URI and URL ?

i want to know the difference between URI and URL.

URL is usued when i need things like "http://www.yahoo.com"

but where do i use URI ?

To get a clear idea on this please refer http://www.w3.org/TR/uri-clarification/#contemporary.

Hi, the link's explanation is diiificult . they are also showing some research papers. is it a difficult concept ?

can you explain it in few simple words ?

This site will give you more clear idea.
http://www.bernzilla.com/item.php?id=100

hi, i have read the link and collected badly grasped information.

my collected information :
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1. URL's are subset of URI. all URL's are basically URI.

2. URL is usued for network address. but people will forget it very soon and start using URI because its the superset.

3. there is no use of URI nowadyas. No body use it though java has a class named URI. but its useless.