Re: A real world example

erk wrote:
> paul c wrote:
>> erk wrote:

...
>> Also (and I know I'm going a bit off-track here), saying a salary can't
>> be more than say, $10,000, might be thought of as a domain constraint,
>> not a relation constraint, but I think that would mean some
>> sophisticated type support in a dbms, eg. to come up with implications
>> using join. Whereas saying the salary must be less than such-and-such
>> if the job is clerk is more of a relation constraint.

> 
> What do you mean by "implications using join"? A domain mustn't be
> defined by reference to relvars.

I meant only that if I had Execs{Empdomain Emp,BigMoneydomain salary} and Clerks{Empdomain,PocketChangedomain salary} I might want to say Execs JOIN Clerks and get the result {Empdomain Emp, Allmoneydomain salary}, BigMoneydomain and PocketChangedomain are sub-types of Allmoneydomain. Maybe that's a bit contrived, but as I say, I'm weak on type theory - even if it's reasonable, I'm not sure the complexity is worth it for mundane apps.

p Received on Thu Aug 17 2006 - 20:05:05 CEST