[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: limits of the generic
Hi Dare, > xs:duration is broken and should never have made it into the W3C XML > Schema REC in the first place. Simple question; Is an xs:duration > representing 3 months equivalent to an xs:duration representing 90 > days? According to the latest XPath 2.0 F&O WD, you can actually do xs:duration('P3M') = xs:duration('P90D') and if they're not "exactly equal" the answer is false. But I think that you're getting at the fact that it's undefined. I can think of several ways of dealing with that which don't rule out perfectly legitimate uses of durations that mix years or months and days or times: We could simply say that if it's undefined it's false (though I believe that this leads to optimisation problems because it means that it's no longer true that a values must be one of equal, greater than or less than another value): P3M = P90D => false P3M > P90D => false P3M < P90D => false We could introduce three-value logic: P3M = P90D => () P3M > P90D => () P3M < P90D => () We could ban direct comparisons of durations, forcing users to add them to dates in order to compare them: 2002-09-28 + P3M = 2002-09-28 + P90D => false 2002-09-28 + P3M > 2002-09-28 + P90D => true 2002-09-28 + P3M < 2002-09-28 + P90D => false Or we could use the current date/time automatically in a comparison like the above. Or we could pick a date in the past and use that consistently for all duration comparisons. Any of these would be better than making it an error for people to ask perfectly legitimate, and answerable, questions and introducing two new, more restrictive, data types that users have to use instead of xs:duration in order for their schemas to work with XPath 2.0. For example, I think that "What is 2002-09-28 plus a year and a day?" is also a simple question with a well-defined answer; I don't think it should be an error to try to ask it. Cheers, Jeni --- Jeni Tennison http://www.jenitennison.com/
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