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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 - PowerPoint PPT Presentation
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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
Institute for Visualization and Perception ResearchI VPR 2
© Copyright 1998 Haim Levkowitz
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
Institute for Visualization and Perception ResearchI VPR 3
© Copyright 1998 Haim Levkowitz
Original goals
• Link distinct documents • Success
• Facilitate collaborative authoring• Not so much, yet
Institute for Visualization and Perception ResearchI VPR 4
© Copyright 1998 Haim Levkowitz
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 …
Institute for Visualization and Perception ResearchI VPR 5
© Copyright 1998 Haim Levkowitz
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
Institute for Visualization and Perception ResearchI VPR 6
© Copyright 1998 Haim Levkowitz
Powerful linking abilities ...• Highlight words/pictures
• ==> Link/point to other• Documents• Sound files• Movie clips
• From any point to any point
Institute for Visualization and Perception ResearchI VPR 7
© Copyright 1998 Haim Levkowitz
Most graphical Internet service ...• Need browser w/GUI• Click on link to follow
Institute for Visualization and Perception ResearchI VPR 8
© Copyright 1998 Haim Levkowitz
What's the Web good for? ...• Museums• Newspapers, magazines• Business• Investment information• Libraries, universities• Governments• Individuals
Institute for Visualization and Perception ResearchI VPR 9
© Copyright 1998 Haim Levkowitz
Basic Web Concepts ...
• Hyperlinking ...• The HTML Tagging Language ...• The URL Concept ...• What's a WWW Browser? ...• What's a WWW Server? ...• HTTP ...
Institute for Visualization and Perception ResearchI VPR 10
© Copyright 1998 Haim Levkowitz
Hyperlinking ...
• Home page: central doc. in Web server• Hyperlinks (underlined)
• Navigate: follow hyperlinks (surfing)• Anywhere on Web servers in the
world! ...
Institute for Visualization and Perception ResearchI VPR 11
© Copyright 1998 Haim Levkowitz
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
Institute for Visualization and Perception ResearchI VPR 12
© Copyright 1998 Haim Levkowitz
The HTML Tagging Language ...• Hypertext Markup Language• HTML Documents• Describe structure of doc &
hyperlinking info• No exact formatting
• Example ...
Institute for Visualization and Perception ResearchI VPR 13
© Copyright 1998 Haim Levkowitz
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
Institute for Visualization and Perception ResearchI VPR 14
© Copyright 1998 Haim Levkowitz
The URL Concept ...
• Each hyperlink, 2 components:• Anchor text/graphics
• Trigger hyperlink when clicked• Universal Resource Locator (URL) ...
Institute for Visualization and Perception ResearchI VPR 15
© Copyright 1998 Haim Levkowitz
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)
Institute for Visualization and Perception ResearchI VPR 16
© Copyright 1998 Haim Levkowitz
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 ...
Institute for Visualization and Perception ResearchI VPR 17
© Copyright 1998 Haim Levkowitz
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
Institute for Visualization and Perception ResearchI VPR 18
© Copyright 1998 Haim Levkowitz
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
Institute for Visualization and Perception ResearchI VPR 19
© Copyright 1998 Haim Levkowitz
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)
Institute for Visualization and Perception ResearchI VPR 20
© Copyright 1998 Haim Levkowitz
WWW Servers and Browsers ...• Browsers ...• Servers ...
Institute for Visualization and Perception ResearchI VPR 21
© Copyright 1998 Haim Levkowitz
Browsers ...
• Netscape Navigator/Communicator• Internet Explorer• Mosaic (historic importance)• Lynx (dumb terminal)• Amaya (free)
• Browser/editor (http://www.w3.org/Amaya)• Opera (not free)
Institute for Visualization and Perception ResearchI VPR 22
© Copyright 1998 Haim Levkowitz
Mosaic ...
• The first publicly available browser• Made it happen!
Institute for Visualization and Perception ResearchI VPR 23
© Copyright 1998 Haim Levkowitz
Netscape Navigator ...
• Netscape Communications Corp. (former Mosaic Comm.)
Institute for Visualization and Perception ResearchI VPR 24
© Copyright 1998 Haim Levkowitz
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/
Institute for Visualization and Perception ResearchI VPR 25
© Copyright 1998 Haim Levkowitz
Many others
• Came and went• Maybe 10% of today’s users
Institute for Visualization and Perception ResearchI VPR 26
© Copyright 1998 Haim Levkowitz
Servers ...
• NCSA• CERN• Apache (48% of all servers)• Netscape Enterprise• O’Reilly’s WebStar• Other
Institute for Visualization and Perception ResearchI VPR 27
© Copyright 1998 Haim Levkowitz
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
Institute for Visualization and Perception ResearchI VPR 28
© Copyright 1998 Haim Levkowitz
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
Institute for Visualization and Perception ResearchI VPR 29
© Copyright 1998 Haim Levkowitz
Work in progress ...
• See http://www.w3.org• User Interface• Technology & Society• Architecture• Web Accessibility Initiative• Other
Institute for Visualization and Perception ResearchI VPR 30
© Copyright 1998 Haim Levkowitz
User Interface• HTML Enhancements
• http://www.w3.org/MarkUp.html• Style Sheets• Document Object Model• Mathematics• Graphics• Internationalization• Fonts• Amaya
Institute for Visualization and Perception ResearchI VPR 31
© Copyright 1998 Haim Levkowitz
Technology & Society
• Digital Signature Initiative• Metadata• PICS• Privacy• Security• Electronic Commerce
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© Copyright 1998 Haim Levkowitz
Architecture
• HTTP• Synchronized Multimedia• XML• Jigsaw• Libwww
Institute for Visualization and Perception ResearchI VPR 33
© Copyright 1998 Haim Levkowitz
Web Accessibility Initiative
• Accessibility of the Web• Through five primary areas of work:
• Technology• Guidelines• Tools• Education & outreach• Research & development
Institute for Visualization and Perception ResearchI VPR 34
© Copyright 1998 Haim Levkowitz
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]
Institute for Visualization and Perception ResearchI VPR 35
© Copyright 1998 Haim Levkowitz
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)
Institute for Visualization and Perception ResearchI VPR 36
© Copyright 1998 Haim Levkowitz
Commercialization ...
• Bundle browser w/systems• License browsers + sell• ==> Web onto more desktops• Info providers + publishers• Secure web ==> electronic commerce
Institute for Visualization and Perception ResearchI VPR 37
© Copyright 1998 Haim Levkowitz
Searching on the Web ...
• Catalogs, directories• Manual• E.g., Yahoo
• Indices, search engines• Automatic • E.g., AltaVista
Institute for Visualization and Perception ResearchI VPR 38
© Copyright 1998 Haim Levkowitz
Search Engines ...
• "Robots," "worms," "spiders," "crawlers,” meta searchers
• No ultimate search tool on the Web• Different search strategies
• ==> Different results• Partial list ...• More info ...
Institute for Visualization and Perception ResearchI VPR 39
© Copyright 1998 Haim Levkowitz
Partial list ...
• Metacrawler ...• Alta Vista ...• WebCrawler ...• Lycos• InfoSeek• Copernic
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© Copyright 1998 Haim Levkowitz
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)
Institute for Visualization and Perception ResearchI VPR 41
© Copyright 1998 Haim Levkowitz
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
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© Copyright 1998 Haim Levkowitz
Internet Research Tool Kit
• Links to most search & research tools• http://www.cs.uml.edu/~haim/
NetResearch_links.html