[tz] State of the tzdb

Lester Caine lester at lsces.co.uk
Tue Sep 3 11:43:40 UTC 2013

Stephen Colebourne wrote:
> We're a lot further forward now to regaining stability, but there are
> a few points still outstanding.
> 1) Should there be one zone ID in the main files (not "backward") for
> each inhabited ISO-3166 code?
> I've argued for this as a reinstatement of a rule of 16 years standing
> which is no more than common sense.
> Paul has argued against.

A debate on openstreetmap at the moment relates to the status of historic 
information in that database. Many people feel that if it does not currently 
exist on the ground, then it should be removed. It is a little of an academic 
discussion since the data will remain in the change logs anyway, but it's access 
to that data which is at question. The current proposal is that some data is 
archived to an openhistorymap which will allow the use of a 'date' to define 
what data is displayed, but in many cases the bulk of the main database needs to 
be combined with the small amount of history to create the final dataset anyway, 
so openhistorymap has to have a complete copy of the main map! You can't define 
a reason for NOT including something in the historic map.

Not to dissimilar to what we are talking about here? To my mind all that is 
missing is an 'end-date' when a legacy zone was merged with a current one? We 
need the 'backwards' data in the main database, so why not just have all the 
zone data with both start and end dates ... most of which are open ended, but 
some 'link' to other zones at a particular time point.

In the case of the IM data, the start of GMT is recorded as 30th March 1883, 
there is a little commotion about dates for 1921, and then the law is passed to 
use the English time changes from 1922 ( when we find a copy :) ), so the zone 
data is tagged as linked to GB at that time on. From the historic perspective 
there are separate documents approving the changes to 'time' with separate 
approval dates, but personally I'm happy THAT material is in an archive. It's 
just the initial facts that differ and it does not add much to complete the 
whole picture? I think many other mergers are a similar situation with just a 
small amount of extra data?

Turning the problem around, if new evidence is found that provides additional 
differences to the change from LMT to a standard time for parts of an existing 
zone ... the problem that Paul is worried about ... Adding a new couple of 
entries giving that detail and linking to the ongoing 'time thread' is just 
sensible to my mind. Identifying the extra zone may be more controversial but 
the evidence would have to provide a reason to include the data anyway? When you 
look at an historic date you get all the currently active zone names ...

Lester Caine - G8HFL
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