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   Re: [xml-dev] xml-dev@lists.xml.org

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On Wednesday 11 December 2002 14:59, Bill de hÓra wrote:
> Alaric B. Snell wrote:
> > The thrust of the ASN.1 types is really based on mathematical concepts
> > such as 'integer', though. Those are pretty damn universal and have
> > reached broad acceptance from particle physics up to the structure of the
> > human brain :-)
> Al,
> The nearest things to universals I know of in the sciences are PSI
> units of measurement (I think I've said this before here). I'm not
> aware of a standard markup for them :(
> See David Megginson's post for what might actually be useful to the
> aircraft industry - I observe it's closer to units of measurement
> than mathematatical/set theoretic notions of types us computer folk
> seem to be fond of.

Units of measurements are a layer above the computer-folk types, indeed... 
people haven't spoken of those issues so much historically (although note 
that Java has a URL type distinct from just using 'String' as many other 
languages do; I think that kind of distinction is useful for static type 
checking, totally aside from the fact that the URL class appears to be 
implemented in parsed form rather than as the string anyway)

I would define a (hopefully shared and universal) set of types of the form 
(excuse my ASN.1 syntax):

 -- A measurement, which is probably the wrong term but I'm using it to mean 
a real quantity with a unit. --
Measurement ::= SEQUENCE {
	value REAL

 -- The abstract notion of a numerical measure of temperature. This type
    clearly is structurally identical to Measurement but carries extra
    semantics in that it happens to be a temperature measurement --
Temperature ::= Measurement

 -- Unit: degrees Kelvin. Usable for absolute and relative temperatures. --
unitKelvin ::= OBJECT IDENTIFER { ... blah unique id ... }
TemperatureKelvin ::= Temperature CONSTRAINED BY (unit = unitKelvin)

 -- Unit: degrees Celcius... --
unitCelcius ::= OBJECT IDENTIFER { ... blah unique id ... }
TemperatureCelcius ::= Temperature CONSTRAINED BY (unit = unitCelcius)

> Bill de hÓra

A city is like a large, complex, rabbit
 - ARP


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