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Web Ch2- Introduction to WWW, Con't...

1.7 Web Pages

Information on the World Wide Web is stored in pages. A page can contain any of the following:
  • Text
  • Headers
  • Lists
  • Menus
  • Tables
  • Forms
  • Graphics
  • Multimedia

Web pages are plain text files constructed using HTML, the hypertext markup language. HTML is implemented as a series of easy-to-learn tags, or instructions. Web page author uses these tags to mark up a page of text. Browser then uses these tags to render and display the information for viewing.

HTML is constantly enhanced with new features and added tags. To ensure backwards compatibility, browsers must ignore tags they do understand. For example, if you were to use the <MARQUEE> tag to create a scrolling text marquee, browsers that do not support this tag will still display the marquee text, but it will not scroll.

Web pages can also contain typertext jumps which are links to other pages or web sites. Users can click on links to jump to other pages on the same sites or different sites.

The word "Web" in World Wide Web refers to this ability to jump to any web page on any web server, and back again.

Pages on a web server are stored in different directories. When requesting a web page, a user may provide a full path, or relative path to specify a particular document.

You can specify a default web page, a page that is sent back to the user when only a directory is specified, with a web server. This default pages are often called in index.html or default.htm. If no default web page exists in a particular directory, it will either return an error message or a list of all the available files, depending on how the server is set up.

1.8 URLs

Every web page on the World Wide Web has an address. This is what you type into your browser to instruct it to load a particular web page.

These addresses are classed Uniform Resource Locators (URLs). URLs are not just used to identify World Wide Web pages or objects. Files on a FTP server, for example, also have URL identifiers.

World Wide Web URLs are made up of up to five parts. These are:
  • The protocol to use to retrieve the object. This is always "http"
    • for objects on the World Wide Web.
  • The web server from which to retrieve the object. This is specified as a DNS name or an IP address
  • The host machine port on which the web server is running. If omitted, the specified protocol's default port is used; for web server this is port 80.
  • The file to retrieve or the script to execute.
  • Optional script parameters, also known as the query string

1.9 Web Browsers

Web browsers are client programs used to access web sites and pages. The web browser has the job of processing received web pages, parsing the HTML code, and displaying the page to the user. The browser will attempt to display graphics, tables, forms, formatted text, or whatever the page contains.

Web page designers has to pay close attention to the differences between browsers because different web browsers support different HTML tags. Unfortunately, there is not one single browser that supports every tag currently in use. Furthermore, the same web page often looks different on two different browsers because every browser renders and displays web page object differently.

For this reason, most web page designers use multiple web browers and test their pages in every one to ensure that the final output appears as intended. Without this testng, some web site visitors will not correctly see the pages you published.

1.10 CGI

    References

    (1) the Cold Fusion Web Application Construction Kit, Second Edition.
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