Re: Surrogate Keys: an Implementation Issue
Date: Sun, 30 Jul 2006 15:44:22 GMT
Brian Selzer wrote:
> "paul c" <toledobythesea_at_oohay.ac> wrote in message
>> 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.
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.
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 - 17:44:22 CEST