If a table object to represents an SQL table
at some site, and an actual SQL table st exists
at that site, then st is called the target
of to.
That is to say, st is the target of to
when st agrees with to
on the following points:
An SQL table st is said to conform
to a table object to when:
st is to's target,
st has all the column names that to's
value mapper uses,
to's value
mapper expects,
NOT NULL constraints have the settings
that to's value mapper expects, and
st does not have any other columns.