In the simplest case, a
program object of class A has fields x, y, z and a table B has columns x, y, z
◦Each instance of A has a row in B and vice versa, via ORM
◦Are we done?
◦If x is a unique id, and x, y, and z are simple types,
yes.
◦--Or some unique id in (x, y, z), possibly composite
If no unique id in (x, y,
z), the object still has its innate identity, but
corresponding rows involve duplicate rows, against relational model rules
So in practice, we add a unique id in this
case:
Class A1 has id, x, y, z and table
B1 has id, x, y, z