Oracle: Minimum database implementation

I am a definite dba wannabe; however, opportunities to study come few and far between. One of the things that I keep forgetting is what is mandatory and what is optional on a database instance. Hopefully, now I'll be able to keep track of that:

Minimum database implementation

1. External structures
   1. One or more data files.
   2. One or more control files.
   3. Two or more online redo logs
2. Internal structures
3. Memory structures (SGA)
   1. Data block buffer cache
   2. Redo log buffer cache
   3. Shared sql pool
4. Background processes
   1. SMON
   2. PMON
   3. DBWR
   4. LGWR
   5. CKPT
   6. User processes associated with PGA