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Re: Surrogate Keys: an Implementation Issue

From: Brian Selzer <brian_at_selzer-software.com>
Date: Sun, 30 Jul 2006 17:27:56 GMT
Message-ID: <w_5zg.74002$fb2.457@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 - 12:27:56 CDT

Original text of this message

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