HTTP: The Definitive Guide

Fat URLs

Some web sites keep track of user identity by generating special versions of each URL for each user. Typically, a real URL is extended by adding some state information to the start or end of the URL path. As the user browses the site, the web server dynamically generates hyperlinks that continue to maintain the state information in the URLs.

URLs modified to include user state information are called fat URLs. The following are some example fat URLs used in the Amazon.com e-commerce web site. Each URL is suffixed by a user-unique identification number (002-1145265-8016838, in this case) that helps track a user as she browses the store.

...
<a href="/exec/obidos/tg/browse/-/229220/ref=gr_gifts/002-1145265-8016838">All 
  Gifts</a><br>
<a href="/exec/obidos/wishlist/ref=gr_pl1_/002-1145265-8016838">Wish List</a><br>
...
<a href="http://s1.amazon.com/exec/varzea/tg/armed-forces/-//ref=gr_af_/002-1145265-
                 8016838">Salute Our Troops</a><br>
<a href="/exec/obidos/tg/browse/-/749188/ref=gr_p4_/002-1145265-8016838">Free 
  Shipping</a><br>
<a href="/exec/obidos/tg/browse/-/468532/ref=gr_returns/002-1145265-8016838">Easy 
  Returns</a>
...

You can use fat URLs to tie the independent HTTP transactions with a web server into a single “session” or “visit.” The first time a user visits the web site, a unique ID is generated, it is added to the URL in a server-recognizable way, and the server redirects the client to this fat URL. Whenever the server gets a request for a fat URL, it can look up ...