How to proceed to rate an application ?

Hello,

We would like to put in place a new rating of the applications under IT responsibility to allow us to implement an efficient Problem Management process. This would replace the current approach which is based on only one parameter (criticality) and not on the users impact, market connectivities, …
Ideally I would like to have at the end a rating which allow us to put in place a realistic view on our set of applications.

Thanks in advance for the potential hints.