Re: Temporal database - no end date

Kev wrote:
> Thanks for taking the time to reply Bob.
>
> For everyones benefit I assume you are talking about the book
>
> Temporal Data & the Relational Model,
> First Edition, C.J. Date, Hugh Darwen, Nikos Lorentzos
> (Morgan Kaufmann, 2002);
> ISBN 1-55860-855-9
>
> I will take a look.
>
>
> Does anyone know if I might find formal answer to my original question
> in this book, or anywhere even?
>
> Thanks all.
>
> Bob Badour wrote:
>
>

>>If you are satisfied with SQL kludges, then I suppose Snodgrass is okay.
>>If you are interested in something more robust, I suggest you google
>>Lorentzos and check out the Date, Darwen, Lorentzos material.

A number of ways exist to model the problem of open intervals. In the Date/Darwen/Lorentzos book, they opt to make all intervals inclusive. To model an open interval in that system, one would use the largest representable value as the end of the interval, which for practical purposes is the same as the other methods.

One might choose to separate the starts and the ends of intervals into separate relations. In that model, a start without a subsequent end or an end without a prior start would indicate open intervals. However, one immediately encounters a number of problems. For example, one will generally have to resort to a lot of special cases to make use of the open intervals, and one will find it difficult--if not impossible--to express many common constraints. Received on Tue Jan 16 2007 - 16:08:07 CET