Re: Temporal database - no end date

NENASHI, Tegiri wrote:
> I only started to read about the chronon. The articles that I read say
> that the application defines the granularity of chronon. Some one asked
> why is it that you cannot utilize the granularity of smaller value, one
> minute but not one day ? I am interested to know your opinion.

  You can.

   But regardless of the granularity you select, the problem still arises.

   Let us introduce a 'chronon' which is the amount of time it takes a light quanta to traverse a proton (say). What is the mean value of a large number of such measurements? What is the variance? These values will include some fraction of a 'chronon' so defined.

> I work on Oracle and I can affirm that the DATE in Oracle is one second
> of granularity. You say that 0.8 of the quantum is impossible, 0.8 of
> the day is impossible but 0.8 of 24*3600 is possible. 1/7 of 1000 is not
> exact (142) but the error is < 0.1 per cent. Why one can not select the
> granularity of chronon to achieve the exactness ? You can say, go and
> use floating point, but floating point is not exact too.

  The DDL book makes no claims about implementation. Nor should it. It's a book that describes a logical model.

   First, get the logical model right. Then worry about the engineering compromises needed by the implementation.

> I read about Snodgrass, and Snodgrass, he uses the name of chronon too.
> I want to know why you think that the chronon is bad in mathematic sense.

  Quanta are not 'bad'. They are not 'good'. The argument I am making is merely that 'time quanta' (as described in the DDL book) represent an innappropriate model for temporal reasoning because modeling time as a continuum and temporal phenomenon using intervals over the continuum is more general. Received on Sun Jan 21 2007 - 22:32:32 CET