Re: relative complement?

On 27/03/2011 1:32 PM, Erwin wrote:
> 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
>> 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 -
>
> 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
> visible to the entire world nonetheless ?

Sorry, I should have said assignment, not multiple assignment. But I'll admit I do have multiple assignment on the brain or what's left of mine, mostly because of the sequencing requirement. Even when I've used merely procedural languages (ie., without multiple-assignment), I've always found putting statements in order to be the second-hardest and sometimes slowest part of it all (deciding what to do is the hardest part). What I like about multiple assignment is the idea of 'simulataneous' statements and I wonder why not have programs where all statements are simultaneous and statement order doesn't matter. Personally I think every dimension that can be removed from a programming language is to the good. I don't think I'd mind leaving it up to an environment to determine how a program's actions are to be recorded even if CJ Date might call that 'cheating'. Received on Mon Mar 28 2011 - 23:49:27 CEST