Re: Counting propositions
Date: Tue, 15 Jun 2004 15:32:29 +0300
Message-ID: <40ceeb61$1_at_post.usenet.com>
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"Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote in message
news:cakuee$ak4$1_at_news.netins.net...
> When, if ever, should aggregate values be designed into base
This is a tough one. :-)
> Date uses a parts example, with a quantity, as an example relation in his
> relations?
Because being a base or a derived relation is accidental there is no rule.
:-)
The only rule I can think of is minimizing consistency checks.
> database textbook. By designing a quantity of a part into a relation,
there
> is an acknowledgement that you are designing aggregate data, rather than
> having a separate tuple for each real world part.
When there is no way to discriminate the "real world parts" by data in the
database.
> nr, in your example, is derived aggregate data. It is derived from the
Think about this. If you think you understood, think again.
> respect to a particular point in time, so that information needs to be in
> the resulting proposition in which nr is used.
Both derived and base aggregate data depend on the point in time.
> At <point in time> the count of distinct instances of <relvar> is <nr>
> I might be completely missing what you are getting at, however, so perhaps
> you could provide more clues?
Why someone would need to count "distinct instances of <relvar>" ?
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