DAL classes can be defined with respect to physical or logical business entities, BLL classes, as vice versa. This mapping process can include one to one, one to many or many to many technique.
For example, we have two business entities (physical or logical), named “Order Summery” and “Order Items” for an e-commerce application. Having a one-to-one mapping relation to DAL will contain, two separate DAL classes, as “OrderSummeryDAL” and “OrderItemsDAL”.