Re: Surrogate Keys: an Implementation Issue
Date: Sun, 30 Jul 2006 17:27:56 GMT
Message-ID: <w_5zg.74002$fb2.457_at_newssvr27.news.prodigy.net>
"paul c" <toledobythesea_at_oohay.ac> wrote in message
news:qt4zg.281144$IK3.267521_at_pd7tw1no...
> Brian Selzer wrote:
>> "paul c" <toledobythesea_at_oohay.ac> wrote in message >> news:zTOyg.269253$IK3.233927_at_pd7tw1no... >>> Brian Selzer wrote: >>>> "paul c" <toledobythesea_at_oohay.ac> wrote in message >>>> news:g9Nyg.263082$iF6.250988_at_pd7tw2no... >>>>> Brian Selzer wrote: >>>>>> What's the point of a database if it doesn't reflect some aspect of >>>>>> reality. ... >>>>> To talk precisely about whatever we want to talk about. Nothing more. >>>>> Doesn't need to be real. >>>>> >>>> Agreed. But even a conceived universe subsumes certain absolutes, such >>>> as time. >>>> >>> In that case, the statements in the database should talk about time, >>> ie., aspects of time. These are different from statements about the >>> time it takes the database to say something. >>> >> >> There can be no discussion without time. Relational assignment cannot >> exist without the concepts of before and after. ... >
> For some people, unfortunately, that is a matter of belief. In the
> context of RT, I'd say it is mere willfullness. To see why, try to avoid
> the words 'before' and 'after', using say, x and y instead to stand for
> two relations (which might be the same). To ask which one (or two) does
> the db state at this moment in time is the same as asking does it state x
> or does it state y. But to ask which one(s) was stated yesterday requires
> that we deliberately add time information. This is a choice that allows
> us to ask the second question. The point is that we may not be interested
> in the second question and choose not to state information about time
> which makes the use of a time concept arbitrary.
>
But the assignment operation by its nature determines the order of the states x and y: one must always precede the other because the operation itself produces that other.
> Maybe the confusion arises from Codd mentioning 'time-varying relations'.
> In the interest of making his main points in an efficient way, I suspect
> he didn't want to dot every last 'i'. As soon as you talk about
> relational assignment you are talking about variable replacement, aka
> pointer replacement. Logical replacement doesn't require any notion of
> time. Nor does algebraic difference.
>
Could you please elaborate on that? Replacement, as I understand it, subsumes that something exists and will be superceded by something else. Algebraic difference isn't even related to assignment. Difference is an operator, assignment is an operation. I don't understand why you included it. Perhaps you're conflating the concepts of operator and operation.
> You might as well say that relational assignment cannot exist without the
> concepts of the seven other dimensions that string theorists talk about.
> Some of them admit those dimensions are philosophical - in the RT context,
> I call it mystical. Like the book of Genesis - apparently the first day
> had a morning and an evening, on the fourth day the Sun was created! Just
> because that mysticism won't go away doesn't mean we must accept it in RT.
>
> p
> > >
>
Received on Sun Jul 30 2006 - 19:27:56 CEST