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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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Presentation Transcript
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

languages for document description
Languages for documentdescription

SGML: Standard Generalized Markup Language

HTML – HyperText Markup Language

XML – Extensible Markup Language

slide9
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)

slide10
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
slide11
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

action= “location of cgi script to execute”>

text

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);}

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