Standardising units and formats (and ref frames?) in transmission

[Rob Seaman]

Sorry to keep copying both these lists...

On May 19, 2009, at 3:05 AM, Alberto Micol wrote:

> If there is no constraint on what data providers put on the wire,  
> then any VO client will have to deal with such complexity.

I guess I failed to make my point.  The complexity is inherent in the  
problem domain.  Either it is hidden from the users - in that case it  
must appear deeply embedded in the system.  Or it is evident to the  
users - in that case the complexity must appear in the user interfaces  
and utility tools.

> Can we imaging a software library that hosts all the receipes,  
> formulae, conventions, units, formats written in those books?  
> Obviously not.

Why obviously not?  Software must often map to complexity in the real  
world.  This complexity may not appear in a single library - perhaps  
in several and perhaps in tailor built application tools.  The  
alternative is to pretend that we are going to reengineer the practice  
of astronomy.  One is more skeptical at that prospect than of  
implementing the algorithms from the "Explanatory Supplement".

Software is good for specifying algorithms - one is almost tempted to  
assert that that is what software is designed to do.

> All that complexity is to be left to the specialist, to the  
> astronomer that knows what she wants in his (I'm bipartisan)  
> specific domain. The VO can perform only if that complexity is left  
> to the specialised astronomer.

Ok, so an astronomer has a list of sexagesimal coordinates.  Say the  
VO only accepts decimal degrees.  The astronomer needs a tool to  
manually perform the translation.  Somebody has to write that tool.   
One could (and users will) interpret the person who writes that tool  
as being a "VO programmer".  We simply can't escape these requirements.

> The VO can only help by passing around information in a standard way.

Indeed!  But this is a separate (and orthogonal) project requirement.   
Standardizing on as simple a set of interfaces as possible will  
clarify the VO system architecture, but it won't magically remove the  
complexity inherent in astronomy.

Rob