About the World Wide Web
[Pages and HTML] [Clients and Servers] [Hyperlinks] [URL] [IP number]

The World Wide Web is a graphical Internet service that provides a network of interactive documents and software to access them. It is based on documents called pages that combine text, pictures, forms, sound, animation and hypertext links called hyperlinks. To navigate the World Wide Web, users "surf" from one page to another by pointing and clicking on hyperlinks in text or graphics.

 

Pages and HTML
The basic document of the World Wide Web is a page. Pages are written in an evolving language called HTML (HyperText Markup Language). An HTML page contains text along with tags, embedded commands that supply information about the page's structure, appearance and contents.

Some HTML tags build structural descriptions of page items, such as tables and forms, which are made up of many elements. Browsers (=programs that display pages) use this information to determine how to display the page elements in relation to each other. For example, the HTML tag that describes a table, specifies the number of rows it has, the number of cells in a row and so forth.

Along with describing the structural relationships among page elements, some HTML tags also contain attributes. Attributes provide details about a particular tag. For instance, the tag that inserts an image on a page has an attribute that supplies the name of the image to insert. Some attributes supply preferences about the layout of the page element. For example, a table has attributes that describe its border width and the padding between its cells.

 

Web browsers and servers
Because it is an Internet service, the World Wide Web is based on clients and servers. A World Wide Web client is called a web browser or simply a browser, and a World Wide Web server is called a web server or sometimes just a server. Browsers and servers on the World Wide Web use a set of communications rules called HTTP (HyperText Transfer Protocol).

A browser is a program that navigates the World Wide Web and displays pages. The browser requests a page from a server based on its Internet address. It retrieves the document from the server and displays the contents. The most used browsers are Microsoft's Internet Explorer and Netscape Navigator which both can be downloaded from the net for free.

Note:
HTML tags and attributes are interpreted differently by different types of browsers. The appearances of the various page elements may differ from browser to browser. However, the structural relationship between elements will be the same - table cells will be inside their rows and headings will appear larger then the paragraphs that follow them.

A server on the World Wide Web stores pages and sends them to a browser when requested. Web servers are not simply file servers, however. They also run programs called CGI (Common Gateway Interface) programs or CGI scripts, based on the request from the browser.

CGI scripts run on the server and usually return some HTML for the web browser to display. For example, when a user fills in a form on a page, to register for a service, the form is often processed by a CGI script that could:

 

Hyperlinks
A hyperlink is a connection from a World Wide Web page to another file on the World Wide Web. The destination of the hyperlink is most often another World Wide Web page, but it can also be a multimedia file or even a program.

Hyperlinks are embedded directly in text or images on a page, and they give textual or graphical clues about where they lead. For example, a hyperlink phrase like "The State of Insanity" and the State's logotype both would indicate a link to the page.

Browsers usually underline text hyperlinks and display them in a specific color. Hyperlinks in images are invisible. However, users can tell when their pointer is over a hyperlink, because it changes appearance, usually to a pointing hand.

When a user clicks on a hyperlink to a page, the browser gets the page from the correct server and displays it. When a user clicks a hyperlink to another type of file, the browser gets the file and opens it in a associated program. For example, most browsers open .WAV files in a sound playback application.

 

URL
An URL (Uniform Resource Locator) gives the address of a file on the World Wide Web and also identifies the Internet service, such as FTP or the World Wide Web, that will handle the file. When a hyperlink is inserted on a page, the hyperlink is encoded as a URL.

url.gif (8232 bytes)

  1. The first part of the URL is the protocol, which tells the browser the Internet service that will handle the file. A protocol is separated from the rest of the URL by a colon. Besides the "http://protocol" which indicates that the file is on a World Wide Web server there are some others. For example:
  2. The second part of an http URL is the network location, which is a unique name that identifies an Internet server. A network location has 2 or more parts, separated by periods, as in "soi.hyperchat.com".
  3. The third part of an http URL is the path. The path identifies the folder or file directory, containing the file. If a file is stored in the root folder of a server, its URL will not have a path.
  4. The fourth part of an http URL is the filename. If there is no file name, the browser looks for the default page, usually named: "index.htm".
  5. After the filename, an http URL can have a bookmark. A bookmark is a named set of zero or more characters on a page that can be the target of a hyperlink. When a browser hyperlinks to a bookmark, it displays the page starting at the location of the bookmark. A bookmark is preceded by a number sign character, as in: "http://www.sample.com/index.htm#start"

 

IP number

The IP address is an address assigned to every computer (also includes routers and switches and other devices) on the Internet to uniquely define them. No two computers can use the same IP address. However, one computer (or device) may have several IP addresses. A simple example would be a computer that serves as a host for multiple services in which case each service may have one or more IP addresses.

Your ISP (Internet Service Provider) may have a pool of addresses which is assigned dynamically as each person logs on. This address then becomes your address while connected. Once you disconnect that address goes back into the pool. These are called dynamically assigned IP addresses. You never know what yours will be until after connecting and it is quite unlikely to be the same next time you connect. In contrast when given a static IP address you have the same address always. This address is yours whether you are connected to the net or not. Of course, no one can find the IP address or the web page located on your computer unless you are connected.

The IP address consists of 32 bits often shown as 4 octets. For simplicity's sake we normally use the dotted decimal approach to describe the addresses in this form 212.240.225.204.

There are 2 kinds of IP numbers

  1. Static - the computer has the same IP number all the time.

  2. Dynamic - the computer's IP number varies from one online session to an other (dial up connections)


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