Completeness and the Bind of Relation of Object/Relation Mapping

There are two ways of using object model.One way is, generally, accessing object model by the relation of the object, another way is, according to Relation theory, accessing or saving data by connecting tables or copying columns or rows. As the basal difference mentioned above,the integrate of two function is far from perfect. It is not match between OO design and relation data base design.So we need a mapping method——O/R Mapping to solve the inconsistency to get a successful design.