Re: relative complement?
Date: Sun, 27 Mar 2011 13:32:17 -0700 (PDT)
Message-ID: <ec2a8524-e841-45be-99f7-ce3102bc7a87_at_s11g2000yqh.googlegroups.com>
On 19 mrt, 01:30, paul c <anonym..._at_not-for-mail.invalid> wrote:
> I think you're no more biased than Date is when he advocates multiple
Paul,
D(&D)'s reasons for advocating multiple assignment are amply
documented, and they have _nothing_ to do with "persistence", on the
fly or not.
The thing is (, they say, ) let's assume that "temprorary
inconsistencies" (database states that are in violation of some
constraint) are allowed to be "seen" by the program that created
them. That is, let's assume that a scenario is possible in which a
program issues a DML statement DML1 that gives rise to an inconsistent
database state, then regains control, does whatever it sees fit to do,
then issues a DML statement DML2 that dispenses with the
inconsistency.
How can you guarantee that "whatever that program saw fit to do",
would not ultimately produce information that is (in whatever indirect
way) dependent on the inconsistency created, and how can you guarantee
that such information, "derived from an inconsistency", does and will
not propagate to other programs via mechanisms outside the control of
the DBMS (such as queues, pipes, sequential files, LU62
connections, ...) ? Such that the inconsistency will ultimately be
> assignment. I can see that you need some language feature like that if
> your chosen environment includes the ability to make relation values
> persistent on the fly.
> - Tekst uit oorspronkelijk bericht weergeven -