Page 14 - DCAP408_WEB_PROGRAMMING

Web Programming

Notes A browser consists of a set of clients, a set of interpreters and a controller that mange them. The
controller forms the central piece of the browser. It interprets both mouse clicks and keyboard
inputs, and calls other components to perform operations specified by the user.

Example: When you press a link, the controller will call a client to fetch the requested
document from the remote server, and an interpreter to display the document for the user.
Besides an HTTP client and an HTML interpreter a browser can contain components that enable
the browser to perform additional tasks. Many browsers include an FTP client that is used to access
the file transfer service and an e-mail client that enable the browser to send and receive mail.
The user doesn’t invoke such services explicitly; instead, the service is invoked automatically, when
it is needed to perform a task. For Example, file transfer can be associated with a selectable object on
the screen, when a user selects the item the browser uses the FTP client to obtain a copy of the file.

How to Access the World Wide Web — Web Browsers

There are two types of browsers:

1. Graphical: Text, images, audio, and video are retrievable through a graphical software
program such as Netscape Navigator and Internet Explorer. These browsers are available
for both Windows-based and Macintosh computers. Navigation is accomplished by
pointing and clicking with a mouse on highlighted words and graphics. The current
version of Navigator is contained within a suite of programs called Netscape
Communicator. You can install a graphical browser such as Netscape Navigator in your
Windows-based or Macintosh machine. Navigator is available for downloading on the
Netscape home page: http://home.netscape.com. To use the program to access the Web,
you need an Ethernet connection or a dialup connection known as a SLPP or PPP. The latter
may be obtained from an Internet Service Provider. For more information, see How to
connect to the Internet.
2. Text: Lynx is a browser that provides access to the Web in text-only mode. Navigation is
accomplished by highlighting emphasized words in the screen with the arrow up and
down keys, and then pressing the forward arrow (or Enter) key to follow the link. This
browser is available through your personal IBM, VAX, or UNIX account on campus.

Extending the Browser — Helper Applications and Plug-Ins

Software programs may be configured to a Web browser in order to enhance its capabilities.
When the browser encounters a sound, image or video file, it hands off the data to other programs,
called helper applications, to run or display the file. Working in conjunction with helper
applications, browsers can offer a seamless multimedia experience. Many helper applications
are available for the free.

File formats requiring helper applications are known as MIME types. MIME stands for the
Multimedia Internet Mail Extension, was originally developed to help e-mail software handle a
variety of binary (non-ASCII) file attachments. The use of MIME has expanded to the Web. For
example, the basic MIME type handled by Web browsers is text/HTML associated with the file
extension.HTML.
A common helper application utilized on the Web is the Adobe Acrobat Reader. The Acrobat
Reader allows you to view documents created in Adobe’s Portable Document Format. These
documents are the MIME type application/pdf and are associated with the file extension .pdf.
When the Acrobat Reader has been configured to your browser, the program will open and
display the file requested when you click on a hyperlinked file name with the suffix .pdf.

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