The easiest way to translate classes into tables is to make a one-to-one mapping (see Figure 9-2). I strongly recommend against this approach, yet it is done more often than you might realize. One-to-one mapping can lead to the following problems:
Too many tables: Most object-to-relational translations done with one-to-one mapping produce more tables than are actually necessary.
Too many joins: If there are too many tables, then logically there will be too many SQL join operations.
Missed tables: Any many-to-many association (e.g., Customer and Address) will require a third relational table ...