Root Cause Analysis History

Currently Vitrage deletes alarms that are deactivated.
Once we have a persistent graph database, we would like to store deleted alarms, together with their causal relationships. Then, the user is able to detect the root cause of a problem that was already solved (or partially solved; for example, a host fault was fixed, but an application running on one of its instances failed to recover),

There are a few aspects to consider:
* The logic of root cause representation. If A caused Z, then B caused Z, then A went down... how to represent it?
* Implementation: is storing a big graph the solution? root cause relationship can be stored in other ways as well
* UI representation. How to display the root cause relationship on a time line