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000015_gadia@cs.iastate.edu _Wed Sep 15 17:15:26 1993.msg
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Message-Id: <199309152215.AA02843@optima.CS.Arizona.EDU>
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(1.37.109.6/16.2) id AA04440; Wed, 15 Sep 93 17:15:26 -0500
From: Shashi K. Gadia <gadia@cs.iastate.edu>
Subject: Re: Ahn/Rick/Temporal element
To: rts@cs.arizona.edu (Rick Snodgrass)
Date: Wed, 15 Sep 93 17:15:26 CDT
Cc: tdbglossary@cs.arizona.edu
In-Reply-To: <199309152133.AA22828@boojum.cs.arizona.edu>; from "Rick Snodgrass" at Sep 15, 93 2:33 pm
Mailer: Elm [revision: 70.85]
>
>
> > From tdbglossary-sender Wed Sep 15 12:52:26 1993
> >
> > > A temporal element in one dimension is
> > > a union but NOT a set of intervals.
> > >
> > > Greetings.
> > > If a union is a set operator, doesn't a union of intervals
> > > result in a set (of intervals) ?
> >
> > No.
> >
> > > I don't see the significance of the distinction here.
> > >
> > This distinction is similar to: "a relation is not a sequence
> > of tuples rather a set of tuples. This distinction is
> > extremely important.
> >
> > A union of intervals is already a reduced object having
> > a unique representation, where as a set is not.
>
> Shashi,
> This discussion raises two questions in my mind. If I have
> three temporal elements, each containing one interval:
> A = [1..10]
> B = [11..20]
> C = [21..30]
>
> Then D= A union C is a temporal element containing two intervals.
>
> My question is, how many intervals are in E = D union B?
Example:
E = 1..10 U 5..23 U 21..30 U 6..24
Where as the above union is unique, the intervals chosen
to express that union is not.
>
> Also, if a union of intervals (a temporal element) has a unique
> representation, what is that representation?
Union exists as a unique and well defined
object. That is all what matters.
>
> > To me temporal
> > element (the concept) is the most primitive notion in
> > temporal databases.
>
> I agree with you that the concept of temporal elements is
> very important in temporal databases. Closure under union, etc., is
> a very nice property to have.
>
> Cheers,
> Rick
>