Use the sophisticated management and monitoring features of the Oracle Database
Diagnostic and Tuning packs within Oracle Enterprise Manager that include the
Automatic Database Diagnostic Monitor (ADDM) and AWR.
The above words comes from oracle official document. Oracle 11.0.2.3 Oracle Real Application Clusters Administration and Deployment Guide. I was always wondering what on earth ADDM and AWR are. And this paragraph gives a good overview.
Here is my understanding. Oracle EM has an commponents called Oracle Database Diagnostic and Tunning packs. ADDM and AWR belongs to this pack. Appreantly the pack is used to monitor and tunning the database performance, so ADDM and AWR should also be designed to do it.
The Oracle Database Performance Tuning Guide describes the Oracle Database automatic features for performance diagnosing and
tuning, including ADDM.
This sentence also comes from the documents. So if you want to have better understanding of ADDM check that document.