Need Clarification on NewRecord

Hi All,
I have a following code snippet,

this.BusComp().NewRecord(NewAfter);
this.BusComp().SetFieldValue("Name","SomeValue");
this.BusComp().WriteRecord();

Now my question is,
How does Siebel selects the columns in the INSERT/UPDATE statements which is triggered during NewRecord?? In other words, what are the Fields in BC (or) Columns in Table that will be selected by default by Siebel while performing a NewRecord???

I could guess a few criteria like,
 - System Columns
 - Columns set as Required to Y
 - Fields set as Required to Y

Other than these are there any conditions???

Regards,
Maggi.