Address Book records for various business unit types

Hi All,

I have couple of  Qs around search types in Address Book:

1. Is it mandatory to have an address book record for a business unit (job or non job). If yes, what purpose does it serve?

2. Is there a defined mapping between address book search type and business unit type? Usually I have seen Search Type 'O' being used for companies, 'J' for Jobs. I wonder if each and every BU type has a corresponding search type.

Thank you.