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WSD - MSc-IT 2nd
sem
The Web vs. the Internet
There is an often-overlooked distinction between the Web and the
Internet. The linebetween the two is often blurred, partially
because theWeb is rooted in the fundamentalprotocols associated
with the Internet. Today, the lines are even more blurred,
asnotions of the Web go beyond the boundaries of pages delivered to
Web browsers,
THE ORIGINS OF THE WEB
Tim erners-!ee originally promoted theWorldWideWeb as a virtual
library, adocumentcontrol system for sharing information resources
among researchers. "nlinedocuments could be accessed via a uni#ue
document address, a Universal ResourceLocator $%&!'. These
documents could be cross-referenced via hypertext links.
Hypertext
Ted (elson, father of the )anadu *ro+ect, coined the term
hypertet over yearsago, as a way of describing non-se#uential
writing/tet that branches and allowschoice to the reader. %nlike
the static tet of print media, it is intended for use withan
interactive computer screen. It is open, 0uid and mutable, and can
be connected toother pieces of hypertet by links.The term was
etended under the name hypermedia to refer not only to tet, but
toother media as well, including graphics, audio, and video.
1owever, the original termhypertet persists as the label for
technology that connects documents and informationresources through
links.
Internet Protocols are the Founat!on o" Web Technolo#y
It should be noted that the Web did not come into eistence in a
vacuum. The Web isbuilt on top of core Internet protocols that had
been in eistence for many years prior tothe Webs inception.
%nderstanding the relationship between Web technology and
theunderlying Internet protocols is fundamental to the design and
implementation of trueWeb applications. In fact, it is the
eploitation of that relationship that distinguishesa Web page or
Web site from a Web application.
FRO$ WEB P%GES TO WEB SITES
The eplosively eponential growth of the Web can at least
partially be attributed toits grass roots proliferation as a tool
forpersonal publishing. The fundamentaltechnologybehind the Web is
relatively simple. 2 computer connected to the Internet,running a
Web server, was all that was necessary to serve documents. oth
34&(and the (ational 3enter for 5upercomputer 2pplications
$(352' at the %niversity
of Illinois had developed freely available Web server software.
2 small amount ofHTML knowledge $and the proper computing
resources' got you something thatcould be called a Web site.
FRO$ WEB SITES TO WEB %PP&I'%TIONS
Initially, what people shared over the Internet consisted mostly
of static informationfound in 6les. They might edit these 6les and
update their content, but there werefew truly dynamic information
services on the Internet. 7ranted, there were a few
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eceptions8 search applications for 6nding 6les found on 9T*
archives and 7opherservers: and services that provided dynamic
information directly, like the weather,or the availability of cans
from a soda dispensing machine. $"ne of the 6rst Webapplications
that Tim erners-!ee demonstrated at 34&( was a gateway for
lookingup numbers from a phone book database using a Web
browser.'
(e)n!t!on o" a Web %ppl!cat!on
What is a Web application; y de6nition, it is something more
than +ust a Web site.
It is a client/server application that uses a Web browser as its
client program, and performsan interactive service by connecting
with servers over the Internet $or Intranet'.2 Web site simply
delivers content from static 6les. 2 Web application
presentsdynamically tailored content based on re#uest parameters,
tracked user behaviors, andsecurity considerations.
Web pa#e es!#n resources
9or Web page design, there is a variety of books available.
eyond the tutorialbooks that purport to teach 1T
Web appl!cat!on es!#n resources
When we eamined the current literature available on the sub+ect
of Web applicationdevelopment, we found there were three main
categories of books currentlyavailable.
> Technical (vervie)s. The 6rst category is the technical
overvie). These booksare usually at a very high level, describing
terminology and technology in broadterms. They do not go into
enough detail to enable the reader to design andbuild serious Web
applications. They are most often intended for managers
andeecutives who want a surface understanding of the terminology
without goingtoo deeply into speci6c application development
issues. 9re#uently, they attemptto cover technology in huge
brushstrokes, so that you see books whose focus is
simply =ava, )
> $n!epth Technical Resources. The second category is
comprised of in-depthtechnical resources for developing Web
applications using speci6c platforms.
The books in this category provide in-depth coverage of very
narrow areas,concentrating on the how-tos of using a particular
language or platform without
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eplaining what is going on under the hood. While such books may
beuseful in teaching programmers to develop applications for a
speci6c platform,they provide little or no information about the
underlying technologies, focusinginstead on the platform-speci6c
implementation of those technologies. 5houlddevelopers be called
upon to rewrite an application for another platform, theknowledge
they ac#uired from reading these books would rarely be
transferableto that new platform.
7iven the way Web technology changes so rapidly, todays platform
of choice
is tomorrows outdated legacy system. When new development
platforms emerge,developers without a fundamental understanding of
the inner workings of Webapplications have to learn their inner
workings from the ground up, becausethey lacked an understanding of
6rst principles/of what the systems they wrotereally did. Thus, the
ability to use fundamental technological knowledge acrossplatforms
is critical.
> Re%erence #ooks. These form a third category. 5uch books
are useful, naturally,as references, but not for the purpose of
learning about the technology.What we found lacking was a book that
provides an in-depth eamination ofthe basic concepts and general
principles of Web application development. 5uch
Pr!nc!ples o" *eb appl!cat!on es!#n
What do we mean when we discuss the general principles that need
to be understoodto properly design and develop Web
applications;
We mean the core set of protocols and languages associated with
Web applications.This includes, of course, HTT* $HyperText Trans%er
*rotocol' and HTML$HyperText Markup Language', which are
fundamental to the creation andtransmissionof Web pages. It also
includes the older Internet protocols like Telnet and+T*, protocols
used for message transfer like ,MT* and $M&*, plus
advancedprotocols
and languages like-ML. 2dditionally, it includes knowledge of
databasesand multimedia presentation, since many sophisticated Web
applications make useof these technologies etensively.
The ideal Web application architect must in some sense be a +ack
of all trades.*eople who design Web applications must understand
not only 1TT* and 1T
=ava5cript, )
Be"ore the Web+ T'P,IP
In this chapter, we eamine the core Internet protocols that make
up the T.*/$*protocol suite, which is the foundation for Web
protocols, discussed in the netchapter. We begin with a brief
historical overview of the forces that led to thecreation of
T3*@I*. We then go over the layers of the T3*@I* stack, and show
wherevarious protocols 6t into it. "ur description of the
client-server paradigm used by
T3*@I* applications is followed by a discussion of the various
T3*@I* application
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services, including Telnet, electronic mail, message forums,
live messaging, and6le servers.
The cl!ent,server para!#-
T3*@I* applications tend to operate according to the
client/server paradigm. Thissimply means that, in these
applications, servers $also called services and daemons,depending
on the language of the underlying operating system' eecute by$A'
waiting for re#uests from client programs to arrive, and then $B'
processingthose re#uests.
Telnet
The Telnet protocol operates within the 2pplication layer. It
was developed tosupport (etwork Cirtual Terminal functionality,
which means the ability to log into a remote machine over the
Internet. The latest speci6cation for the Telnet protocolis de6ned
in Internet &93 DEF.
&emember that before the advent of personal computers,
access to computingpower was limited to those who could connect to
a larger server or mainframecomputer, either through a phone dialup
line or through a direct local connection.Whether you phoned in
remotely or sat down at a terminal directly connected tothe server,
you used a command-line interface to log in. Gou connected to a
singlesystem and your interactions were limited to that system.
With the arrival of Internet services, you could use the Telnet
protocol to login remotely to other systems that were accessible
over the Internet. 2s mentionedearlier, Telnet clients are
con6gured by default to connect to port B on the servermachine, but
the target port number can be over-ridden in most client
programs.
This means you can use a Telnet client program to connect and
talk to anyT3*server by knowing its address and its port
number.
Electron!c -a!l
4lectronic mail, or email, was probably the 6rst killer app in
what we now callcyberspace. 5ince the net had its roots in military
interests, naturally the tone ofelectronic mail started out being
formal, rigid, and business-like. ut once the bodyof people using
e-mail epanded, and once these people realiHed what it could beused
for, things lightened up #uite a bit.
SMTP
,MT* stands for ,imple Mail Trans%er *rotocol. 2s an application
layer protocol,5
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POP
*(*, the *ost (2ce *rotocol, gives users direct access to their
e-mail messagesstored on remote systems. *(*3 is the most recent
version of the *"* protocol.
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referring to the system as a World Wide Web.
y the end of AJJ, erners-!ee had implemented a server and a
command-linebrowser using the initial version of the HyperText
Trans%er *rotocol $1TT*' thathe designed for this system. y the
middle of AJJA, this server and browser weremade available
throughout 34&(. 5oon thereafter, the software was made
availablefor anonymous 9T* download on the Internet. Interest in
1TT* and the Web grew,and many people downloaded the software. 2
newsgroup, comp7in%osystems7))),was created to support discussion
of this new technology.
=ust one year later, at the beginning of AJJ, there were about E
dierent sitesrunning 1TT* servers. This number grew to B by the
autumn of that year. Inaddition, since the speci6cation for the
1TT* protocol was openly available
B/I&(ING B&O'0S OF THE WEB
There were three basic components devised by Tim erners-!ee
comprising theessence of Web technology8
A. 2 markup language for formatting hypertet documents.B. 2
uniform notation scheme for addressing accessible resources over
the network.
. 2 protocol for transporting messages over the network.
The markup language that allowed cross-referencing of documents
via hyperlinks wasthe HyperText Markup Language $1T
%nderstanding of 1TT* is +ust as critical in maintaining comple
applications.Gou will realiHe it the 6rst time you try to analyHe
and troubleshoot an elusiveproblem. %nderstanding the 1TT* messages
passed between servers, proies andbrowsers leads to deeper insights
into the nature of underlying problems.
THE /NIFOR$ RESO/R'E &O'%TOR
Tim erners-!ee knew that one piece of the Web puHHle would be a
notation schemefor referencing accessible resources anywhere on the
Internet. 1e devised thisnotational
scheme so that it would be 0eible, so that it would be
etensible, and so thatit would support other protocols besides
1TT*. This notational scheme is knownas the URL or Uni%orm Resource
Locator.
F/N(%$ENT%&S OF HTTP
1TT* is the foundation protocol of the World Wide Web. It is
simple, which isboth a limitation and a source of strength.
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world by storm while more advanced and sophisticated protocols
never realiHedtheir potential.
1TT* is an application level protocol in the T3*@I* protocol
suite, using T3*as the underlying Transport !ayer protocol for
transmitting messages. Thefundamentalthings worth knowing about the
1TT* protocol and the structure of 1TT*messages are8
A. The 1TT* protocol uses the re9uest/response paradigm, meaning
that an 1TT*client program sends an 1TT* re#uest message to an 1TT*
server, which returnsan 1TT* response message.
B. The structure of re#uest and response messages is similar to
that of e-mailmessages:they consist of a group of lines containing
message headers, followed bya blank line, followed by a message
body.
. 1TT* is a stateless protocol, meaning that it has no eplicit
support for thenotion of state. 2n 1TT* transaction consists of a
single re#uest from a clientto a server, followed by a single
response from the server back to the client.In the net few
sections, we will elaborate on these fundamental aspects of the
1TT* protocol.
HTTP servers1 bro*sers1 an prox!es
Web servers and browsers echange information using 1TT*, which
is why Webservers are often called 1TT* servers. 5imilarly, Web
browsers are sometimesreferred to as 1TT* clients, but their
functionality is not limited to 1TT* support.It was Tim erners-!ees
intent that web browsers should enable access to a widevariety of
content, not +ust content accessible via 1TT*. Thus, even the
earliestweb browsers were designed to support other protocols
including 9T* and 7opher.
Today, web browsers support not only 1TT*, 9T*, and local 6le
access, but e-mailand netnews as well.
1TT* proies are programs that act as both servers and clients,
making re#ueststo web servers on behalf of other clients. *roies
enable 1TT* transfers across6rewalls. They also provide support for
caching of 1TT* messages and 6lteringof 1TT* re#uests. They also
6ll a variety of other interesting roles in compleenvironments.
When we refer to 1TT* clients, the statements we make are
applicable tobrowsers, proies, and other custom 1TT* client
programs.
Web Bro*sers
In this chapter, we go over the fundamental considerations in
designing and buildinga Web browser, as well as other sophisticated
Web clients. When discussing Webbrowsers, our focus will not be on
the graphical aspects of browser functionality$i.e. the layout of
pages, the rendering of images'. Instead, we shall concentrateon
the issues associated with the processing of 1TT* re#uests and
responses. Thevalue of this knowledge will become apparent as we
proceed to our discussion ofmore sophisticated Web
applications.
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JavaScript can put d)namic text into an %&' page ( A
JavaScript statement li'e this(
document)write!&*h+,& - name - &*/h+,&" can
write a variale text into an HTML page
JavaScript can react to events ( A JavaScript can e set to
execute when something
happens$ li'e when a page has finished loading or when a user
clic's on an HTML element
JavaScript can read and write %&' elements ( A JavaScript
can read and change the
content of an HTML element
JavaScript can be used to validate data ( A JavaScript can e
used to validate form
data efore it is sumitted to a server) This saves the server
from extra processing
JavaScript can be used to detect the visitor*s browser. A
JavaScript can e used to
detect the visitors rowser$ and . depending on the rowser . load
another page specifically
designed for that rowser
JavaScript can be used to create cookies. A JavaScript can e
used to store and
retrieve information on the visitors computer
The Real Na-e !s E'$%Scr!pt
!ava"cript*s official name is +($-"cript+. he standard is
developed and maintained by the ($- organisation.
($-'/0/ is the official !ava"cript standard. he standard is
based on !ava"cript #Netscape% and !"cript #$icrosoft%.
he language was invented by Brendan ich at Netscape #with
Navigator /.1%, and has appeared in all Netscape and $icrosoft
browsers since 2330.
he development of ($-'/0/ started in 2330, and the first edition
of was adopted by the ($- 4eneral -ssembly in !une
2335.
he standard was approved as an international I"O #I"O6I( 20/0/%
standard in 2337.
he development of the standard is still in progress
DYNAMIC - HTML
3ascading 5tyle 5heets $355' and =ava5cript 5tyle 5heets used
in
concert with5cripting is what puts the dynamism in Kynamic
1T
It also means thatyou can have an image that not only animates
but can move aroundthe page instead ofbeing con6ned to a stationary
rectangular space.Gou embellish your content by making stylistic
choices that aect thecolor, siHe,font face, boldness, and other
aspects of tet markup, and you cancreate margins and
http://www.ecma-international.org/publications/index.htmlhttp://www.ecma-international.org/publications/index.htmlhttp://www.ecma-international.org/publications/index.html
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borders for your tet. Then you can position your content
eactlywhere you want it toappear in the page instead of the old
inline 0ow method. Transparentand opa#ue blocksof content are now
possible which you can change, move, resiHe, makeappear or
disappear on-the-0y, or respond to user input. If so inclined,you
could let each user custom design how the website will appear
for
them.Time will de6nitely be saved if you have a particular style
that youwant to use foryour whole site or section of it by creating
the 5tyle 5heet +ust onceand saving it in its own 6le and then
accessing it multiple times withone line of code. Gou +ust !I(M to
the 5tyle 5heet when you want it toapply to that speci6c page.The
tet layout paradigm of 5tyle 5heets has been directly ported
fromthe desktoppublishing world where programs like Nuark)press
have had 5tyle5heets for years. If
you are familiar with that then youLre already halfway home
tounderstanding 3ascading5tyle 5heets in 1T
getting 1T
When you use the O5TG!4P 4lement, you have to declare with the
TG*4 2ttributewhich type of 5tyle 5heet it is, either
TG*4QRtet@355R or TG*4QRtet@=ava5criptR.9or the purposes of clarity
and brevity 'SS syntax $3ascading 5tyle 5heet synta'refers to synta
declared as8TYPE="text/CSS"
When the term3avaScr!pt syntax is used it refers to synta
declared as8TYPE="text/JavaScript"
E-Commerce
What !s e5co--erce4
4lectronic commerce or e-commerce refers to a wide range of
online businessactivitiesfor products and services.A It also
pertains to Sany form of business transaction inwhich the parties
interact electronically rather than by physical echanges or
direct
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physical contact.B
4-commerce is usually associated with buying and selling over
the Internet, orconductingany transaction involving the transfer of
ownership or rights to use goods orservices through a
computer-mediated network.Though popular, this de6nition isnot
comprehensive enough to capture recent developments in this new
andrevolutionarybusiness phenomenon. 2 more complete de6nition is8
:commerce is the
use o% electronic communications and digital in%ormation
processing technology inbusiness transactions to create' trans%orm'
and rede8ne relationships %or valuecreationbet)een or among
organi;ations' and bet)een organi;ations and individuals.F$s
ecommerce the same as ebusiness
