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2.3 Naming Scheme for HTML Documents

When your HTML browser (Mosaic, TkWWW, Lynx .....) retrieves a file it must know what to do with it. Hypertext servers (HTTP servers) explicitly tell the browser the type of the data being sent. In other cases, such as when the browser is using FTP or local file access, the browsers guesses the data type from the filename extension -- that is the part after the dot in the filename. Thus HTML files are identified by name.html, where the .html extension marks an HTML document.

Four letter extensions are common. This is not a problem with UNIX computers or Macintoshes, since these machines place no restriction on the filename. DOS machines are unfortunately restricted to a three letter extension. Generally the extension is truncated to three letters (i.e. .html becomes .htm). But, I must point out that I do not have a PC to work with so I do not know how general this rule is.

Here are some of the standard extensions, and their meanings:

.html
HTML document, containing text and HTML mark-up instructions.
.txt or .text
A plain text file. The browser presents the file as a block of text and does not process it for mark-up instructions. Note that the browser will assume a file to be a text file if nothing else is appropriate.
.gif
A GIF format image file.
.xbm
An X-Bitmap (black&white) image file.
.xpm
An X-Pixmap (colour) image file.
.jpeg
A jpeg-encoded image file.
.mpeg
An mpeg-encoded movie file.
.au
An aiff-encoded audio (sound) file.
.Z
A compressed file - compressed using the adaptive Lempel-Ziv coding. This compression/decompression program are commonly found on UNIX computers.
.gz
A compressed file - compressed using the GNU gzip program. This program is common on UNIX computers and is available on PCs and Macintoshes.
The World Wide Web uses MIME types (Multipurpose Internet Mail Extension) to define the type of a particular piece of transferred information. A browser in turn determines, from the MIME type, how the data should be treated. Each browser has a configuration (menu or file) that maps types of files to particular functions. Some types it can handle itself, while other types are passed to auxiliary programs, such as image or movie viewers, sound players, and so on.

HTTP servers attach MIME contents-types headers messages to every file they serve to the browser, so that the browser knows what type of file it is and what to do with it. For more information on MIME types see the MIME RFC Document.

If a browser gets a file from a non-HTTP server it guesses the MIME type from the extension, as described above. It then uses the configuration database (menu or file) to determing what it should do with this type of data.

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