[appendix] handy info

Data types

From Dachs-Doc' columns definition, we have the following datatypes (non-exaustive)

type keyword	description
text	a string/char.
real	a real number.
double precision	a floating point number for high precision.
integer	typically a 32-bit integer.
bigint	typically a 64-bit integer.
smallint	typically a 16-bit integer.
timestamp	a combination of date and time.
date	a date. See timestamp.
time	a time. See timestamp.
box	a rectangle.

UCDs

From the list of all (1+ standard) UCDs, from IVOA's document, I highlight below some of (my) common use:

UCD	description	syntax code
meta.id	Identifier, name or designation	P
meta.record	Record number	P
meta.main	Main value of something	S
meta.ucd	UCD	Q
meta.unit	Unit	P
pos.healpix	Hierarchical Equal Area IsoLatitude Pixelization	Q
pos.eq.ra	Right ascension in equatorial coordinates	Q
pos.eq.dec	Declination in equatorial coordinates	Q
pos.eq	Equatorial coordinates	S
phot.mag	Photometric magnitude	E
phot.flux.density	Flux density (per wl/freq/energy interval)	E
stat.error	Statistical error	P
stat.error.sys	Systematic error	P

• Code “P” means that the word can only be used as “primary” or first word;
• “S” stands for only secondary: the word cannot be used as the first word to describe a single quantity;
• “Q” means that the word can be used indifferently as first or secondary word;
• “E” means a photometric quantity, and can be followed by a word describing a part of the electromagnetic spectrum
• “C” is a colour index, and can be followed by two successive word describing a part of the electromagnetic spectrum;
• “V” stands for vector. Such a word can be followed by another describing the axis or reference frame in which the measurement is done