Notes of module 1st.....
WEB
PROGRAMMING
INTRODUCTION
AND HISTORICAL PERSPECTIVE
BASIC
CONCEPTS:-
The
Internet is a global system that consists of millions of public, private,
academic, business and government network of local to global scope.
The
Internet began in 1969, as an experimental four-computer network called ARPAnet, which was designed by U.S Defense Department so that research
scientists could communicate. In two years it grew about two dozen sites and by
1981, consists of more than 200 sites. In 1990, it was officially disbanded and
the network which now consists of hundred of sites, came to be known as Internet.
Internet
allows all the computers connected to it to exchange the information with one
another. To make communication possible, computers on the internet use a common
set of rules called protocols. The standard TCP/IP (transmission control
protocol/internet protocol) suite is used by the internet to serve millions of
users worldwide.
The
information contained within the internet can be accessed through a number of
standardized interfaces. It is believe that millions of people worldwide are
somehow connected to the WWW. The
primary way to query this giant database is the WWW. Although there are various
ways to retrieve information from the internet, WWW is mainly responsible for
tremendous growth of the internet and the people who access it.
Many
people often use the term internet and worldwide web interchangeably. However the
internet and worldwide web are not one. In fact, internet is a global data
communication system. On the other hand WWW is a repository of information
(called resources) that can be accessed via internet.
The origin of the web:-
The
worldwide web was started as the European Organization for Nuclear Research
(CERN), laboratory, Switzerland, as networked information project by an
Englishman Tim Berners-Lee in the
late 1980s. In March 1989 he wrote his first proposal entitled “a large
hypertext database with typed links”. In his proposal, he showed how information
could be transferred easily over the Internet by using hypertext. Tim’s boss Mike
Sendall encouraged him to implement his system with a work station NeXTcube,
which later became world’s first web server.
The
proposal was rewritten and published on December 1990. Lee developed all the
tools for the WWW: the Hyper Text Transfer protocol (HTTP) 0.9, Hyper Text
Markup Language (HTML), the first web browser (which was also a web editor),the
first HTTP server , the first web site http://info.cern.ch ,and a few web pages.
http://info.cern.ch/hypertext/WWW/TheProject.html was the first web page address, which primarily
focused on the WWW project itself. The first practical web browser ‘Mosaic’ was
introduced in 1993 by Marc Andreessen and it was the turning point of WWW. It became commercially during 1996-98, when a
large number of dot-com companies used it for placing their services on web.
WEB PAGE
The
information from WWW is typically accessed as ‘web pages’ or HTML documents. Web
pages contains links (called hyperlinks) , which allow us to access other web
pages by simply clicking on them.
Web
pages are viewed using software called ‘browser’. The first successful browser
was ‘mosaic’. Commonly used browsers are Google chrome, Microsoft’s Internet
Explorer, Mozilla’s Firefox etc.
WEB SITE
A website or simply site is a set of related web pages that are addressed and retrieved with a common domain name or IP
address. Websites are hosted on a
computer system known as a web server
also called HTTP server, accessible
via a network such as internet or a private local area network (LAN) through an Internet address known as a
Uniform Resource Locator (URL) .
A website can be a
personal, commercial, government or nonprofit organization website. They are
typically dedicated to a particular topic or purpose. Any website can contain a
hyperlink to any other website. Apache is the most commonly used web server
software. A website can be a dynamic or static.
WEB APPLICATION
Web applications are those applications that are accessed by the
web browsers usually through the network. Each web application is identified by
its URL. Web application run on a server is known as web server.
Types of web application
·
Service
oriented web applications- these applications implement web services and are
typically coded using server-side technologies. Such as CGI, JSP, ASP etc.
·
Presentation oriented
web application- these applications are usually clients of service oriented
applications. They are coded in browser supported languages such as HTML, XML, JAVA
Script etc. these application generates interactive web pages.
TCP/IP PROTOCOL SUITE
TCP/IP
is an acronym for Transmission control protocol/Internet Protocol. The TCP/IP
protocol suite is the set of protocols used in the internet and other
communication network. It creates the technical foundation of the Internet. It
is the collection of protocols, applications and services that helps to move
data from one layer to another layer.
The
layers of TCP/IP suite are as follow-
Application Layer
|
Transport Layer
|
Internet Layer
|
Link Layer
|
Each
layer provides well define set of services to its upper layer. Similarly each
layer uses service provided by its lower layer.
LINK LAYER
This
is the lower most layers in the TCP/IP protocol suite. It deals with Local Area
Network (LAN). It is responsible for transferring data from one machine to
another within the same local network. Following are the main functions of the
link layer-
·
Framing
·
Error
detection
·
Error
correction
·
Flow control
·
Error control
·
Medium access
control
Internet layer
The main task of this layer is to deliver data
packets from one network to another. It determine a optimal route for the
source computer to the target and delivers packet through this route. this
process is called routing. For this, it introduces an addressing mechanism call
IP addressing.
Transport layer
The task of this layer is end-to-end message
transfer. Two types of services are provided here are-
·
Connection-oriented-here
the segments of a message are deliver in order
·
Connection-less-
here no such guarantee is given.
This
layer also introduces port no to identify the process that run in a computer. Following
tasks are also implemented here-
·
segmentation
·
flow control
·
error control
·
congestion
control
Application layer
This
layer is the top most layers in the TCP/IP protocol suite. This is the layer
that uses actually interact with. It provides interfaces to users for network
communication. For example- it provides an interface using which users can
transfer file from one computer to another computer. List of some other
protocols it implements are-
·
HTTP
(Hypertext Transfer Protocol)
·
SMTP (Simple
Mail Transfer protocol)
·
DNS (Domain
Name System)
·
ASP (Active
Server Pages)
·
JSP (Java
Server Pages), etc.
URL AND ITS ANATOMY
WWW
is a repository of information called resources. URLs are used to address these
resources. It is actually case of the general addressing protocol, Uniform
Resource Identifier (URI). These are location independent addressing mechanism
used on WWW. It consists of several parts which represents specific
information. These parts are-
Protocol: //host:[port]/[path[?params][#anchor]]
·
Protocol-
it indicates the protocol used in the URL. For HTTP URL the protocol is http.
Other possible protocols are ftp,
gopher, mailto, news, nntp, telnet, wais, file and Prospero.
·
Host-
this is the Fully Qualified Domain Name (FQDN) or the IP address of the
computer where the web server runs.
·
Port-
this indicates the optional port number of process to connect. The port number
of a process is unique positive integer assign to it. If many processes are run
in a computer the port number uniquely identifies a particular process within
it. The web server typically runs on port 80.
·
Path-
It is the location in the file program in (CGI, PHP, and JSP etc) on the server
related to a document root specified by the web server.
·
Params-
This portion of the URL contains the parameter to be passed to web application
such as CGI, PHP, and JSP etc. The path and param is separated by an (?)
character.
·
Anchor-
This part indicates a specific location in web page.
Some
examples of URL are-
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