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Re: temporary databases

From: Ruud de Koter <ruud_dekoter_at_hp.com>
Date: Mon, 27 May 2002 09:52:23 +0200
Message-ID: <3CF1E5B7.BE02F58C@hp.com>


Hi,

Mikito Harakiri wrote:
>
> After spending some time at
>
> http://dimlab.usc.edu/cs599-2000/
>
> I don't understand the elementary: what is the subject of temporal
> databases? Suppose we have a history table. Are there any queries that
> can't be expressed in standard SQL?
>
> Isn't interval just defined by a couple of trivial predicates t1<time
> and time<t2? What is the purpose of introducing interval datatype if
> it's not closed under union operator?
>
> According to Date/McGoveran a database is a repository of valid facts.
> Those facts are valid in *absolute* sence. We either say "Smith is
> teaching CS215 class" or say it more presizely "Smith was teaching
> CS215 class startind at 9am 10-Dec-1990 and ended at 9am 10-Mar-1991".
> If the second date is open-ended, it's just incomplete information.
> Wouldn't putting a null better than inventing some "transaction time"?
>
> Snodgrass p299: "We learn on Jan 26 that Exa bought the flat not on
> Jan 10 as initially thought, not on Jan3 as later corrected, but on
> Jan 5" -- only abstraction-challenged person can consider paragraph
> like that seriously. Just fix the data, not the model!

Never thought about the legal implications of knowing something at a given moment? Suppose someone is going to sue *you* for not saying that Exa owned the flat on Jan 7. It would be very interesting to know what you exactly knew at the moment you made the statement.

Still think this is a theoretical situation? Go talk with a real customer in the insurance business, or stock exchange.

Just as an aside: be a man, write under your own name.

Regards,

Ruud.
>
> Given a table of intervals answering a query what intervals cover that
> point is not trivial. Is this the only issue we could reduce temporal
> databases subject to?
>
> Clifford Heath <cjh_nospam_at_managesoft.com> wrote in message news:<3CED8250.D010727D_at_managesoft.com>...
> > This sort of database feature is useful of course, but (1) isn't necessarily
> > the most efficient way to handle historical queries (need to follow the log
> > chain back possibly many steps), (2) doesn't make it easy to identify
> > which history should be kept past log backup interval(s) and (3) prevents
> > revision of incorrect histories.
> >
> > There's still a need in many cases to model history explicitly.

-- 
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Received on Mon May 27 2002 - 02:52:23 CDT

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