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"The World Wide Web offers a user-friendly interface for accessing distributed databases. With inexpensive and high-quality browsers available for almost all computers, users can access over 500,000,000 pages worldwide. The Web also allows for sophisticated interactivity through downloading programs to be executed on the client's workstation. However, electronic commerce is still restrained by security concerns."

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  1. Data Communications Applications File & print serving Mail Domain Name Server Telnet File Transfer Protocol World Wide Web Multi-media Applications Voice Images Contents

  2. Uniform hypertext based, user friendly interface for distributed databases. Inexpensive, high quality, browsers available for almost all computers. Sophisticated and application specific user’s interactivity by downloading programs to be executed on client’s workstation (Java applets). Already over 500,000,000 pages available worldwide, mainly for public relations, publicity and, to some extent, electronic commerce. Electronic commerce still restrained by security concerns. World Wide Web

  3. WWW page example

  4. Finding information becomes more and more difficult due to the amount of information. Automated indexing services, searching all available databases on the Internet and setting up keyword databases are very popular. Good ranking of keywords can be purchased from indexing services. Many sites use tricks to be favorably presented by search engines Search Engines

  5. HTML :hypertext Markup Language. Hypertext = multimedia information(containing even executable programs) with references to other pieces of hypertexts. URL :Universal Resource Locator. The address where a piece of hypertext (or other resources) can be obtained HTTP : Hypertext Transfer Protocol. - Conventions to transfer hypertexts between computers Technically, what is it ? The WEB = Internet + HTML + URL + HTTP

  6. HTML :hypertext Markup Language. Hypertext = multimedia information(containing even executable programs) with references to other pieces of hypertexts. URL : Universal Resource Locator. The address where a piece of hypertext (or other resources) can be obtained HTTP : Hypertext Transfer Protocol. - Conventions to transfer hypertexts between computers Technically, what is it ? The WEB = Internet + HTML + URL + HTTP

  7. Hypertext Multimedia document Normal text Graphics and images (stored in separate files) Sound (stored in separate files) Executable programs ( = applets in Java code) References to other hypertext documents(“Anchors”) “clickable” normal text or image (icon) address (URL) where the corresponding document can be found HTMLHyperText Markup Language

  8. Physical Markup (used for textprocessors, not in “pure” HTML) Functional role of contents is not mentioned Describes how the document should look “new page”; “use font ‘Times-Roman 24’ “ “Print ‘Teleprocessing’ page-centered” Presentation imposed by author of document What You See Is What You Get (WYSIWYG) HTMLHyperTextMarkup Language

  9. Semantic Markup (used in original HTML) Functional role of contents is described “Main Title ‘Teleprocessing’ “ Presentation defined by interpreter settings Text only / graphics , Black & white / color,... Braille. What You Get Is What You Meant(WYGIWYM) HTMLHyperText Markup Language

  10. HTML : hypertext Markup Language. Hypertext = multimedia information(containing even executable programs) with references to other pieces of hypertexts. URL :Universal Resource Locator. The address where a piece of hypertext (or other resources) can be obtained HTTP : Hypertext Transfer Protocol. - Conventions to transfer hypertexts between computers Technically, what is it ? The WEB = Internet + HTML + URL + HTTP

  11. Protocol used to communicate with resource (each protocol further defines URL format) Internet Resource Address Domain name Internet Protocol address of machine (134.121.023.001) Domain Server Name of machine (infoweb.vub.ac.be) Port number on machine Optional : Each protocol has a default port number Resource details (protocol specific) (i.e. directory and filename of an HTML page) URLUniversal Resource Locator http: //www.info.vub.ac.be:80 /webpages/info.html

  12. HTML : hypertext Markup Language. Hypertext = multimedia information(containing even executable programs) with references to other pieces of hypertexts. URL : Universal Resource Locator. The address where a piece of hypertext (or other resources) can be obtained HTTP : Hypertext Transfer Protocol. - Conventions to transfer hypertexts between computers Technically, what is it ? The WEB = Internet + HTML + URL + HTTP

  13. HTTP : HyperText Transfer Protocol. HTTP Client : a Web Browser Presenting information encoded in HTML. Translating user interactions into the HTTP. HTTP Server : a process interpreting client requests Sending pieces of hypertext stored in HTML Translating information available in other formats acquiring information from outside the Web. HTTP

  14. Inside the Web HTTP Server HTTP Server HTTP Client (Web Browser) HTTP Server HTTP Link transporting HTML- encoded hypertext Other Data Link HTTP Server Other Server

  15. Stateless (connectionless) communication protocol Uses a connection oriented transport protocol. Typical HTTP 1.0 transaction: Client HTTP entity opens transport connection with specified Server HTTP entity. Client makes the request to the server. Server sends response. Server closes transport connection. Some HTTP implementations allow looping through steps 2 and 3 (Keep-alive) to transfer entire hypertext pages with images and sound in one HTTP transaction. HTTPHypertext Transfer Protocol

  16. Web Server Browser Connectionless protocol Server HTTP Client HTTP HTTP Connection oriented protocol Transport entity Transport entity Network Service

  17. Benefit : performance of server Penalty : Server can not keep information about user. Browser Client HTTP HTTPis a Stateless Protocol > show me my bank transactions Give your name and password < > XYZ, ****** OK, what do you want < > show me my bank transactions Give your name and password < .... Web Server Server HTTP Connectionless protocol

  18. The state is kept in the messages traveling between server and browser !!! Browser Client HTTP HTTPAdding state to a Stateless Protocol > I want to log into the server Give your name and password < > XYZ, ****** OK, here is your key 478 < > show me my bank records, my key is 478. Here are your bank records < $$$$$$$$$ < If you need more use key 953 < Web Server Server HTTP Connectionless protocol

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