Re: 3 value logic. Why is SQL so special?
Date: Wed, 13 Sep 2006 01:17:17 GMT
Message-ID: <x_INg.532276$Mn5.145502_at_pd7tw3no>
JOG wrote:
> Paul wrote:
>> "JOG" <jog_at_cs.nott.ac.uk> wrote: >>...
> The illogic of using nulls has been covered to death in the literature.
> Surely you ought have read it given your job?
> ...
Right. If I may go further, if a single 'table' is seen as desireable for some reason, AFAIAC, actual departure time can be safely deemed to be equal to estimated departure time until the biz rules dictate that a plane has departed. I say 'biz rules' because the purpose of the system should dictate interpretation, not the viewpoint of an objective observer. I don't think this violates any RM principle.
Some misconceived queries might use actual departure time to determine that a flight has departed (note the word 'flight' as opposed to 'airplane', this is a common abstraction in the airline biz', one of the few that makes sense, along with 'flight segment'), but the writers of those queries should think twice, assuming that the purposes of the schema have been explained to them. After all is said and done, a schema is an arbitrary abstraction, the fact that this is so is what allows us to make systems that are models of other systems.
p Received on Wed Sep 13 2006 - 03:17:17 CEST