Oracle Database Discussions

Hello DBAs,

I have some trouble with understanding Average Active Sessions graph in Oracle Enterprise Manager. First of all I don`t quite understand the scale on Y axis. How those values are calculated and what actually do they mean?
There are also some categories of activity that I find hard to interpret. When I see that graph is high in System IO, CPU Used or User IO sections, I know that database is using a lot of host resources. But what are Applications, Configuration or Administrative categories? Yesterday I had some high activity on a production database in Application category, but the appliaction that uses database was running quite smoothly.

Thanks in advance,
P.