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This has been a real problematic area in earlier attempts to transfer engineering information between applications. In a lot of the STEP proposals (I'm not a STEP expert so please forgive any inaccuracies), there was a desire/requirement/need to preserve exactly the user's specification of the value that was done at the expense of engineering apps that primarily just wanted the value in SI. Unfortunately, that meant that one had to include in the STEP file all the unit strings and their conversion factors to some base unit (and hope the file had some unit you could recognize as your base unit). I gets really complicated really quickly. Like in your example, most people would interpret mph as miles per hour, but somebody else could use it for meters per hour (or metres per hour). In complex dimensions, you could have thousands of reasonable permutations (whether to use dots between units, slashes or -1 for units in the denominator) Since in the types of apps I deal with only a very small fraction of "data" is user provided (and hence would have some value to preserve what the user type) and most of it is calculated (typically in SI or close to SI units), my approach is to have an attribute for the value in a fixed SI unit (and in a schema world it would be associated with a datatype that specified the unit) and if you want to preserve the users input then use the elements text data. So for speed it would be something like He was travelling at <Velocity value="1">3600 kph</Velocity> where value is defined as always being in meters per second. In schemas, I'd have a velocity datatype that was defined as being in meters per second. If you though it could add value, you could tag the unit. <Velocity value="1">3600 <UnitRef href="#kph">kph</UnitRef></Velocity> This also allows you to support really fuzzy user specified values that you could never hope to resolve by parsing the human presentation. You know how <Temperature value="289">cold it feels on a brisk fall morning</Temperature> (289K, 16C, 59F for those of you who don't think that Kelvin is the temperature unit of choice) -----Original Message----- From: Ronald Bourret [mailto:rbourret@i...] Sent: Thursday, July 15, 1999 2:55 AM To: 'XML Dev' Subject: RE: Units of measurement? Jeffrey E. Sussna wrote: > Does the XSchema datatypes spec support the notion of units of measurement? > In other words: > > element "x" is of type "speed", which can be in "mph" or "kph" > > A potential representation of this might be: > > <x units="mph">200</x> Sort of. What you can actually do is define a speed data type and say that the *units* attribute (not the x element) is of type speed -- that is, its value is either "mph" or "kph". You can also say that the x element must have a units attribute. Note that you can also do this specific example with DTDs, by defining units as an attribute with an enumerated type. (Nit: XSchema is the name of the predecessor of DDML. I believe you are referring to XML Schemas -- the schema language being developed by the W3C. Given the amount of confusion over these names, I'm beginning to wonder if we shouldn't donate the XSchema name to the W3C...) -- Ron Bourret xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1 To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...) xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1 To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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