CAS Datasets (databases)
BestDRx (DR5 now, DR6 later this summer)
Latest, greatest calibration of the data
Photometric and spectroscopic objects
The default and most accessed (by far) dataset
TargDRx
The calibration from which spectroscopic targets
were chosen
RUNS
All the runs (processings) other than Best, Target
SegueDRx
New with DR6 (SDSS-II)