[QUANTITY] Data Model for Quantity v0.5 - analogue absurdium

[Martin Hill]

David Berry wrote:

>>>I think we are not starting from nothing, or anywhere near nothing. There
>>>are already developed systems in regular use around the world which are
>>>similar to the proposed Quantity model. It must surely make sense to
>>>build on the existing experience rather than throwing it all away and
>>>starting back at the "bicycle" stage. You never reach the aircraft
>>>stage if you keep on throwing away previous experience.
>>
>>If we have a bicycle, do we say we will now build a new and super 'Car'
>>that will do all the things a bicycle does, and everything we now use
>>must be based around a car?
>>
>>We certainly need to keep *experience* in order to reach the aircraft
>>stage, but we *should* be throwing away everything *else*.   Trying to
>>build a jet fighter with bicycle technology will (very probably...) fail.
> 
> 
> Ummm... I'm loosing the analogy a bit here. Are you saying that the
> currently existing "Quantity-like" software is "bicycle technology"
> which we should junk? My point in raising the point that we already have
> such software was to show that the Quantity draft is not such a huge leap
> as may be thought.

I think the analogue applies well to all parts of what we are doing in 
the VO.  We should be thinking iteratively - trying something (bicycle 
technology) out, and then not being afraid to throw it away especially 
in these early two-wheeler days.  It seems that every time any new 
prototype is presented (VOTable, ADQL) it is siezed in a death grip that 
of course then destroys the prototyping/iterative model.

As for Quantity, I do think the concept of creating a single thing that 
will be the 'superclass' of all other things is inappropriate technology 
for the VO.  It was very common in the early OO days but has lost it's 
appeal as time and experience demonstrated problems with it (as you 
understand yourself I believe from a previous post - 'favor composition 
over inheritance').

As I understand it Quantity is now being defined as an interface (which 
is good), but it is becoming an extremely heavy interface defining so 
many things in such detail that it's really just becoming an 
all-encompassing container class, reintroducing the inheritance problems.

Cheers,

Martin


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