Re: Temporal database - no end date
Date: Sat, 20 Jan 2007 04:38:27 +0100 (CET)
Message-ID: <Xns98BDE68264822vdghher_at_194.177.96.26>
"DBMS_Plumber" <paul_geoffrey_brown_at_yahoo.com> wrote in news:1169244255.112697.246680_at_l53g2000cwa.googlegroups.com:
>> Could you show with an example how the loss occurs ? You may be >> right, but let's see.
>
> Suppose I have 5 things. 4 of them lasted for 1 'day' before they
> break.The other broke on the same 'day' it went out.
>
> What is the mean time to failure?
>
> Sum of 'time quanta' = 4.
> Number of things = 5.
>
> Mean time to failure = 0 time quanta.
>
> Pick any intuitive unit of 'time quanta', and you can construct an
> example where this problem arises.
This is funny. The chronon granularity is supposed to be application dependent in the temporal database. If you choose a granularity of one day instead of maybe one hour or one minute or one second, whose fault might it be if you get a result that you are not happy with ?
Older non-temporal databases do not have application dependent chronon granularity but it can be cooked up manually. For example in Oracle, it is one second (has been up until recently), but people have managed to make use of it with some success for many years !
>
>> You've answered that yourself below: by using home-made rational >> numbers or the prepackaged floating point numbers.
>
> Neither of which is the approach the Date, Darwen and Lorentzos
> book
> describes.
>
> They have a model of time where (from pp 62) "We need to
> distinguish
> carefully between time quanta as such, which are the smallest time
> units the system is capable of representing, and the time units that
> are relevant for some particular purpose, which might be days or
> months or milliseconds (etc., etc.). We call these latter units time
> points (or just points for short) in order to stress the fact that for
> the purposes at hand they too are considered indivisible. Now, we
> might say, informally, that a time point is a "section on the
> timeline" - in other words, the set of time quanta - that stretches
> from one "boundary" quanta to the next. .... Formally, however, time
> points are indeed points - they are indivisble, and the concept of
> duration strictly does not apply."
See ? You choose whatever makes sense, a year or microsecond quantum.
>
> The argument made in response to this is to point out that
> regardless of the logical size of the quanta selected, there will
> always be applications which reason about 'fractions of a quanta' for
> some purpose. And this 'quantum model of time' cannot represent that
> kind of reasoning.
For example, what applications ? Received on Sat Jan 20 2007 - 04:38:27 CET