BOM in purchase order

Hi experts,

Is it possible to use the BOM in purchase order? In the sense, if material a = b + c, then If i create the purchase order for material a, it should explode to b and c as the BOM explodes in a sales order.

Please let me know if this possible? And if yes, then how to go about it? If no, what is the reason we cant use it in PO?

- Prashant