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World-Wide Web = WWW

World-Wide Web = WWW. Introduction. The World-Wide Web: summary. The following gives an overview of the World-Wide Web: Description / definition of the WWW and its relation with the Internet Client programs that allow you to use the WWW

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World-Wide Web = WWW

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  1. World-Wide Web = WWW Introduction

  2. The World-Wide Web:summary The following gives an overview of the World-Wide Web: • Description / definition of the WWW and its relation with the Internet • Client programs that allow you to use the WWW • How to save selected information from the WWW to your computer? • The success of the WWW

  3. The World-Wide Web:prerequisites Before using the WWW you should ideally already have learned to understand and to use • computer hardware • computer software • the Internet • older methods for online communication, such as telnet

  4. Example The WWW: example of a welcome page

  5. !? Question !? Task !? Problem !? Indicate some difference between the older telnet and the newer World-Wide Web?

  6. The WWW: views on information space • Unlike telnet and ftp, the WWW offers a view on one virtually unified but decentralized information space. • Selecting a server, and switching from one server to another is easier than with telnet and ftp. • A client program for the WWW can be used to search for information held on a distributed network of WWW hosts / servers. • A WWW client has a seamless view of the information, even though this information is distributed over many different hosts.

  7. URL = Universal Resource Locator • = standard for specifying an object on the Internet • the structure is in most casesprotocol://computer_address[/path_name/file_name] • examples: • telnet://biblio.vub.ac.be • ftp://ftp.vub.ac.be/ • gopher://gopher.vub.ac.be/ • http://www.vub.ac.be/BIBLIO/index.html • news://news.server.edu/comp.infosystems.www

  8. URLformat / structure 1. The first part of a URL, before the colon “:”, specifies the access method = protocol 2. The second part of the URL, after the colon “:”, is interpreted specific to the access method. In general, two slashes after the colon indicate a machine /computer name.

  9. WWW = World Wide Web = W3: description • The WWW provides a hypertext-hypermedia interface to information resources in the Internet.So WWW is a distributed hypermedia system. • The basis of the WWW was developed at CERN (the European Laboratory for Particle Physics) in Switzerland by Tim Berners-Lee and co-workers.

  10. !? Question !? Task !? Problem !? What is the difference between Internet and the World-Wide Web?

  11. The WWW is an application of Internet • The World-Wide Web (WWW) is a service, an application of Internet. • It is based on the Internet infrastructure. • So the WWW is newer than the Internet. The concept of the WWW was created at the end of the 1980s when the Internet was already well established.

  12. The WWW is an application of Internet: scheme Data communication Internet WWW

  13. The WWW: the essential elements • Information delivery and access using hypertext/hypermedia documents/objects • html documents • http protocol: http clients http servers • Integration of protocols in the Internet: • http servers offering html documents including links to other http servers, telnet servers, ftp servers, nntp servers, gopher servers, ,...

  14. The WWW: function • The WWW works by establishing hypertext/hypermedia links between documents anywhere on the network. • A document might include many links to other documents held on many different servers. • Selecting any one of those links will take you to the related document wherever it is. e.g. the references at the end of a paper might have hypertext links to the actual documents held elsewhere.

  15. The WWW: hyperlinks Hyperlinks can link a part of a hypermedia document to • another part of the same document file • another document file on the same server computer • another document file on a server computer located elsewhere in the world Computer 1 Computer 2

  16. The WWW: hypertext mark-up language = HTML • Hypertext mark-up language = HTML = the system of codes used by authors to build the hypertext-pages/files in WWW, for instance to create a title or an anchor. • The codes are invisible / transparent for the user / reader.

  17. The WWW: hypertext transfer protocol = HTTP • Hypertext transfer protocol = HTTP = the software conventions used by client and server programs for WWW to request and transfer hypermedia documents. • The protocol must not be known by he user / reader = the protocol is invisible / transparent for the user. • Analogous with the telnet, ftp and gopher protocol.

  18. !? Question !? Task !? Problem !? Briefly compare TCP/IP and HTTP.

  19. The WWW: pages and forms • Pages Many documents developed for WWW are kept small and are named “pages”. These often refer to several other “pages”. • Forms = gateways to services and databases on server computers in WWW Some pages contain electronic forms, to be filled in by the user.

  20. The WWWapplications Analogous to gopher applications: • Access to online public access catalogues • Campus-wide information systems • Access to subject-oriented information • Access to computer file archives • Traveling / navigating through the Internet via linked html-pages • Access to intranets within institutes / companies

  21. World-Wide Web = WWW WWW client programs

  22. WWW: client / browse programs • To access the WWW, you run a browser program. • The browser reads documents, and can fetch documents from other sources. Information providers set up hypermedia servers which browsers can get documents from. • The browser can display hypertext documents. Hypertext is text with pointers to other text. The browsers let you deal with the pointers in a transparent way: select the pointer, and you are presented with the text that is pointed to.

  23. WWW: browsers for your own computer • The preferred method of access of the Web is to run a browser yourself on your computer. • These provide not only an interface to http-servers in WWW, but also to various other protocols • ftp • gopher • SMTP, POP, IMAP (for e-mail) • NNTP (for Usenet News) • ...

  24. WWW: examples of browsers for your own computer Browsers are available for many computer platforms; in particular: browsers for Windows + Winsock: • Netscape • Microsoft Internet Explorer • ...

  25. Example Netscapefor Windows 95: screen shot

  26. Example MS Internet Explorer 4 for Windows 95: screen shot

  27. !? Question !? Task !? Problem !? Which client program do YOU use or will YOU useto access the WWW?

  28. !? Question !? Task !? Problem !? Browse the WWW, using an available browser client program.

  29. !? Question !? Task !? Problem !? Visualise the HTML source code of a WWW page, using a WWW client program. What do you learn from this exercise about the basic properties of HTML?

  30. !? Question !? Task !? Problem !? Exploit the possibility to open more than one window, using a WWW client program in Windows.

  31. !? Question !? Task !? Problem !? Why would you want to open more than one window on WWW servers,using a WWW client program?

  32. !? Question !? Task !? Problem !? What is HTTP and HTML? Explain the difference and the relation between both.

  33. !? Question !? Task !? Problem !? Is a WWW browser a client or a server?

  34. Programs to access the Web and other Internet services • The WWW has become a tremendous success in the 1990s. • It has made the Internet popular. • The programs to access the WWW have incorporated many functions to exploit other services offered by the Internet. • A consequence is that for many users the distinction between Internet and WWW is blurred.

  35. !? Question !? Task !? Problem !? What came first: Internet or WWW?Explain.

  36. World-Wide Web = WWW Saving information from a web

  37. WWW: How to save information from a web? Information displayed by your web browser/client program can be saved, • by select, copy, paste in another document (and save) • by saving a complete page to your disk • in separate files (for instance 1 HTML file + some image files) • in 1 file, using Microsoft Internet Explorer 5 or later version • by copying the information into an e-mail message that you send to your own e-mail account

  38. !? Question !? Task !? Problem !? Copy some text fragment from WWWand paste it into another document on your computer.

  39. !? Question !? Task !? Problem !? Save a text from WWW to disk, as HTML, using a browser program.

  40. !? Question !? Task !? Problem !? Display an HTML file that you have saved from the WWW to your disk,in a program for word processing. Is the file displayed properly?

  41. !? Question !? Task !? Problem !? Check if the program that you use can copy a picture from WWW, so that you can directly paste it into a document in another program on your PC.

  42. !? Question !? Task !? Problem !? Save a picture from WWW to disk, using a browser program.

  43. !? Question !? Task !? Problem !? Check if the program that you use for word processing allows you to insert a picture that you saved to diskinto your word processing document.

  44. !? Question !? Task !? Problem !? Save a document that includes at least 1 image from WWW to your disk, and test if the images are saved too, by loading the saved HTML file in a program that can show HTML files.

  45. !? Question !? Task !? Problem !? Choose a web page with images. Save this as HTML. Look at the files on your disk, that were saved there. How many and which kind of files do you observe?

  46. World-Wide Web = WWW The success of WWW

  47. WWW: growing number of WWW servers

  48. WWW as popular method to access information from computers • The WWW has quickly become the most popular medium to access information that resides on various computers that are connected to a computer network.

  49. !? Question !? Task !? Problem !? Which positive properties have made WWW so popular so fast?

  50. WWW properties leading to its success, related to access (Part 1) • The client-server architecture that is used in the web allows the user to choose a browser client program. • Browser client programs are available free of charge. • The WWW is accessible from computers with most operating systems. • The WWW offers an easy to use interface to various complex services, based on hypertext/hypermedia. • The multimedia contents are attractive.

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