What is the difference between empty default namespace and root name space in struts2.0?

If the namespace attribute is not defined in the package tag or assigned "" value then it is called empty default namespace.While if "/" is assigned as value to the namespace attribute then it is called as root namespace.

The root namespace is treated as all other explicit namespaces and must be matched. It’s important to distinguish between the empty default namespace, which can catch all request patterns as long as the action name matches, and the root namespace, which is an actual namespace that must be matched.