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LAB 7.2 Exercises

7.2.1. Identify MIME Types, Helper Applications, and Plug-ins

a) Discuss why MIME types are necessary.

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A1:

Answer: MIME (Multipurpose Internet Mail Extensions) types are specific file formats that are recognized by MIME-compliant applications/programs such as Web browsers. Data files are usually identified as being of a particular type by means of a filename extension or suffix in the form “filename.extension.” By following this convention, a file extension identifies the format of a file so that an appropriate program or application can be used to process that file.

Keep in mind that after a Web browser requests a file via HTTP from a remote server, the first piece of data it receives is the MIME type of the file, which it then proceeds to compare to an internal listing of MIME types in order to determine what type of file is being sent and what should be done with it when it arrives. The browser's library usually includes a default list containing most of the more common MIME types; if they choose, users can manually configure the list, adding new entries or editing old ones as the need arises.

Assuming, then, that the MIME type of the received file corresponds to an entry on the list, the browser then does one of two things: It begins to process and display the file itself, as is the case with files of type image/jpeg or text/html, or it passes the file to a helper application or a browser plug-in, as specified by the list.

b) Investigate which MIME types are supported by your browser and how you specify new types.

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A2:

Answer: What MIME types your browser supports depends on both your operating system and browser. On Windows, the recognition of applications based on a file's extension applies to basically every application and not just the browser. The two most widely used browsers on Windows (Netscape Navigator and Microsoft Internet Explorer) will allow you to immediately start the application when you click on a link to a recognized file type. However, this is done using the file extension. For example, when clicking on a file ending in .DOC, the typical Windows behavior is to load MS.Word.

However, this is not what happens on other systems, such as UNIX. UNIX does not have the same concept of file endings as Windows. Therefore, UNIX browsers need to rely more on the MIME type.

Not all browsers let you define MIME types from within the browser itself. For example, MS-Internet Explorer is so tied into the operating system that the only way to define new types is through the operating system (i.e., File Manager). Netscape Navigator provides the ability to add new types directly from the browser.

While it may be unreasonable to expect that any Web browser could ever be able to open and process every single one of the hundreds of file formats in existence, it's only logical to expect that for every one of those file formats, there is at least one program, somewhere, that is capable of opening and reading it.

This is the fundamental concept behind helper applications.

c) A plug-in is a module that is run directly from the browser. Discuss the advantages of this as compared to a helper application.

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A3:

Answer: The idea behind plug-ins is similar to the idea behind helper applications: Essentially, they provide individual users with a way to selectively add functionality to their browsers, eliminating the need for developers to release the browsers already overloaded with features that most users won't actually need.

Unlike helper applications, however, plug-ins do not function independently of the Web browser. Instead of taking over for the browser whenever an unfamiliar file is encountered, a plug-in adds new capabilities to the browser itself, allowing the user to view additional content directly within the browser window.

Netscape introduced the concept of the browser plug-in with version 2.0 of its popular Navigator Web browser. Today, most browsers come with several plug-in modules already installed—usually sound or video players, such as Netscape's LiveAudio or Apple's QuickTime—and dozens of other plug-ins for use with various other types of content are available for free download from sites all around the Web.

7.2.2. Embed Sound in a Web Page

For this exercise, do a search on Yahoo for “sound clip archive.” This will give you a number of different sites with sound clips. Download a sound file (i.e., sound.au) from a site on the Internet.


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