Re: Temporal database - no end date
Date: 19 Jan 2007 12:42:20 -0800
Message-ID: <1169239340.938970.215230_at_s34g2000cwa.googlegroups.com>
V.J. Kumar wrote:
> So, how do you model your continuous time if all you have is at best a
> subset of rational numbers (IEEE 754) ?
Le sigh.
I am making a very, very narrow claim. I would appreciate it if you
read what I wrote, and addressed your questions to it.
My technical observation is that using chronons to discretize time
implies that mathematical operations over temporal quantities lose
information. My snarky remark was to the effect that many people on
> >Models of time that divide the continium into
> > discrete units, and then force all intervals, aggregations and the
> > results of any operation into that model, just don't work.
>
> Really ? How come that people do it all the time by using digital
> computers that do not have real numbers ? All the computers have are a
> subset of integers and a subset of rationals ?
They either don't, or they do it badly. How do you propose to compute the variance of a temporal random variable using integers? This is no academic question, or corner case from obscure scientific applications. It's a basic question that comes up regularly in industrial and OR applications all the time.
I'm perfectly happy to make the necessary engineering compromises and use doubles precision types in my algorithms, mindful of the joys that come with 'thinking about precision'. Alternatively I could-- and have before -- opt to use one of the quite sophisticated open source math packages that support arbitrarily large integers, and whatever rational numbers can be expressed using ( INTEGER / INTEGER ) ( a perfectly reasonably domain which can be implemented in most of the modern SQL DBMS engines).
NONE of which is relevant to the question of whether my temporal domain is better off modelled as a sequence of discrete units, or points on a continium. Received on Fri Jan 19 2007 - 21:42:20 CET