[tz] Recent conversions of zones to aliases

Stephen Colebourne scolebourne at joda.org
Sat Oct 4 10:15:50 UTC 2014

On 4 October 2014 01:04,  <random832 at fastmail.us> wrote:
> On Thu, Oct 2, 2014, at 19:34, Stephen Colebourne wrote:
>> This issue occurs because Joda-Time normalises all aliases to the
>> actual zone as per TZDB data.
> Why? Tzcode doesn't, and for a long time zic hardlinked them. The
> distinction between an alias and the "actual zone" is therefore clearly
> not designed to be significant or user-visible.

The key point to remember is that Joda-Time has been running for many
years and has striven very hard to retain backwards compatibility.
Converting aliases to their underlying zone has worked well over many
years, and is far from an unreasonable approach, as it reduces the
effect of older zones such as US-Pacific.

Unfortunately, the extent of the use of aliases has been massively
expanded by the current tzdb maintainer. As such, there are now
effectively two kinds of alias, ones in the main files and ones in the
backward file. Despite the fact that they look the same in the file
format, they have been changed to have different meanings.

>From Joda-Time's perspective it is a no-win. If I leave it as is users
will complain that they can no longer get an ID for their country (a
backwards incompatible change). If I stop mapping aliases to
underlying for files other than backward its also an incompatible
change. (Perhaps you can tell, I have high standards of

Once again, I remind everyone that the tzdb data is now used far far
beyond the C programs supplied by this project. It is wrong to assume
that everyone uses the data in the same way.


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