Question

http://twitter.com/codinghorror
http://twitter.com/login

These both look like twitter accounts but the second one is not. It’s a system page.

How does twitter know that logout is not a username and how does it make sure that no user registers under a system page name that exist or that may come into existance in future?

Answer 1

In most url routing frameworks there is a precedence order for your routing rules. Usually fist come first serve, so that the first url patten that matches controls the url.

In this case lets say twitter had to routes defined

map.connect 'login', :controller => 'auth', :action => 'login'
map.connect ':username', :controller => 'user', :action => 'show'

The first route would match the url twitter.com/login , but when you type in twitter.com/coddinghorror it would fail to match the first route and then match the second.