On 01.07.2015 16:00, Pierpaolo Bernardi wrote:
On Wed, Jul 1, 2015 at 8:17 AM, Markus Krötzsch
<mar...@semantic-mediawiki.org> wrote:
Dear Pierpaolo,
This thread was only about Julian and Gregorian calendar dates. If and how
other calendar models should be supported in some future is another
(potentially big) discussion. As you said, there are many issues there.
Let's first make sure that we handle the "easy" 99.9% of cases correctly
before discussing any more complicated options.
Lydia Pintscher in the starting email explained that there's a model
for calendars, and unfortunately this model could be (and has been)
interpreted in two ways (AFAIU).
My intention was to point out that one of the two interpretations is
not sound. This leaves the other one as the only viable one.
To clarify: the problem that Lydia discussed has occurred on another
(more technical) level. It is not about the question whether there are
further calendar models that are incompatible to Julian and Gregorian,
but about the two calendar models that are captured by what Wikidata
calls the "date" type. This type does not support dates that cannot be
converted into one another. This is the usual trade-off you have when
building a data-based system: you have to restrict the possible formats
to ensure that the resulting data is still usable. For example, we could
capture many more complex things and nuances of reality in free text,
but then we would not have Wikidata but Wikipedia ;-)
What is colloquially called a calendar date can be anywhere between
clearly defined time point to a rough suggestion of a relative time
frame. Wikidata already makes a lot of commitments towards a less strict
notion of "date", many of which are not fully supported and correctly
used now (timezones, "before" and "after" -- even the meaning of
"precision" is all but clear). Many of these features have been
implemented as a response to user queries for making date entry even
more general, to cover even more corner cases. For data consumers, this
makes the data much harder to use. It creates a cost for everyone. So
far, there is only the cost, and not the benefit (or is anybody using
"before" and "after"? Yet I have to deal with it when reading data!).
Let's first make use of what we have (this includes proper UI support
for timezone annotation and precision windows), before discussing even
more complex notions of calendar and time.
But don't worry: there will surely be more calendar models that can be
supported properly, in a specified and clear way. However, it is
definitely not planned that all possible calendar models will at some
time be implemented. A basic design goal of the "date" type in Wikidata
is that dates remain compatible on the day level. Calendars that are too
far away from this should use own properties (maybe of type string,
maybe of another special date type). One can then give approximate
Gregorian/Julian dates in addition by using the standard date properties
of Wikidata (these approximate dates would then not capture the exact
moment, but the best possible approximation). In this way, one can get
the best of both worlds: exact date information in native calendar
models and maximal compatibility with major time-based applications
(such as Histropedia) and query services (all time-related query
functions in SPARQL databases are based on Gregorian dates).
Regards,
Markus
Cheers
P.
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