1. Surfing the Net

2. SURFING Surfing means to browse by going from place to place in search of something that interests you. On the internet, surfing means to use a program called a browser to go from site to site in search of information that interests you. The most popular place to surf on the internet is the world wide web.

3. The web is a worldwide hypertext system that interconnects millions of documents. The connections between these documents are made through links, which can be textual or graphical. A link is a hot spot which, when selected triggers the object of the link. You select the link by clicking on the word or

4. Picture that triggers it. Progressively clicking through the web by triggering the links that interest you is known as browsing, a term synonymous with surfing the net.

5. BROWSERS It is a computer program (interface) one uses to explore the world wide web. Most browsers – Respond to the following navigation buttons or keys Forward Back Restore or refresh Home – Print page – Provide a navigation line for entering a new web address – Display images

6. BROWSERS – display translated HTML documents as pages – Display the HTML codes in a document – Play video and sound clips with the help of a plug- in, an independent program module that can be added to the browser.

7. URL Uniform Resource Locator describes the location or internet address of the specific resource we want to use for our document. The home page is the first page or main page for a series of related web pages called a website. The general form of a full URL is protocol://domain name/path/filename

8. URL Protocol of a URL identifies the format of the information being accessed from the internet. Domain name specifies the physical location of the file or information resource. A domain is the computer that runs the web server software handling the protocol specified in the first part of the URL.

9. Elements of a URL A URL can have several parts, which always appear in this order: – Protocol – Server name – Port number (optional) – Filename (optional) – Anchor (optional)

10. Server name: the server name is the internet address of the computer or file server on which the resource resides Port number: port numbers rarely appear in URLs because almost every file server is on the web’s default port, which is port 80 Filename: the filename is the name the file has on the server.

11. If the files is in a folder or subfolder on the server, the filename includes the path to the file as well as the name of the file. If a URL that begins with http does not contain a filename, the default filename (usually index.html) gets served. Anchor: the anchor is a named bookmark within an HTML file. Anchors are optional.

12. If a URL does not contain an anchor, the browser begins display at the start of the file Example http://www.cug.edu.gh/homepage.html#news Protocol – http Server name – www.cug.edu.ghwww.cug.edu.gh Filename – hompage.html Anchor - news

13. PROTOCOLS USED IN URLs File: it is used to locate a file for the browser to read. Usually the file is located on the same computer as the document that points to it. It has three slashes, not two, and the drive letter “C” is followed by a vertical bar, not a colon. E.g. File:///c|foobar.htm ftp is used to bring a resource from another computer to the user’s computer. Usually ftp is used when you want your users to be able to download or copy a file to their computers. E.g. ftp://ftp.fancyfoo.stuff/foobar.txt

14. PROTOCOLS USED IN URLs Gopher: it transfers control to a gopher site and allows you to display the files available on that gopher space, also called gopher hole. E.g. gopher://deep.gopher.hole/ http is used for links that point to other web pages. mailto: it will start a mail program if the browser supports mailto URLs. Mailto is often used to request feedback about a Web page. E.g. mailto:someone@somewhere.net

15. PROTOCOLS USED IN URLs News: if the browser supports Usenet news URLs, it will open the newsreader and allow one to begin reading that newsgroup. E.g. news:alt.some.cool.newsgroup telnet: it will help login remotely with the computer specified. E.gs. telnet://user:password@server.porttelnet://user:password@server.port telnet://server:port The first one includes the username and password but the second, prompts the user for the id and password

16. 16 Uniform Resource Locators (URLs) Specifies the location of files on other servers The syntax is: scheme : // host.domain [ : port ] / path / filename

17. 17 Uniform Resource Locators (URLs) Scheme is one of : file: for a file on the local system; ftp: for a file on an anonymous FTP server; http: for a file on a WWW server; gopher: for a file on a Gopher server; telnet: a connection to a Telnet-based service,

18. 18 Uniform Resource Locators (URLs) Host domain: IP address or the logical name of the WWW server, Port number: Identifies the service (can generally be omitted) Filename: Document name

19. SURFING CONCEPTS AND TECHNIQUES Entering URLs Home pages – home page is the taking – off point. Default pages Scrolling pages - when a web page contains more information than can fit on the screen, a scroll bar will appear. A scroll bar is a control that lets one move the contents of a window up or down to reveal more information.

20. Triggering links: two kinds are hypertext and hyperpicture. Hypertext triggers consist of one or more words that one click to trigger the events that are linked to the text. They are also known as hot words because they make things happen when one click them. One can change the default color of the hot words by modifying one’s browser’s preferences

21. Hyperpicture triggers are pictorial hot spots that one clicks to trigger events linked to images on the screen. Well-designed web pages make it obvious where to click to make different things happen. Poorly designed pages can be confusing when it’s not clear what will happen when you trigger a link.

22. Navigation buttons and keys: at the top of a browser one can find a row of navigation buttons named back, forward, home, and stop, among others. One of the most useful navigation buttons is the Back button.

23. 23 Web documents Static - defined in text file by page author and remain unchanged until edited by author; Dynamic - documents are generated on demand by HTTP server; Active - the server sends a program code to be executed by the WWW browser on the client computer.

24. Web sites: every hypertext document on the world wide web resides on one of the computers connected to the network. The place where the hypertext document is stored on that computer is known as its web site. Every web site has a URL Web pages: each site on the web consists of one or more pages. Each page at a web site is known as a web page.

25. Web pages can contain more information. Scroll bars let one move the page up and down inside the browser’s winder, which displays the text and graphics on the web page.

26. 26 Web documents Document typeDescriptionAdvantages/disadvantages Static 1.Text file on server 2.Edited by author 3.Contents unchanged (until edited) 1.Easy to generate 2.Fast to display 3.Inflexible Dynamic 1.Program on server 2.Output returned to client 3.Client displays as HTML page 1.Can generate contents at time of access 2.Harder to author 3.Must be refreshed to update display Active 1.Consists of a program that is downloaded to browser 2.Browser executes program: 3.Interacts with user through keyboard 4.Updates display 5.Can read files and contact other Internet services 1.Browser must be able to run program 2.Program must be platform independent 3.Requires more complexity in browser 4.Standards not fixed (Java is de facto standard 5.Requires programming skill (typically more than dynamic)

27. 27 Static Web documents WWW document is called a Web page initial page for individual or organization is called a home page initial page can contain many different types of information and must specify: - content; - type of content; - location; - links.

28. 28 Static Web documents document can hold: text (hypertext), graphics, sound, animation, video document is composed by two parts: Head - contains details about the document; Body - contains information/content.

29. 29 Static Web documents page is represented in ASCII text with embedded HTML tags formatting instructions (for the beginning of formatting:, for the end of formatted section: ) syntax and semantic of the tags, are specified as a standard in HyperText Markup Language (HTML). the most attractive characteristic of the HTML is the possibility to integrate in one document various type of information and to generate so-called hyper-links to other documents.

30. 30 Example: Static Web documents

31. 31 activ LAN Lab - TU Sofia ACTIVITIES EDUCATION RESEARCH For additional information contact: vsfur@vmei.acad.bg BACK Static Web documents

32. 32 Client-Server interaction CLIENT SERVER Request for http://www.yahoo.com 1 4 Sending file index.htm 2 Looking for the Web page: File: Index.htm 3 Read the Web page: File: Index.htm

33. 33 Server: Must be able to execute a program under a request from the client, to generate dynamic document Returns the output of this program - a document like a static page Each dynamic document needs separate program Must differentiate between static and active document references Dynamic Web documents

34. 34 Standard defining server-client interaction is Common Gateway Interface (CGI) CGI specifies: the language of client-server interaction - (how to indicate the requested program for execution); parameter passing - the mechanism of parameter transfer from the client to the server output from CGI program is routed to WWW browser of the client Dynamic Web documents

35. 35 Can be in several formats, e.g., plain text or HTML, but must be declared explicitly: Content-type: text/html Content-type: text/plain. Client's request addresses the path for CGI-program allocation: Location: http://other.server.com/new.txt Server passes inputs to CGI programs through parameters The parameters are supplied by the client (browser) as an extension of URL with additional parameters, separated by "?". Dynamic Web documents

36. 36 Keyword of the variableMeaning SERVER_NAMEThe domain name of the computer running the server. GATEWAY_INTERFACEThe version of the CGI software the server is using. SCRIPT_NAMEThe path in the URL after the server name. QUERY_STRINGInformation following "?" in the URL REMOTE_ADDRESS The IP address of the computer running the browser that send the request. CGI parameters

37. 37 Client-Server interaction

38. 38 consist of code executed on computer running browser (Client) instead of transfer of results of a server program, the server sends the program in a specific form the results are obtained in the client side displayed on its computer the network traffic is highly decreased as well as the server congestion Active Web documents

39. 39 Client-Server interaction