SSA Primary Field

The SSA Primary Field is a system field on a business component that can be used to identify which MVG record is the primary. So if you use script such as: 

SetFieldValue("SSA Primary Field", "Y"); 

This will set the current MVG record to be the primary (the primary flag will be checked). 
What happens in the database is when this field is set on an MVG record the parent business component of the MVG has a field which is the primary id field for the MVG. This field holds the ROW_ID of the MVG record that is flagged as primary. 

So when the SSA Primary Field is changed in the database in the background an update is made on the parent table on the Primary ID Field to change the value to be the ROW_ID of the MVG record set as primary. 

To find what the Primary ID Field go to the parent business component > Multi Value Links > Primary ID Field. 

Therefore the SSA Primary Field explicitly is not stored in the database. 

For calculated fields, these are not stored in the database. When a business component is instantiated and the calculated field is to be displayed in the background Siebel will simply do an additional query in real time to obtain the calculated value, this not stored. This is why it is important to keep performance in mind when creating calculated fields that will be readily queried or force active. 

So the calculated field values are calculated at the point they are required.