Path: dp-news.maxwell.syr.edu!spool.maxwell.syr.edu!drn.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed.icl.net!newsfeed.fjserv.net!newsfeed.freenet.de!fu-berlin.de!uni-berlin.de!not-for-mail From: "Alan" Newsgroups: comp.databases,comp.databases.object,comp.databases.theory Subject: Re: Demo: Modelling Cost of Travel Paths Between Towns Date: Thu, 11 Nov 2004 09:21:52 -0500 Lines: 55 Message-ID: <2vhas0F2lnpsgU1@uni-berlin.de> References: <4b45d3ad.0411071807.4cbd51f0@posting.google.com> <18c7b3c2.0411081414.2f0f8b8e@posting.google.com> <4b45d3ad.0411082243.624f22db@posting.google.com> <419101ca$0$197$edfadb0f@dread11.news.tele.dk> <4b45d3ad.0411101154.2df356d5@posting.google.com> <419297f4$0$254$edfadb0f@dread11.news.tele.dk> X-Trace: news.uni-berlin.de 6xqxSrd5wDucDg0gFH6/YgA2ZULpUNRVrW0sPgTNi3LjWfp8hX X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.2800.1437 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1441 Xref: dp-news.maxwell.syr.edu comp.databases:41750 comp.databases.object:12756 comp.databases.theory:28071 "Ja Lar" wrote in message news:419297f4$0$254$edfadb0f@dread11.news.tele.dk... > > "Neo" ... > > > Upon further reflection, while not taking away from the apparent fact > > (I haven't verified it) that ISO-8601 mentions the existance of 24:00, > > there is no 24th hr in a day and therefore ISO-8601 is wrong! > If you haven't verified it, how can you know that ISO-8610 is wrong? > A day certainly has a 24th hour, as a day has 24 hours. The 24th hour begins > just after 23:00. > > >The time > > in a day can be described by t, where 0:00 <= t < 24:00, and does not > > include 24:00. > Whow, you are a genius. Thank you for pointing out that t<24:00 does not > include 24:00. > Now, what about 12:00 AM and 12:00 PM? > As much as we all like to gang up on Neo, he is actually correct on this point. We say a day has 24 hours, but it doesn't. First, we should get our terminology correct. We know that astronomically speaking, a day does not have 24 hours- it is slightly more- but let's ignore that, as it is not important to the problem. Let's also ignore the philosophical discussion regarding time that will inevitibly lead us off topic. Let's deal with the day-to-day reality of how we deal with time as we know it. According to ISO, we can assign the value 0000 or 2400 to midnight. Let's look at another time, say 2 PM, or 1400 . Do we assign two values to 1400? No. Nor do we do so for any other time. Why? because each time designation represents exactly one point in, well, time- as it must. Now, for the sake of simplicity, let's measure time by days, hours, minutes, seconds and hundredths of seconds (to avoid extending to the infinite decimal place). Day 1 begins at 00:00.00 and ends at 23:59.99. Note that this must mean that Day 2 begins at 00:00.00. To conform to the notion that each point in time is indicated by one value, there is either no time value of 24:00.00 OR there is no time value of 00:00.00. To have both of these is assigning two different values to one and only one point in time. The ISO standard, though widely adopted (it is a standard, after all) is incorrect. The reason midnight gets two values is to make it easier to calculate elapsed times, and to clarify what one means when using the term "midnight". The problem of calculating elapsed times without the use of 0000 and 2400 is trivial, so that reason is not a terribly good one. The other reason, clarity of meaning, also does not hold. If the ISO midnight standard was really a clear expression of a particular point in time, it would be easily understood, and insurance contracts would not have to read 12:01 a.m. No, I do not think we should do away with the standard (it's too late now), but let's not pretend it is correct in its represenation of reality.