Let me give you an example. Let's say you have a site with over 50 pages and you need to add another link to your navigation bar. Can you imagine how long it would take you to open each page and update it? By putting your navigation bar into an SSI file, you would only open up that one file and update that -- and the change to your navigation bar will show up site wide. See how simple that was? By editing one file you have updated your entire site instantly.
The most common use of an include file is for your top navigation, your bottom text navigation, copyright, logo or any other piece of info needed to appear on all pages of your site.
So how do you create an SSI file? Glad you asked! An include file can be an HTML file or a simple text file. It should be whatever HTML coding you need for that element of your site, minus the <HTML> or <Body> tags which should remain on your individual pages.
An easy way to make them is to design your web page and cut and paste the code you want into individual files and name them things like topnavigation.htm or bottomnav.htm. By giving them descriptive names, you'll know at a glance which file is which when it comes time to perform those updates.
After creating the files you plan on using as your includes,you'll need to open your web pages and insert a line of code where you want the SSI information to show up in your documents.
The code looks like this:
<!--#include virtual="nameofSSIfilegoeshere.htm" -->
If your includes are located at the root level on your
web server your path would look like this:
<!--#include virtual="dropdownmenu.htm" –>
That's it. Pretty simple, really. After you get the hang of it you'll wish you would have learned about them years ago. They really do make global updating a snap.
Here are a couple of good sites to learn more about SSI:
Big Nose Bird-
New Breed Software
Before you start implementing SSI you need to ask your web host if they support them (most do), and also if they will need to be named with any special extensions. Some servers may require you to give them specific extensions like .asp (if it's NT) or .shtml (for many Unix servers). Although the majority won't, it's always better to ask first. Better safe then sorry.
By designing your website with server side includes you'll save yourself a ton of headaches when it comes time to updating your site. SSI is a Webmaster's best friend, so I suggest you spend some time getting acquainted.