[QUANTITY] Choosing default accuracy/units values

[Martin @ ROE]

Brian Thomas wrote:

> On Tuesday 18 May 2004 04:10 am, Pierre Didelon wrote:
> 
>>Hi Patrick,
>>
>>Patrick Dowler wrote:
>>
>>>I agree that default units and default accuracy/error should follow the
>>>same rules. However, to be successful the VO really needs to get people
>>>(force them if necessary) to not be lazy, so I would prefer making
>>>specification of units and accuracy mandatory (in the schema) and have
>>>some special values that can be easily used, like <unitless> and <exact>
>>>and <uknownUnits> and <unknownAccuracy>. There should be no default
>>>value.
>>
>>Isn't specila tag values <units>Number</units>, <accuracy>exact</accuracy>,
>><units>unknown</units> and <accuracy>unknown</accuracy> better  than
>>special tag names?
> 
> 
> 	I don't think so, in particular for the units. Having representation of individual
> 	values as elements (tags) makes it possible to more easily restrict "valid" 
> 	values for accuracy/units. Tags are more amenable to use within ontologies 
> 	as well.

Can't we do enumerations for values too? Consistent tags with special 
values would make it much easier to parse and marshall/unmarshall. 
Unless we do something like this:

<units>
    <unknown/>
</units>
<accuracy>
     <exact/>
</accuracy>

Which might give us the best of both worlds?

As an aside question: I always thought of ontologies as being some 
description/modelling combination - how do tags vs values make a difference?

Cheers,

Martin

-- 
Martin Hill
Software Engineer, AstroGrid (ROE)
07901 55 24 66