Re: Temporal database - no end date
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sat, 20 Jan 2007 09:52:12 GMT
Message-ID: <gDlsh.3013$1x.52424_at_ursa-nb00s0.nbnet.nb.ca>
>
>
> 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
> this list are perfectly happy to invoke the 'but the physical computer'
> dodge when it suits them, while objecting to it's use at other times.
>
>
>
>
> 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.
Date: Sat, 20 Jan 2007 09:52:12 GMT
Message-ID: <gDlsh.3013$1x.52424_at_ursa-nb00s0.nbnet.nb.ca>
DBMS_Plumber 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
> this list are perfectly happy to invoke the 'but the physical computer'
> dodge when it suits them, while objecting to it's use at other times.
>
>
>>>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.
You have contradicted yourself. First, you state that it is impossible to accurately model time as discrete points, and then you admit to using discrete points. Received on Sat Jan 20 2007 - 10:52:12 CET