# RE: Units (inches and centimetres, etc)

From: Danny Ayers <danny666@virgilio.it>
Date: Mon, 16 Jun 2003 18:18:04 +0200
To: "Graham Klyne" <gk@ninebynine.org>, "RDF interest group" <www-rdf-interest@w3.org>
Message-ID: <BKELLDAGKABIOCHDFDBPKEAEDBAA.danny666@virgilio.it>
```

> I find myself wondering if the proposals for unit conversions are
> slightly
> missing a deeper, more pervasive issue.
>
> A statement to the effect that 1 inch is 2.54 centimetres I think has two
> important parts:
>
> (a) a universally quantified assertion;  e.g. forall x, x inches is the
> same as f(x) centimetres, for some specified f.  This seems a bit like a
> "rule" to me.

Very much so.

> (b) arithmetic relations:  the function 'f' alluded to above
> being defined
> in terms of common arithmetic operations.
>
> (I observe that similar case not amenable to a simple conversion factor
> would be to express the equivalence of temperatures expressed in
> Fahrenheit
> or Celsius scales.)

Yep, I think the problems start occurring pretty soon past this example.

> To date, RDF has not standardized any form or arithmetic
> relationship.  Means to represent numerical values are relatively new,
> currently proposed by RDFcore.  CWM has built-in properties that
> correspond
> to arithmetic relationships [1].
>
> This suggests to me that we don't really need anything new that isn't
> already being done.  There's a lot of activity devoted to the development
> of rules [2] [3].  It seems that there already exists a design for RDF
> properties dealing with relations based on arithmetic operations [1],
> though I could see a case for making that work a little more
> "forceful" --
> e.g. by publication as a W3C Note, with a view to taking it to the
> recommendation track in future RDF working groups.

I think cwm is wonderful, but I'm not sure how far it should be considered a
role model. Being able to plugin a procedure at the drop of the hat is
sweet, but unless that procedure is made explicit then everything could get
very shaky. Being able to call on a reproducible algorithm/process/service
to carry out a conversion is one thing, having it be a black box is another.
Personally I'd favour drawing a line in the sand around simple comparisons
(==, > etc) applied to typed literals which could form a little package of
quasi-builtins for use with rules. Where any f beyond this is needed then I
think this would be best viewed as a service, even if it is carried out
locally as Chaals suggested.

Cheers,
Danny.
```
Received on Monday, 16 June 2003 12:21:42 UTC

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