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Re: What are units-of-measure? e.g., what's a "kilometer"?

• To: "Roger L. Costello" <costello@m...>
• Subject: Re: What are units-of-measure? e.g., what's a "kilometer"?
• From: Alaric B Snell <alaric@a...>
• Date: Thu, 17 Jul 2003 17:50:29 +0100
• Cc: xml-dev@l...
• In-reply-to: <3F16D271.729E37F2@m...>
• References: <OF14C8EB10.34A02CDE-ON80256D66.004C964A-80256D66.004CDB06@c...> <3F16D271.729E37F2@m...>
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Roger L. Costello wrote:

> This is quite a radical approach.  I am surprised that there
> aren't more comments, since the "conventional wisdom" is
> not to treat kilometer as a property/relation/function, but rather
> to treat it as the value of a property, e.g.,
> 
>   <River id="Yangtze">
>        <length unit="kilometer">6300</length>
>   </River>

The advantage of "<kilometres>6300</kilometres>" as opposed to <length 
unit="kilometre"> is in modularity of type definition.

With the unit= approach, you're probably saying that the type of length 
is an attribute that can be km/miles/nautical miles/etc, and a value 
which is a number.

However, if you want to allow other types of length measurement - non 
numerical ones such as giving the name of another object of the same 
length, say - then with the latter approach your 'type' might need to 
widen to include any value as the distance, not expressing the fact that 
for kilometres it'd better be a number, while if you have a 
"<kilometres>" element then you can state that it contains an integer 
while a "<same-as>" element contains a string.

However, smarter type systems let you define types in terms of things 
like "distances where unit='kilometres'" and thus allow you to organise 
it however you want, so it becomes a moot point.

I find "unit=''" more pleasing on the eye, myself.

> Thoughts?  /Roger

ABS

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