World-Wide Web

Institute for Visualization and Perception ResearchI VPR 1

© Copyright 1998 Haim Levkowitz

World-Wide Web

• Introduction to the World-Wide Web• Setting up a Web server• Authoring for the Web ...• Gateways and forms• Access control and security



History ...• CERN, Geneva, 1989• Def HTTP client/server protocol• Sample server• Prog. lib. wwwlib

• 1992: callable interface in public domain• ==> Development

• Web browsers• New features

• Now browsers & servers for all major architectures



Original goals

• Link distinct documents • Success

• Facilitate collaborative authoring• Not so much, yet



Introduction to the World-Wide Web• Components of Web architecture ...• What's the Web good for? ...• Basic Web Concepts ...• WWW Servers and Browsers ...• Searching on the Web …



Components of Web architecture …• HTML: Hyper Text Markup Language• HTTP: Hyper Text Transfer Protocol• CGI: Common Gateway Interface

Web clients

Web servers

Databases

Contents

Software applications

CGITCP/IP-based

network



Powerful linking abilities ...• Highlight words/pictures

• ==> Link/point to other• Documents• Sound files• Movie clips

• From any point to any point



Most graphical Internet service ...• Need browser w/GUI• Click on link to follow



What's the Web good for? ...• Museums• Newspapers, magazines• Business• Investment information• Libraries, universities• Governments• Individuals



Basic Web Concepts ...

• Hyperlinking ...• The HTML Tagging Language ...• The URL Concept ...• What's a WWW Browser? ...• What's a WWW Server? ...• HTTP ...



Hyperlinking ...

• Home page: central doc. in Web server• Hyperlinks (underlined)

• Navigate: follow hyperlinks (surfing)• Anywhere on Web servers in the

world! ...



Anywhere on Web servers in the world! ...

• -

10

Server 1 (DEC) A

B

Server 2 (Suny-Buffalo)

CServer 3 (GNN) D

E

Server 4 (Exploratorium)

F



The HTML Tagging Language ...• Hypertext Markup Language• HTML Documents• Describe structure of doc &

hyperlinking info• No exact formatting

• Example ...



Example ...

• . <H1>NCSA Mosaic Demo Document</H1> Welcome to NCSA Mosaic, an information browser developed at the National Center for Supercomputing Applications at the University of Illinois, Urbana-Champaign. <P> This document is an interactive hypermedia tour of Mosaic's capabilities. <H2>Introduction</H2> <UL> <LI> Mosaic is an Internet-based <EM>global hypermedia</EM> browser that allows .... <LI>Mosaic is part of the World Wide Web project ... </UL>

Header

Parag.

Bulleted list



The URL Concept ...

• Each hyperlink, 2 components:• Anchor text/graphics

• Trigger hyperlink when clicked• Universal Resource Locator (URL) ...



Universal Resource Locator (URL) ...• What to do when HL activated• Protocol to reach

• Target server• Host system (server name) where doc is• Directory path• Filename

• E.g., master list of all public WWW server in world• http://info.cern.ch/hypertext/DataSources/WWW/

Geographical.html (absolute)



What's a WWW Browser? ...• Client/server environment• Browser

• Use URL• Retrieve Web document from Web server• Interpret HTML• Present document to user

• Bitmap graphics ==> more than char. based• E.g., hyperlink: color/underline vs. reverse video

• Example ...



Example ...

• Protocol depends on server • Some browsers can access WAIS servers• Can start up telnet sessions

• Can save, email, print, search, see HTML source

Web BrowserWeb Browser

Gopher Server

Web Server

FTP Server

Gateway Other Servers

Gopher

HTTP

ftp



What's a WWW Server? ...

• SW used with WWW• Client asks for page; server grabs &

returns• Special scripts

• Gateways to other info resources• E.g., input from forms

• Custom scripts to process



HTTP ...• HyperText Transfer Protocol• Request browser --> server ==> new connection

• Open connection• Transfer document• Close connection

• Data types between server and browser• Text (text/html, text/plain, ...)• Image (image/gif, image/tiff, ...)

• E.g., start xv to display (Preferences: Helper App's)



WWW Servers and Browsers ...• Browsers ...• Servers ...



Browsers ...

• Netscape Navigator/Communicator• Internet Explorer• Mosaic (historic importance)• Lynx (dumb terminal)• Amaya (free)

• Browser/editor (http://www.w3.org/Amaya)• Opera (not free)



Mosaic ...

• The first publicly available browser• Made it happen!



Netscape Navigator ...

• Netscape Communications Corp. (former Mosaic Comm.)



Lynx ...• Full-screen, character-based

• VT100 terms, emulators• Arrow keys to navigate among HTML links (reverse

video)• Bookmarks• Forms• Interactive mode: post articles to newsgroups• Non-interactive mode: filter HTML to formatted ASCII• ftp://ftp2.cc.ukans.edu/pub/lynx/



Many others

• Came and went• Maybe 10% of today’s users



Servers ...

• NCSA• CERN• Apache (48% of all servers)• Netscape Enterprise• O’Reilly’s WebStar• Other



NCSA ...• Public domain, written in C, small, fast• No licensing restrictions• Compatible with most HTTP browsers• Directory aliasing: doc's can be served from any

physical directory structure• Searches, HTML forms, clickable image maps,

control user access.• http://hoohoo.ncsa.uiuc.edu/docs/setup/

PreCompiled.html



CERN ...• Public domain, written in C• No licensing restrictions• Compatible with most HTTP browsers• Directory aliasing: doc's can be served from any

physical directory structure• Searches, clickable image maps, control user access• Proxy & caching

• On firewall machines access to outside world from inside



Work in progress ...

• See http://www.w3.org• User Interface• Technology & Society• Architecture• Web Accessibility Initiative• Other



User Interface• HTML Enhancements

• http://www.w3.org/MarkUp.html• Style Sheets• Document Object Model• Mathematics• Graphics• Internationalization• Fonts• Amaya



Technology & Society

• Digital Signature Initiative• Metadata• PICS• Privacy• Security• Electronic Commerce



Architecture

• HTTP• Synchronized Multimedia• XML• Jigsaw• Libwww



Web Accessibility Initiative

• Accessibility of the Web• Through five primary areas of work:

• Technology• Guidelines• Tools• Education & outreach• Research & development



Secure Transactions ...• Credit card numbers• Signatures (electronic)• Legally binding time stamps• Secure HTTP development

• Authority of transactions• Confidentiality of info exchanged• http://www.commerce.net/information/standards/

drafts/shttp.txt• email: [email protected]



Uniform Naming ...

• URL: no uniquely identify doc• Only instance of doc• No account for mirrored doc's, versions out of date

• URN: Universal Resource Name • Unique doc identifier

• Like ISBN for books• Return URL of closest copy?

• URC: Universal Resource Citation (just a diff name)



Commercialization ...

• Bundle browser w/systems• License browsers + sell• ==> Web onto more desktops• Info providers + publishers• Secure web ==> electronic commerce



Searching on the Web ...

• Catalogs, directories• Manual• E.g., Yahoo

• Indices, search engines• Automatic • E.g., AltaVista



Search Engines ...

• "Robots," "worms," "spiders," "crawlers,” meta searchers

• No ultimate search tool on the Web• Different search strategies

• ==> Different results• Partial list ...• More info ...



Partial list ...

• Metacrawler ...• Alta Vista ...• WebCrawler ...• Lycos• InfoSeek• Copernic



Comparison ...

• IEEE Internet Computing, July/August 1998, pp. 78-83, http://computer.org/internet/v2n4/w4arach.htm

• http://www.cnet.com/Contents/Reviews/Compare/Search/ (old)



More info ...• "New Spiders Roam the Web"

• http://www.rpi.edu/~decemj/cmc/mag/1994/sep/spiders.html

• "WWW Robots, Wanderers, and Spiders"• http://web.nexor.co.uk/mak/doc/robots/robots.html

• Netscape Web page• http://home.mcom.com/home/internet-search.html• Click Net Search button in Netscape



Internet Research Tool Kit

• Links to most search & research tools• http://www.cs.uml.edu/~haim/

NetResearch_links.html

World-Wide Web

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