Www and internet
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WWW and Internet. The Internet Creation of the Web Languages for document description Active web pages. Internet. ARPANET – 1970s. Protocols TCP/IP: Transmission Control Program/Internet Protocol - low level Telnet SMTP - Simple Mail Transport Protocol FTP - File Transfer Protocol.

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Www and internet

WWW and Internet

  • The Internet

  • Creation of the Web

  • Languages for document description

  • Active web pages


Internet

Internet

  • ARPANET – 1970s.

  • Protocols

    • TCP/IP: Transmission Control Program/Internet Protocol - low level

    • Telnet

    • SMTP - Simple Mail Transport Protocol

    • FTP - File Transfer Protocol


Creation of the web

Creation of the Web

WWW provides a semantic description of the information accessible through the Internet.

Server program: to provide the document

Client program: to read and display the document.

Server and client communicate via

HTTP - HyperText Transport Protocol.


Basic idea

Basic Idea

WWW is based on the concept of a semantic description language.

The power of the system is that the displayed document contains pointers to other documents called hypertext.


Url uniform resource locator

URL: Uniform Resource Locator

Client program:

uses URLs to locate documents and display in the web browser

A database of addresses and names is maintained by a Domain Name Server.


Other programs

Other programs

Search engines – allow user to query site for desired information

Web crawlers – crawler trace all links on a Web page to find other Web pages


Www and internet

WEB NAVIGATION


Languages for document description

Languages for documentdescription

SGML: Standard Generalized Markup Language

HTML – HyperText Markup Language

XML – Extensible Markup Language


Www and internet

SGML

SGML uses descriptive tags.

DTD –document type declaration, describes the elements

What is described:

-      Document presentation (e.g. boldface, italics)

-      Document structure (text split into divisions, chapters, paragraphs, etc)

-      Document history (author, revisions, etc)


Www and internet

HTML

  • HTML creates a virtual machine that web browsers are programmed to execute.

  • Important elements-

  • Sections – Separate parts of a document

  • Presentation – How documents look.

  • List – Lists of items

  • URLs – links to other web pages

  • Image URLs – displays pictures


Www and internet

XML

An instance of SGML.

Incorporates many features of HTML.

Uses DTD to describe the semantics of the document.


Active web pages

Active web pages

  • Forms and CGI scripts

  • Java Applets


Forms and cgi scripts

Forms and CGI scripts

  • Forms – Method to pass information between Web browsers and Web servers.

  • Information is entered by the user and then passed for processing to a program on the server system

  • CGI (Common Gateway Interface) scripts - programs that process the information


Html forms

HTML forms

<form method=“type”

action= “location of cgi script to execute”>

text

</form>

Perl is often used as language for such scripts


Java applets

Java Applets

Issue: Overloaded server

Solution: Do more processing on client side of web

JAVA APPLETS


Java applets1

Java applets

  • Run on the client machine

  • Java programs compiled into a machine independent code –

    bytecode for JavaVirtual machine.

  • Browsers on local systems have Java Virtual machine interpreter


Java applet example

Java Applet Example

import java.awt.*; /* applet library */

public class hello extends java.applet.Applet

public void paint(Graphics x)

{x.drawString(“Hello World”, 100, 100);}

Displayed by:

<html><body>

<applet code = “hello.class” width=200 height=200>

</applet>

</body></html>


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