Re: Category Types

>> They [modern RDBMS] does not support foreign constraints like
REFERENCES (tableA or tableB or tableC). <<

You need to know exactly what set of values are referenced.

A reference cannot be one of many different kinds of things. We need a relationship between a car and an owner. A car is defined by its VIN (Vehicle Identification Number, ISO- 3779 standard) and a VIN is easy to verify. An owner is a legal concept; it can be a person, corporation, church, etc, (what we call a "lawful person"). But he/she/it has certain attributes when they act as an owner. They have an address for legal purposes, they have the title to the car, etc. We do not care about other attributes -- what sex is your bank :)?

We discussed this "Pendant clause" in the X2H3 Database Standards Committee years ago and found problems with circular references and domain violations. I do not remember all of the details, but the problem was that you could not get a table as a result. One row would have more columns than another.

>> P.S. sorry for my English <<

Better than my Russian!

--CELKO-- Received on Wed Jun 18 2003 - 21:05:21 CEST