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Original Message From: "Liam R E Quin" <liam@w3.org> To: "Costello, Roger L." <costello@mitre.org> Cc: <xml-dev@lists.xml.org> Sent: Saturday, April 09, 2011 5:00 PM Subject: Re: ANN: a portable data component -- length > > 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. > > So my answer is simply, "don't do this." > > Instead, e.g. > <measurement> > <name>altitude</name> > <value units="m">3657.6</value> > </measurement> I agree with the main thrust of your argument, but to me your final example seems little better than: <object> <name>altitude</name> <value units="m">3657.6</value> </object> I would say XML already has a notation for specifying what is a name and what is a value so there's no need to create an XML syntax that recreates that. I would rather do: <altitude>3657.6</altitude> and have it part of the definition that the value of altitude is always in meters, and in fact all lengths throughout the entire system are in meters. Possibly a bit utopian, but to do otherwise you take the risk of loosing space craft while entering the orbit of Mars! Pete Cordell Codalogic Ltd Interface XML to C++ the easy way using C++ XML data binding to convert XSD schemas to C++ classes. Visit http://codalogic.com/lmx/ or http://www.xml2cpp.com for more info Twitter: http://twitter.com/petecordell
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