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Basic HTML
Relative Addresses
Let's use your homepage folder and files to illustrate
the difference between absolute and relative URL addresses.
Open your homepage folder and do the following:
- Create a new folder inside
your homepage folder; call it "gifs".
- Use the Browser to go to
the address
http://csep10.phys.utk.edu/next.gif.
Save the image that is displayed
into your homepage folder with the default
name "next.gif" by holding the right mouse button down
over the image, choosing "Save Picture as", and selecting
your homepage folder in the resulting dialog box.
- Use the Browser to go to
the address
http://csep10.phys.utk.edu/previous.gif.
Save the image that is displayed
in the folder "gifs" that you created inside your
homepage folder with the default name "previous.gif"
(NOTE: read the instructions carefully; this file goes
to a different folder than the one in the previous step!).
- Open your homepage file
index.html with the editor and insert the following
HTML code at a convenient place:
<h2> Examples of Absolute and
Relative URL's </h2>
This image has an absolute address
of "?":
<p>
<img src="?">
<p>
This is the same image displayed
with a relative address "next.gif":
<p>
<img src="next.gif">
<p>
Here is another image in a subdirectory
"gifs" of the present directory; it is
displayed using the relative address
"gifs/previous.gif"
<p>
<img src="gifs/previous.gif">
<p>
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Save the homepage file, but leave
the file open in the editor.
- Use "Open" from under the
"File" menu of your Web Browser to open the image "next.gif"
saved in your homepage folder. Copy the address displayed
in the "Address:" window of the browser with the mouse.
This is the (absolute) URL address of the file on your
machine. It will typically look something like:
file://c:/myfolder/next.gif
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(but the exact directory path will
depend on your machine). Go to the homepage file still
open in the editor and THE
TWO OCCURRENCES OF THE QUESTION MARK ()
WITH THE URL ADDRESS YOU HAVE JUST COPIED WITH YOUR
MOUSE. Save the homepage file, and close the editor.
Supplementary Note: The
preceding URL is the form for a URL address of a file
on the same machine as the browser. The "file://" part
tells us that. There then follows the absolute address
of the file on the machine. In the example given above
this is c:\myfolder\next.gif, which is the
sort of address you might see on a PC. On a Unix or
Macintosh computer, where the disks are generally designated
by names rather than letters, you might have a URL such
as file:///maindisk/myfolder/next.gif, where the file
has an absolute address of /maindisk/myfolder/next.gif.
(The relation between URLs and file addresses is discussed
further here.)
Now display your homepage with the browser (reload if
necessary). Your browser display should show something similar
to the following:
Examples of Absolute and Relative
URL's
This image has an absolute address of "file://c:/webcourse/next.gif":
This is the same image displayed with a relative
address "next.gif":
Here is another image in a subdirectory "gifs"
of the present directory; it is displayed using
the relative address "gifs/previous.gif"
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These elementary examples illustrate the difference between
absolute and relative addressing, and how to implement relative
addressing for the two simple (but common) cases where the
file being addressed is either in the same directory as
the HTML file (the next.gif example), or in an
immediate subdirectory of the HTML file (the gifs/previous.gif
example). As we have noted above, it is generally advisable
to use relative addressing in your Web pages to increase
portability.
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