[QUANTITY] doc consistency

[Guy Rixon]

If we had unitless and a nil="true" attribute to express "unknown unit" then
we'd be nearer to established practice. In this case, there is no default; one
or other has to be present for the XML to be valid against its schema.

On Mon, 17 May 2004, Jonathan McDowell wrote:

>
> Pierre,
>
> : >  Many things are optional in the sense that if absent in the
> : >  serialization, their value is a special value indicating  the absence of
> : >  valid data.
> : Then unitless which correspond to the absence of data, because it is not needed,
> : not due to uncomplete knowledge of the quantity object, does not match
> : this def of default value.
>
> Perhaps I used the word 'valid' wrongly... I didn't really mean 'valid',
> I meant perhaps 'of the standard form'.
>
> Anyway the question is, if the special values of Unit are <unitless> and <unknown-unit>,
> which should be the default?
>
> I was arguing in favor of <unitless>, but probably it should be
> <unknown-unit>, since then lazy providers will not generate large
> amounts of data that is interpreted as <unitless> when really it is just
> <unknown-unit>.
>
> So we could make the default 'unknown' and keep <unitless> as a special
> value but not the default value.
>
> The counter-argument is that <unitless> is really common, especially
> for integer and string data. What do other people prefer?
>
>
>  Jonathan
>

Guy Rixon 				        gtr at ast.cam.ac.uk
Institute of Astronomy   	                Tel: +44-1223-337542
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