On Tue, 28 Jan 2003, Peter J. Acklam wrote: > > [...] the fact that an ISO date can be expressed 6 different > > ways, which makes ISO less attractive to me. > > I don't see why this is relevant. A date may be represented in > many more than six ways, but as long as one picks one format and > everyone agrees to use that, then it's no longer a problem. > > The iCalendar format is much worse because it is too limited to be > suitable as a base format. It might be ok for everyday calendar > use, but not as a base format for a set of modules that might be > used by people with all sorts of needs related to range and > precision: Astronomers work with dates long before year 1 and > physicists work with atto, yotta, zettaseconds.
Date::ICal never used ICal format internally anyway, I should point out. > > Julian dates, for example, require that you store the time as a > > separate field, because the julian date expresses only the date. > > It is *very* common to include a fractional part to represent the > time of day. And by allowing an arbitrary number of decimals in > the fractional part (and an arbitrary number of digits in the > integer part) one can represent *any* point in time with *any* > precision. And Julian days are very convenient for time > arithmetic. And they are calendar independent -- a good "gratest > common divisor". > > Compared to Julian days, the iCalendar format is clumsy, awkward, > and limited. See above. Anyway, the current internals have Rata Die days (basically JD or MJD but with a different 0 day) and seconds into the day. Making seconds fractional is obviously not a big problem. At least one person object to fractional seconds (and preferred storing something like attoseconds separately) but I can't remember why. And it sure makes the implementation hairier. > > While I've read this various places, I've never encountered a > > real application where microsecond precision was necessary in a > > calendaring context. > > Is the DateTime-modules only for calendaring purposes? I thought > this was a base on which people could build modules for doing all > sorts of time calculations. Hm. Perhaps I misunderstood. I'd like it to work for lots of stuff, but if _all_ you need is attoseconds, then it's not going to be a very good fit. Do physicists need to record dates and times with attosecond precision, or do they need to record a date and time, and seperately record experiment data which includes attoseconds? See the difference? Making it work for calendaring purposes is definitely the first goal. If it can also be used for other things that is good. But what other things are you thinking of? -dave /*======================= House Absolute Consulting www.houseabsolute.com =======================*/
