Quantity - where does it fit?

[Martin Hill]

David Berry wrote:

> My perception of the Q in the document is that it is a general purpose
> building brick which is intended to be used *inside* other models, as
> necessary, to hold and describe n-d arrays of homoegenous values for a
> single (possibly compound) phenomenon. Are you saying that your perception
> of the doc is that it suggests that other data models should be created as
> *sub-classes* of Quantity? If so, I think the doc should be changed to
> clarify this.

Yes that is my perception!  If it's *not* the case then I shall breath a 
partial sigh of relief.  But discussion on this mailing list seems to 
reinforce the idea that not just 'leaf' items on the data model are to 
be Quantities, but also that complex compound objects such as SEDs are 
to subtype Quantities, ie:

> 
> 
>>But some filters/passbands are based on formulae rather than a set of
>>points.  So we need to make sure an SED can handle some Passbands that
>>are defined by an equation - the whole SED might be a mix of point
>>measures and formuale.  Trying to squeeze all this into a generalised
>>Quantity is going to hurt.
> 
> 
> A CoreQuantity used to hold a passband could define the passband either by
> storing a list of explicit transmission values, or by storing a Mapping
> which takes (say) wavelength as input and produces transmission value as
> output. So CoreQ should be able to handle the "formulae" case.
> 
> David


-- 
Martin Hill
www.mchill.net
07901 55 24 66