XM-Resource for unit conversion

Hello everybody,

For my diploma work I'm looking for a resource of a desciription of 
measurement units. For example there should be listed "inch" and then the 
multiplication factor to "meter"...

I've seen there are several discussions for standards underway, but so far it 
does not seem that a common schema has been aggreed at. 
However, I think there should be some kind of unit-description around. 
Does anyone know of any such resource? any hint are most welcome!
thank you!

david