Sloan Digital Sky Survey III SkyServer DR9

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Data Organization

The SDSS Catalog Data Model

The SDSS catalog data is stored in a commercial relational database management system (DBMS) - Microsoft's SQL Server. The data is therefore organized in several 2-dimensional tables. The tables and their relationships to each other are referred to as the schema in database jargon. The Schema link in the menubar above takes you to the Schema page where you can browse the database schema.

Diagrammatic view of the DR9 schema

There are 3 different types of data in the tables - imaging data is in the photo group of tables, spectroscopic and tiling data is in the spectro tables, and other data such as documentation or other information about the photo and spectro data, i.e. metadata, is in the meta tables. Some tables are also created specifically for speed or convenience, for example the SpecPhotoAll table, which contains a pre-computed JOIN of relevant fields in the PhotoObjAll and SpecObjAll tables.

The important tables are described below, along with the views that are currently defined on each table. A view is a subset of the corresponding table that can be used instead of the table - in other words it is a virtual table. A view is usually faster than using the base table, since it only loads a subset of the objects, but more importantly, the views we have defined on the tables select only the objects that are important for science, and they filter out non-science objects such as sky, QA or defective observations. As such, even though we list the base tables for completeness below, in the vast majority of the cases, you should use the views defined on the tables instead of the tables themselves, e.g. use the PhotoObj and SpecObj views for science instead of the PhotoObjAll and SpecObjAll tables.

Imaging (Photo) Data Tables

The important tables and views are described below. For each table, the views and indices are defined on that table are described in brief. For more information, please see the Table Descriptions help page and the Schema Browser.

1. PhotoObjAll - By far the largest table in the database, PhotoObjAll contains the 100+ parameters for each imaging (photo) object. For most of these parameters, there are actually 5 rows each, one for each wavelength band. This table includes data on all photo objects, not just science objects, hence the name PhotoObjAll. The view of this table that includes only science objects and excludes sky and other unknown objects is the PhotoObj view. The PhotoObjAll table is there for completeness, but science queries are usually done on the PhotoObj view.

   PhotoObjAll Views:

View Name	Contents	Description
PhotoFamily	These are in PhotoObj, but neither PhotoPrimary or Photosecondary.	These objects are generated if they are neither primary nor secondary survey objects but a composite object that has been deblended or the part of an object that has been deblended wrongfully (like the spiral arms of a galaxy). These objects are kept to track how the deblender is working. It inherits all members of the PhotoObj class.
PhotoObj	All primary and secondary objects in the PhotoObjAll table, which contains all the attributes of each photometric (image) object.	It selects PhotoObj with mode=1 or 2.
PhotoPrimary	These objects are the primary survey objects.	Each physical object on the sky has only one primary object associated with it. Upon subsequent observations secondary objects are generated. Since the survey stripes overlap, there will be secondary objects for over 10% of all primary objects, and in the southern stripes there will be a multitude of secondary objects for each primary (i.e. reobservations).
PhotoSecondary	Secondary objects are reobservations of the same primary object.
PhotoTag	The most popular columns from PhotoObjAll.	This view contains the most popular columns from the PhotoObjAll table, and is intended to enable faster queries if they only request these columns by making use of the cache. Performance is also enhanced by an index covering the columns in this view in the base table (PhotoObjAll).

PhotoObjAll Indices:

Index Type	Key or Field List
primary key	objID
foreign key	Field(fieldID)
covering index	mode, cy, cx, cz, htmID, type, flags, ra, dec, u, g, r, i, z
covering index	htmID, cx, cy, cz, type, mode, flags, ra, dec, u, g, r, i, z
covering index	htmID, run, camcol, field, rerun, type, mode, flags, cx, cy, cz, g, r
covering index	field, run, rerun, camcol, type, mode, flags, rowc, colc, ra, dec, u, g, r, i, z
covering index	fieldID, objID, ra, dec, r, type, flags
covering index	SpecObjID, cx, cy, cz, mode, type, flags, ra, dec, u, g, r, i, z
covering index	cx, cy, cz, htmID, mode, type, flags, ra, dec, u, g, r, i, z
covering index	run, mode, type, flags, u, g, r, i, z, Err_u, Err_g, Err_r, Err_i, Err_z
covering index	run, camcol, rerun, type, mode, flags, ra, dec, fieldID, field, u, g, r, i, z
covering index	run, camcol, field, mode, parentID, q_r, q_g, u_r, u_g, fiberMag_u, fiberMag_g, fiberMag_r, fiberMag_i, fiberMag_z
covering index	run, camcol, type, mode, cx, cy, cz
covering index	ra, [dec], type, mode, flags, u, g, r, i, z, psfMag_u, psfMag_g, psfMag_r, psfMag_i, psfMag_z
covering index	phototag
covering index	parentid, mode, type

Field - This table contains all the measured parameters of each imaging field, along with relevant summary statistics, and astrometric and photometric information.

Field Indices:

Index Type	Key or Field List
primary key	fieldID
covering index	field, camcol, run, rerun
covering index	run, camcol, field, rerun

PhotoProfile - This table contains the light profiles of SDSS photo objects.

PhotoProfile Indices:

Index Type	Key or Field List
primary key	objID, bin, band
foreign key	PhotoObjAll(objID)

FieldProfile - This table contains the light profiles of SDSS field objects.

FieldProfile Indices:

Index Type	Key or Field List
primary key	fieldID, bin, band
foreign key	Field(fieldID)

Neighbors - SDSS objects within 0.5 arcmins and their match parameters are stored here. Make sure to filter out unwanted PhotoObj, like secondaries.

Neighbors Indices:

Index Type	Key or Field List
primary key	objID, NeighborObjID
foreign key	PhotoObjAll(objID)

First, RC3, Rosat, TwoMASS, TwoMASSXSC and Usno - These tables contain matches between the FIRST, RC3, ROSAT, 2MASS, 2MASSXSC (2MASS Extended Source Catalog) and USNO survey objects respectively and SDSS.

Spectro/Tiling/GalSpec/SPP Data Tables

The important spectro, tiling, galSpec and spp (Stellar Parameter Pipeline) data tables are described here. The tiling table names are prefixed by "sdss" to distinguish them from tiling tables for BOSS (Baryon Oscillation Spectroscopic Survey) data in the future. For more information, please see the Table Descriptions help page and the Schema Browser.

1. PlateX - This table contains data as exported (the X is for exported) from a given plate used for spectroscopic observations. Each plate has 640 observed spectra and hence 640 corresponding entries in SpecObjAll.

   PlateX Indices:

   Index Type	Key or Field List
   primary key	plateID
   covering index	htmID, ra, dec, cx, cy, cz

2. SpecObjAll - This is a base table containing ALL the spectroscopic information, including a lot of duplicate and bad data. Use the SpecObj view instead (see below), which has the data properly filtered for cleanliness.

   SpecObjAll Views:

   View Name	Contents	Description
   SpecObj	A view of Spectro objects that just has the clean spectra.	The view excludes QA and Sky and duplicates. Use this as the main way to access the spectro objects.

   SpecObjAll Indices:

   Index Type	Key or Field List
   primary key	specObjID
   foreign key	PlateX(plateID)
   covering index	htmID, ra, dec, cx, cy, cz, sciencePrimary
   covering index	BestObjID, sourceType, sciencePrimary, class, htmID, ra, dec
   covering index	class, zWarning, z, sciencePrimary, plateId, bestObjID, targetObjId, htmID, ra, dec
   covering index	targetObjID, sourceType, sciencePrimary, class, htmID, ra, dec
   covering index	ra, [dec], class, plate, tile, z, zErr, sciencePrimary, plateID, bestObjID

3. SpecPhotoAll - The combined spectro and photo parameters of an object in SpecObjAll. This is a precomputed join between the PhotoObjAll and SpecObjAll tables. The photo attibutes included cover about the same as in the PhotoTag view. The table also includes certain attributes from the Tile table.

   SpecPhotoAll Views:

   View Name	Contents	Description
   SpecPhoto	A view of joined Spectro and Photo objects that have the clean spectra.	The view includes only those pairs where the SpecObj is a sciencePrimary, and the BEST PhotoObj is a PRIMARY (mode=1).

   SpecPhotoAll Indices:

   Index Type	Key or Field List
   primary key	specObjID
   foreign key	SpecObjAll(specObjID)
   covering index	objID, sciencePrimary, class, z, targetObjid
   covering index	targetObjID, sciencePrimary, class, z, objid

4. sdssTileAll - Contains information about individual tiles on the sky.

   sdssTileAll Views:

   View Name	Contents	Description
   sdssTile	A view of sdssTileAll that have untiled=0	The view excludes those sdssTiles that have been untiled.

   sdssTileAll Indices:

   Index Type	Key or Field List
   primary key	tile
   foreign key	sdssTilingRun(tileRun)
   covering unique index	tileRun, tile
   covering index	htmID, racen, deccen, cx, cy, cz

5. sdssTiledTargetAll - This table stores information that keeps track of why a Target was assigned to a Tile.

   sdssTiledTargetAll Views:

   None found

   sdssTiledTargetAll Indices:

   Index Type	Key or Field List
   primary key	targetID
   covering index	htmID, ra, dec, cx, cy, cz

6. sdssTilingGeometry - This table contains geometrical information about tiling regions, including tiling boundaries. The TileBoundary view serves up the boundaries.

   sdssTilingGeometry Views:

   View Name	Contents	Description
   sdssTilingBoundary	A view of sdssTilingGeometry objects that have isMask = 0	The view excludes those sdssTilingGeometry objects that have isMask = 1. See also sdssTilingMask.
   sdssTilingMask	A view of sdssTilingGeometry objects that have isMask = 1	The view excludes those sdssTilingGeometry objects that have isMask = 0. See also sdssTilingBoundary.

   sdssTilingGeometry Indices:

   Index Type	Key or Field List
   primary key	tilingGeometryID
   foreign key	sdssTilingRun(tileRun)
   foreign key	StripeDefs(stripe)

7. sdssTilingRun - Contains basic information about each run of the tiling software.
8. sdssTilingInfo - Contains information on what happened to a Target in a run of tiling software.
9. galSpecExtra, galSpecIndx, galSpecInfo and galSpecLine- These tables contain the estimated physical parameters, the spectral index measurements, general information about the spectroscopic analysis and the emission line measurements from the MPA-JHU spectroscopic catalog.

   galSpecExtra Indices:

   Index Type	Key or Field List
   primary key	specObjID

   galSpecIndx Indices:

   Nothing found

   galSpecInfo Indices:

   Index Type	Key or Field List
   primary key	specObjID

   galSpecLine Indices:

   Index Type	Key or Field List
   primary key	specObjID

10. sppLines and sppParams- These tables contain the line and paramater measurements from the Stellar Parameter Pipeline.

    sppLines Indices:

    Index Type	Key or Field List
    primary key	specObjID

    sppParams Indices:

    Index Type	Key or Field List
    primary key	specObjID

Galaxy Zoo Tables

There are the results of galaxy classification from the Galaxy Zoo site:

1. zooConfidence - Measures of classification confidence from Galaxy Zoo.
2. zooMirrorBias - Results from the bias study using mirrored images from Galaxy Zoo.
3. zooMonochromeBias - Results from the bias study that introduced monochrome images in Galaxy Zoo.
4. zooNoSpec - Morphology classifications of galaxies without spectra from Galaxy Zoo.
5. zooSpec - Morphological classifications of spectroscopic galaxies from Galaxy Zoo.
6. zooVotes - Vote breakdown in Galaxy Zoo results.

BOSS Galaxy Product Tables

There are a few new tables for derived data products from the Baryon Oscillation Spectroscopic Survey. They each have a primary key index on specobjid.

1. emissionLinesPort - Emission line kinematics results for BOSS galaxies using GANDALF.
2. stellarMassPassivePort - Estimated stellar masses for BOSS galaxies using photometric method, assuming passive model.
3. stellarMassStarformingPort - Estimated stellar masses for BOSS galaxies using photometric method, assuming a star-forming model.
4. stellarMassPCAWisc - Estimated stellar masses for BOSS galaxies using PCA technique.

Metadata and Other Tables

1. DBObjects - An auto-generated documentation table that contains a description of every object (table, view, function, stored procedure) in the database.
2. DBViewCols - An auto-generated table containing a description of every column in every table in the database.
3. DBColumns - An auto-generated table containing a description of every column in every view in the database.

The Hierarchical Triangular Mesh (HTM)

We have build a spatial indexing scheme called the Hierarchical Triangular Mesh (HTM) that spatially decomposes the region of the sky that is covered by the SDSS data and enables much faster spatial searches of the data by coordinate cuts.

Database Indices

In addition to the HTM, which is an overall indexing scheme for multidimensional spatial data, the DBMS itself has the capability to define indices for fast searches on each table. We have defined indices on all the major tables.

An index is a tree representation of a subset of the columns in a table that enables much faster searches of the table (compared to sequential scans of the table data) when constraints involving those columns are included in the query. All tables have an index on their primary key (unique row identifier), but the larger tables have indexes in addition to the primary key index. In all there are 3 kinds of indices:

• Primary Key Index - index on the unique primary key of a table.
• Foreign Key Index - index on a foreignkey of a table, i.e. a column that is a primary key of another table.
• Covering Index - an index that covers one or more columns of a table. This is a combined index on those fields, so it speeds up searches if any of those fields are included in the WHERE clause.

Click here to view a table of all the current indices defined on the data.