Postacademic Interuniversity Course in Information Technology – Module C1p1 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images

Postacademic Interuniversity Course in Information Technology – Module C1p2 World Wide Web 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.

Postacademic Interuniversity Course in Information Technology – Module C1p3 WWW page example

Postacademic Interuniversity Course in Information Technology – Module C1p4 Search Engines 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

Postacademic Interuniversity Course in Information Technology – Module C1p5 Technically, what is it ? 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 The WEB = Internet + HTML + URL + HTTP

Postacademic Interuniversity Course in Information Technology – Module C1p6 Technically, what is it ? 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 The WEB = Internet + HTML + URL + HTTP

Postacademic Interuniversity Course in Information Technology – Module C1p7 HTML HyperText Markup Language 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

Postacademic Interuniversity Course in Information Technology – Module C1p8 HTML HyperText Markup Language 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)

Postacademic Interuniversity Course in Information Technology – Module C1p9 HTML HyperText Markup Language 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)

Postacademic Interuniversity Course in Information Technology – Module C1p10 Technically, what is it ? 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 The WEB = Internet + HTML + URL + HTTP

Postacademic Interuniversity Course in Information Technology – Module C1p11 URL Universal Resource Locator Protocol used to communicate with resource (each protocol further defines URL format) Internet Resource Address –Domain name Internet Protocol address of machine ( ) 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) http: 80 //

Postacademic Interuniversity Course in Information Technology – Module C1p12 Technically, what is it ? 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 The WEB = Internet + HTML + URL + HTTP

Postacademic Interuniversity Course in Information Technology – Module C1p13 HTTP 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.

Postacademic Interuniversity Course in Information Technology – Module C1p14 Inside the Web HTTP Client (Web Browser) HTTP Server Other ServerHTTP Server HTTP Link transporting HTML- encoded hypertext Other Data Link

Postacademic Interuniversity Course in Information Technology – Module C1p15 HTTP Hypertext Transfer Protocol Stateless (connectionless) communication protocol Uses a connection oriented transport protocol. Typical HTTP 1.0 transaction: 1Client HTTP entity opens transport connection with specified Server HTTP entity. 2Client makes the request to the server. 3Server sends response. 4Server 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.

Postacademic Interuniversity Course in Information Technology – Module C1p16 HTTP Network Service Transport entity Transport entity Connection oriented protocol Server HTTP Connectionless protocol Client HTTP Browser Web Server

Postacademic Interuniversity Course in Information Technology – Module C1p17 HTTP is a Stateless Protocol Benefit : performance of server Penalty : Server can not keep information about user. > 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 <.... Server HTTP Connectionless protocol Client HTTP Browser Web Server

Postacademic Interuniversity Course in Information Technology – Module C1p18 HTTP Adding state to a Stateless Protocol The state is kept in the messages traveling between server and browser !!! Server HTTP Connectionless protocol Client HTTP Browser Web Server > 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 <