SQL Schema

Schema overview


The SQL schema has some differences from our Objectivity schema. Arrays cannot be represented in SQL Server, so we broke out the shorter, one-dimensional arrays f[5] as scalar fields f_1,f_2, The poor indexing in Objectivity/DB forced us to separate star and galaxy objects (for the 2x speedup), while in SQL we were able to merge the two classes and their associations. Object Associations were converted into Foreign Keys. Other than this, the schema conversion and data extraction and loading was remarkably easy.


The tables can be separated into several broad categories.

Photometric Observations

The first set of tables relate to the photometric observations.

Observation Hierarchy

Another set of tables is related to the hierarchy of observations and the data processing steps.

Spectroscopic Observations

Another set of tables is related to the spectroscopic observations. They capture the process of target selection and eventual observation.

Catalog Crossreferences

Finally, there is a table to capture cross-reference information about SDSS objects also detected in other catalogs, if a unique identification can be made. This cross-reference table can evolve as the need arises.

Peter Z. Kunszt, Alex S. Szalay, Ani R. Thakar, Jim Gray, Don Slutz
Last Modified: February 24, 2000.