[fitsbits] BINTABLE/TABLE column count limitation

[Mark Taylor]

On Thu, 7 Jun 2012, Forveille thierry wrote:

>   On 06/07/2012 06:42 PM, Mark Taylor wrote:
> > On Thu, 7 Jun 2012, Forveille thierry wrote:
> >
> >>    I concur with many that we first of all need a description of actual use
> >> cases, with considerably more motivation than someone coming up
> >> against error messages, possibly after doing something that's quite far
> >> from optimal (e.g. using many scalar columns for a vector).
> > As I tried to make clear in my initial message, this is not about
> > using multiple scalar columns where a single array column would be
> > more appropriate, it's about handling wide tables which do,
> > increasingly, exist in astronomy.  The PhotoObjAll table from SDSS
> > is 446 columns wide.
> The SDSS PhotoObjAll table actually is a quite good example
> of multiple scalar columns describing a vector/array reality:
> most parameters are defined from every bandpass (x5),
> the fit parameters have a multiplicity of a few, their covariance
> matrix of a bit more, etc...

I agree that it would be possible to collapse some of those scalar
columns into columns with values of short arrays.  I don't believe
that, for most purposes, it would be a good idea to do that, since
various operations on the data can become more unwieldy in that case.
At any rate, presenting the columns like that is the decision made by
the SDSS DB designers (who know a thing or two about making tabular
data available in usable form), and if you want to serialise database
tables or the results of queries on them, which I do, it makes sense
to reflect the table structure in the serialization format.

--
Mark Taylor   Astronomical Programmer   Physics, Bristol University, UK
m.b.taylor at bris.ac.uk +44-117-928-8776 http://www.star.bris.ac.uk/~mbt/