>I think some of the confusion is that many folks think that RI must be enforced by a trigger mechansim, which is not true at all.

IMHO the issue here is one of data-validity vs data-integrity.. Saying value x must equal (or not equal) value y based on the value of z (or time of day, day of week, lunar cycle, etc) is a function of business rules.

RI on the other-hand says that this row cannot exist without a parent in another table, or we must delete all child rows when a parent is deleted etc.

RI is purely a function of relationships between entities in a database.. not the validity of the data held within the columns of non-RI columns.

Mark