VOResource v0.8.2

[Patricio F. Ortiz]

On Fri, 26 Sep 2003, martin hill wrote:

> I shall take this opportunity to raise my own pet peeve: UCDs are not nearly
> enough for describing data properly, so that we can compare and combine data
> across different datacenters.

Agreed. What you can say is that if two data columns (whatever their origin
is) have the same UCD, the chances of them being "alike" (but not
identical) are very high. Astronomers do express things in different units,
eg, pc, AU, Km for distance, therefore, within any given UCD which uses
these units one needs conversion factors, which are workable.

Note that not all quantities which are measured in Km will belong to the
same UCD. Different physical quantities are measured in the same units!
eg, orbital velocity vs expansion velocity vs c(redshift)!

> But the registry does need one (or several) ways of describing data using a
> common 'dictionary' of some sort, and UCDs are the best we've got right now!

Dictionaries do exist, but getting people to agree on them is tough, plus,
ambiguities do exist and are hard to get rid of.

> It may be that not every column needs to be assigned a UCD
> (? what do people think?

Can you give some examples? Adding a label (UCD) to each column is a
democratic process. How do you choose the column's worthiness to receive a
UCD?

> ) but the ones that astronomers are likely to query on (the WHERE part of an
> SQL clause) will need them.

Unfortunately, "likely" is subjective. Once registries and services are
working we could build a UCD "ranking" and a "top 40" list of the most sought
quantities. Astronomy is fashion driven :-)

Cheers,

Patricio


---
Patricio F. Ortiz			pfo at star.le.ac.uk
AstroGrid project
Department of Physics and Astronomy
University of Leicester			Tel: +44 (0)116 252 2015
LE1 7RH, UK