[tz] Epic fail for DST fallback in hospital health records

Guy Harris guy at alum.mit.edu
Thu Nov 8 09:18:41 UTC 2018

On Nov 8, 2018, at 12:44 AM, Lester Caine <lester at lsces.co.uk> wrote:

> On 08/11/2018 08:26, Guy Harris wrote:
>>> I doubt there were any specifications and nobody thought about transferring patients across timezones.
>> This isn't an issue of transferring patients across timezones.  It's an issue of "what happens when the clock gets turned back?"
> THAT is exactly the sort of statement that causes problems with any developments.

THAT is exactly the sort of statement that you have managed to completely misunderstand.

What *I* am saying is that, even if you don't need to worry about patients transferred across time zones, that doesn't mean you don't have to worry about DST time shifts.  I.e., I'm saying that there are *more* things you need to worry about, not *fewer* things.

> It's just like the ones about historic time rules not being important.

No, it's not.  There are many situations in which historic time rules *aren't* important, and for which making the extra effort to make sure those rules are correct isn't worth it.  "The best is the enemy of the good", and if, for example, we were obliged not to release any of the tzdb data files without spending time making sure we had the right standard <-> summer time transitions for pre-1970 dates, we might not gotten around to releasing them at all.  Perhaps there are *some* for whom "no tzdb" is better than "a tzdb that doesn't claim to be authoritative for pre-1970 tims", but that's not the case for *all* users of the tzdb.

> If one DESIGNS systems these days to be able to handle common activity then the risk of unexpected problems is reduced?

In answer to your question (yes, it's a question, otherwise it wouldn't have a question mark at the end), *that* depends on how they're designed.

And there's no guarantee that dealing with multiple time zones is a "common activity" for all systems that have to handle standard <-> summer time transitions. 

> The hospital records problem is only partially fixed by bodging over the time change.

Nobody here is suggesting "bodging over" the time change.

And somebody could "DESIGN" a hospital records system that "bodges" cross-time-zone patient transfers by keeping local time and requiring that times be converted to hospital local time either manually or by entering a special "here's the time zone for this time" indication, so worrying about cross-time-zone patient transfers doesn't magically ensure that you use UTC and avoid issues with the clock going backwards.

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