Re: Date, Darwen, Pascal and the alternative to Nulls in the RM
Date: 23 Mar 2006 09:15:30 -0800
Message-ID: <1143134130.259128.181350_at_g10g2000cwb.googlegroups.com>
JOG wrote:
If a user enters data into an sql database in the following manner:
(primkey(soc), name, age grade)
their logical meaning should be:
now in a logically consistent system, a query for soc, name, grade
should return the following:
> Paul Mansour wrote:
> > Assume one accepts, as I do, the argument against nulls put forward by
> > Date et al. Would it be fair to say that at this point in time they
> > really don't have a solution to missing information?
> > anything better. Am I wrong here?
> [huge snip of interesting stuff]
>
> They propose a system that decomposes all relations down to irreducible
> tuples (hence eradicating nulls). The horrendous joins and
> consequential problems this might leave are handled by their closed
> source "transrelational model (tm)" in a manner which currently eludes
> my recall. As far as I know this system is yet to see the light of day.
[111-11-1111, jim, 21, A]
[222-22-2222, joe, null, C] <==no age available for joe
[333-33-3333, jack, 23, B]
[111-11-1111, jim]
[111-11-1111, 21]
[111-11-1111, A]
[222-22-2222, joe]
[222-22-2222, C]
[333-33-3333, jack]
[333-33-3333, 23]
[333-33-3333, B]
(notice missing entry [222-22-2222,null] <=joe has no age)
[111-11-1111, jim, A]
[222-22-2222, joe, C]
but the query for soc, name, AGE, grade should return the following???:
[111-11-1111, jim, 21, A]
[333-33-3333, jack, 23, B]
Notice the missing [222-22-2222, joe, null, C] entry since this tuple
doesn't evaulate to TRUE (due to the null), it can not be part of any
result set.