Explain how the object classes are mapped to tables.

Each object class maps to one or more than one tables in the database. The objects in the class may be partitioned horizontally or/and vertically. For instance, if class has many instances of which, a few are often referenced. In this case, horizontal partitioning may improve efficiency by placing the frequently accessed objects in a table, and the remaining objects in another tables. Similarly, if a class has attributes with different access patterns, it may help to partition the objects vertically.