I tried to use Business Object Mapper to map the table to a business object. I found that I only can select one table. Is it possible that business object can work with more than one tables? For example, a business object can select the fields from three tables.

I mean to create a view within the database that selects its fields from the separate tables.  You can then create a business object that will map to the columns of the view.  In answer to question #2, you cannot create a business object that can select fields from multiple business objects.  You would need to create a wrapper by hand that held the separate business objects.