[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: ANN: a portable data component -- length
There are other potential problems too. Suppose, for example, that the measured distance is 1/3 mile. What do you put down so that the equations come out exactly right? Also, I would certainly want some indication as to which value was an actual measurement (there might be more than one) vs. which values were computed from the measurement(s), so I could distinguish between potential measurement errors and potential computational issues (roundoffs, etc.). On Apr 9, 2011, at 1:15 PM, Amelia A Lewis wrote: > On Sat, 09 Apr 2011 12:00:20 -0400, Liam R E Quin wrote: >> On Sat, 2011-04-09 at 11:10 -0400, Costello, Roger L. wrote: >>> Here is the altitude of an aircraft, expressed in both feet and meters: >>> >>> <altitude> >>> <feet>12000</feet> >>> <meters>3657.6</meters> >>> </altitude> >>> >>> It is important that the two length values are consistent: >> >> The right way to mark this up in most cases is to store only one value >> and convert as needed. >> >> See Normal Form in database theory: information should never be >> duplicated. That way it can't get out of sync. > > Agreed. My initial thought, on seeing the base post, was that this was > "How to generate problems in data synchronization", not "portable data > structures". > > By including two values in different units, rather than a single value > and relying upon the *well-known* formulae for conversion, all that is > achieved is to create doubt as to the accuracy of any reported value. > > As for the claim that the assertions will ensure that the data never > gets out of sync, poppycock. The initial statement is that the > information is 'portable', and yet this allegedly portable information > relies upon some external code that enforces assertion validity? And > what good do assertions do when these values *are* out of sync? Once > they've gotten out of sync (that is, at any stage of the process at > which someone fails to verify the assertions, or even any stage at > which someone uses a different degree of confidence, or uses a > different chain of conversions to generate values), *you don't know > which one is correct*. > > The following is valid: > > <altitude> > <feet>12000</feet> > <meters>4000</meters> > </altitude> > > ... within a certain degree of confidence. 1 m equals one yard > (rounding up; in some applications this is a perfectly valid > conversion). Now, it's highly unlikely that such an application > envisions measurements in thousands (at which point the > less-than-ten-percent conversion error has made for very large > differences), but ... in the above example, *which value is correct*? > > Or, to quote the storied wisdom of the ancients: a man with one clock > always knows what time it is. A man with two is never sure. > > Amy! > -- > Amelia A. Lewis amyzing {at} talsever.com > And now someone's on the telephone, desperate in his pain; > someone's on the bathroom floor, doing her cocaine; > someone's got his finger on the button in some room-- > no one can convince me we aren't gluttons for our doom. > -- Indigo Girls > > > > _______________________________________________________________________ > > XML-DEV is a publicly archived, unmoderated list hosted by OASIS > to support XML implementation and development. To minimize > spam in the archives, you must subscribe before posting. > > [Un]Subscribe/change address: http://www.oasis-open.org/mlmanage/ > Or unsubscribe: xml-dev-unsubscribe@lists.xml.org > subscribe: xml-dev-subscribe@lists.xml.org > List archive: http://lists.xml.org/archives/xml-dev/ > List Guidelines: http://www.oasis-open.org/maillists/guidelines.php >
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