[QUANTITY] Justification for Matrix Quantities (Was: Re: [QUANTITY] Requirements and apology)

[Ray Plante]

On Thu, 30 Oct 2003, Brian Thomas wrote:
> What about a quantity that has dependence on another one. Consider 
> the search use-case that an astronomer is looking for all flux measurements
> of the visual band. Of course, the search should find those "atomic"
> quantities that are V-band fluxes, but it should *also* beable to find fluxes
> from other flux quantities which are described in terms of wavelength
> (e.g. F(lambda) ) and  where some part of their wavelength range overlaps 
> the visual band (300-700 nm). For these quantities F(l)=> F(300-700nm) == F.

One way to look at this use case is to say that the fluxes you are looking 
for are not "Quantities" per se but rather a higher level concept that 
perhaps derives from "Measurement" which can include the observed 
frequency.  The "Flux" contains a quantity that can hold the actual 
flux value; it also holds the quantity representing the frequency.  

The point here is that the dependency between these quantities is captured 
at a higher level.  It is not necessary to encapsulate them both within 
this simple thing we call "Quantity".  

cheers,
Ray