Quantity - where does it fit?

[David Berry]

Martin,

> > We are not building a programming language, we are building a huge
> > application.
>
> With Quantity we are trying to build a modelling language that we can
> then express all our data models in.  That was really my point; we
> shouldn't be doing this.

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.

> 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