate and download plug – INS, install them, and occasionally even
restart their browsers.

The plug – INS can be included in Web pages by using the <embed> or <object>
tags. Typically, the <embed> syntax is used, but the <object> syntax is preferred
method because it is a part of the XHTML specification, and will, therefore, validate.
1. <EMBED> SYNTAX FOR PLUG – INS
In general embed element takes src attribute to specify the URL of the included
binary object. The height and width attributes often are used to indicate the pixel
dimensions of the included object, if it is visible. For example,
<EMBED src = “welcome.avi” height = “100” width = “100”></EMBED>
The <embed> tag displays the plug – in as part of the HTML / XHTML document.
Some of the other attributes used in embed element are:
(i) align: used to align the object relative to the page and allow text to flow
around the object.
(ii) hspace and vspace: used to set the buffer region, in pixels, between the
embedded objects and the surrounding text.
(iii) Border: used to set a border for the plug – in, in pixels.
Values for height and width should always be set, unless the hidden attribute is
used. Setting the hidden attribute to true in an <embed> tag causes the plug – in
to be hidden and overrides any height and width settings.
1.1 CUSTOM PLUG – IN ATTRIBUTES
In addition to standard attributes, plug – INS might have custom attributes to
communicate specialized information to the plug – in code. For example, a movie
player plug – in may have a loop attribute to indicate how many times to loop the
movie.
1.2 ATTRIBUTES FOR INSTALLATION OF PLUG – INS
If embedded data in a web page has no associated plug – in, the user will need to
install a plug – in to address it. So the user should set the pluginspage attribute
equal to a URL that indicates the instructions for Installing the needed plug – in.
The user can use pluginurl attribute also in place of pluginspage attribute.
2. <NOEMBED>
Some browsers don’t understand the <embed> tag. So the <noembed> tag enables
the user to provide some alternative text or marked – up content. For example,

<EMBED src = “welcome.avi” height = “100” width = “100” / >
<NOEMBED>
<img src = “welcome.gif” alt = “Welcome to Demo Company” / >
< / NOEMBED>
One potential problem with the <noembed> approach occurs when a browser
supports plug – INS but locks the specific plug – in to deal with the included binary
object. In this case, the user is presented with a broken puzzle piece icon or a
similar icon, and then is directed to a page to download missing plug – in.
3. <OBJECT> SYNTAX FOR PLUG – INS
The primary attribute of the <object> element when referencing plug – INS is data,
which represents the URL of the object’s data and is equivalent to the src attribute
of <embed>.
type: attribute represents MIME type of the object’s data.
codebase: attribute is similar to pluginspage attribute representing the URL of the
plug – in.
classid: attribute is used to specify the URL to use to install the plug – in just like
codebase.
id: attribute is used to set the name of the object for scripting.
For example,
<OBJECT data=“click.wav” type=“audio / wav” height = “60” width = “144” autostart
= “false”>
<B> Sorry, No Live Audio Installed…< / B>
< / OBJECT>
DRAWBACKS OF PLUG - INS
1 Although plug – INS can go a long way toward extending the possible capabilities
of a browser, the technology does have its drawbacks:

2 Users must locate and download plug – INS, install them, and occasionally even
restart their browsers.
3 Even if installation were not such a big problem, plug – INS are not available on
every machine.
4 An executable program, or binary, must be created for each particular operating
system.
5 Because of the machine – specific approach, many plug – INS work only on
Windows – based systems.
6 Each plug – in installed on system is a persistent extension to the browser, and
takes up memory and disk space.
BENEFITS OF PLUG - INS
The benefit of plug – INS is that they can be well integrated into web pages. These
can be included by using the <embed> or <object>.
1.5.2.2 HELPER - APPLICATIONS
“A HELPER APPLICATION IS AN EXTERNAL VIEWER PROGRAM LAUNCHED
TO DISPLAY CONTENT RETRIEVED USING A WEB BROWSER.”
Some common examples include Windows Media Player and QuickTime Player for
playing streaming content.
Unlike a plugin (whose full code is included into browser code), a small line is
added to the browser code to tell it to open a certain helper application in case it
encounters a certain file format.
Common helper applications include RealAudio, which allows browsers to play live
sound tracks such as radio broadcasts or recorded lectures; Acrobat;
For local files and other files for which a web browser does not get a content type
from the server, user can use a helper application entry to give a specific MIME
Type to files with a specific extension. To do this, user just needs to create an entry
in Edit/Preferences/Helper Applications, enter the MIME Type that he want in the
Type field, and enter the extensions in the extension field. The rest can be left at the
default values.

INTRODUCTION TO INTERNET AND WWW

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