[tz] Proposal: validation text file with releases
skeet at pobox.com
Mon Jul 13 20:43:49 UTC 2015
Okay, I've created
It allows you (well, someone who's got everything set up...) to compare and
- Joda Time
- Noda Time
- Java 8
Only Joda Time and Noda Time allow (and in fact require) a data version to
be specified. Obviously in order to compare data meaningfully, one has to
be using the same data in all places. That's the next thing to look at...
but they're all using the same output format, and the results are already
interesting in terms of some unexpected discrepanicies. I haven't had a
chance to look into them yet.
On 13 July 2015 at 16:06, Jon Skeet <skeet at pobox.com> wrote:
> Given that I've already found discrepancies (see "Discrepancies in time
> zone data interpretation") I'm going to go ahead and hack on this in purely
> pragmatic (read: short term) ways. I'll create a github repo just for this
> purpose and dump code in there - this is explicitly with the aim of
> encouraging a more permanent solution by proving value.
> Will post another message here when there's something worth looking at -
> I'll be initially looking at zdump output, Joda Time, standard Java, and
> Noda Time. Contributions from others for other languages/platforms will be
> very welcome.
> On 13 July 2015 at 14:46, Stephen Colebourne <scolebourne at joda.org> wrote:
>> FWIW, I think such a format would be very useful. Effectively, it is a
>> unit test for others to confirm that they interpret the rules the same
>> way as intended.
>> It is similar to what I produced when trying to demonstrate the amount
>> of change being caused by apparently "minor" changes to the data:
>> Any output of this type should indeed just consist of a simple text
>> file with ISO-8601 format timestamps.
>> On 11 July 2015 at 11:35, Jon Skeet <skeet at pobox.com> wrote:
>> > Background: I'm the primary developer for Noda Time which consumes the
>> > data. I'm currently refactoring the code to do this... and I've come
>> > some code (originally ported from Joda Time) which I now understand in
>> > of what it's doing, but not exactly why.
>> > For a little while now, the Noda Time source repo has included a text
>> > file, containing a text dump of every transition (up to 2100, at the
>> > for every time zone. It looks like this, picking just one example:
>> > Zone: Africa/Maseru
>> > LMT: [StartOfTime, 1892-02-07T22:08:00Z) +01:52 (+00)
>> > SAST: [1892-02-07T22:08:00Z, 1903-02-28T22:30:00Z) +01:30 (+00)
>> > SAST: [1903-02-28T22:30:00Z, 1942-09-20T00:00:00Z) +02 (+00)
>> > SAST: [1942-09-20T00:00:00Z, 1943-03-20T23:00:00Z) +03 (+01)
>> > SAST: [1943-03-20T23:00:00Z, 1943-09-19T00:00:00Z) +02 (+00)
>> > SAST: [1943-09-19T00:00:00Z, 1944-03-18T23:00:00Z) +03 (+01)
>> > SAST: [1944-03-18T23:00:00Z, EndOfTime) +02 (+00)
>> > I use this file for confidence when refactoring my time zone handling
>> code -
>> > if the new code comes up with the same set of transitions as the old
>> > it's probably okay. (This is just one line of defence, of course -
>> there are
>> > unit tests, though not as many as I'd like.)
>> > It strikes me that having a similar file (I'm not wedded to the format,
>> > it should have all the same information, one way or another) released
>> > alongside the main data files would be really handy for all
>> implementors -
>> > it would be a good way of validating consistency across multiple
>> > with the release data being canonical. For any platforms which didn't
>> > to actually consume the rules as rules, but just wanted a list of
>> > transitions, it could even effectively replace their use of the data.
>> > One other benefit: diffing the dump between two releases would make it
>> > what had changed in effect, rather than just in terms of rules.
>> > One sticking point is size. The current file for Noda Time is about 4MB,
>> > although it zips down to about 300K. Some thoughts around this:
>> > We wouldn't need to distribute it in the same file as the data - just
>> as we
>> > have data and code file, there could be a "textdump" file or whatever
>> > want to call it. These could be retroactively generated for previous
>> > releases, too.
>> > As you can see, there's redundancy in the format above, in that it's a
>> > of "zone intervals" (as I call them in Noda Time) rather than a list of
>> > transitions - the end of each interval is always the start of the next
>> > interval.
>> > For zones which settle into an infinite daylight saving pattern, I
>> > generate from the start of time to 2100 (and then a single zone
>> interval for
>> > the end of time as Noda Time understands it; we'd need to work out what
>> > that would take, if any). If we decided that "year of release + 30
>> > was enough, that would cut down the size considerably.
>> > Any thoughts? If the feeling is broadly positive, the next step would
>> be to
>> > nail down the text format, then find a willing victim/volunteer to
>> write the
>> > C code. (You really don't want me writing C...)
>> > Jon
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