[tz] Adding verified historic details

Lester Caine lester at lsces.co.uk
Thu Sep 5 12:58:14 UTC 2013

Alan Barrett wrote:
> Zefram has written a prototype of this code.
My problem with that statement is I am not convinced that a re-factoring of the 
data wouldn't be helpful in both tidying up the process of adding new data 
moving forwards, and incorporating extra history.

The current concentration on 'timezone' is to my mind ( now that I've been 
through the data ) the wrong way of working. We have 'rules' that apply over 
periods of time, and locations switch between those rules. NAMES are about 
identifying which set of rules to use, and if those rules were re-factored to 
add the arbitrary 1970-01-01 transition, would filtering be any easier? We just 
need to identify a unique set of rules for a period, and then link locations to 
those rules. Simply number the rules ( in database terms an autoinc identifier 
for the id ) and then many countries can use the same rule, or set of rules, and 
adding 'hot potatoes' is separated from managing the raw data?

As a practical example. Jersey Started using UK-GMT/BST time on a date, switched 
to 'German Time', switched back to UK-GMT/BST time and then to EU defined times. 
The bulk of the detail is in the rules which are shared, and the small amount of 
detail relates to the when rules changed. Once we can package rules in a way 
that can be filtered for valid use dates, filtering is easy, and then timezones 
available are those using the valid rules ...

Lester Caine - G8HFL
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