Essential vocabulary for using SQL with an ArcSDE geodatabase

The terms in this topic are defined based on their use with ArcSDE geodatabases, SQL, and spatial user-defined types. Some of the terms have different meanings outside the context of an ArcSDE geodatabase using spatial types.

Term	Definition
Coordinate system	A reference framework consisting of a set of points, lines, and/or surfaces and a set of rules, used to define the positions of points in space in either two or three dimensions. The Cartesian coordinate system and the geographic coordinate system used on the earth's surface are common examples of coordinate systems.
Layer	Once a spatial table is registered with ArcSDE, it is often referred to as a layer because registering a spatial table with ArcSDE adds a record to the LAYERS (or sde_layers) system table. Once a layer is registered with the geodatabase, it is called a feature class. This is not the same thing as a layer file (.lyr) or layers in the table of contents in ArcMap.
Multiversioned views	Multiversioned views incorporate database views, stored procedures, triggers, and functions to access a specified version of data in a geodatabase table using Structured Query Language (SQL).
ObjectID	The ObjectID field is maintained by ArcGIS and guarantees a unique ID for each row in the table. Most of the functionality in ArcGIS requires the ObjectID to be unique. If it is not unique, you will see inconsistent behavior in functionality. This field is also sometimes referred to as the row ID.
Register with ArcSDE	Registering a table with ArcSDE adds a record for the table to the TABLE_REGISTRY system table and one record for each column in the table to the COLUMN_REGISTRY system table. If the table contains a spatial column, a record for the table is added to the LAYERS system table and a record for the spatial column is added to the GEOMETRY_COLUMNS system table.
Register with the geodatabase	Registering a table or layer with the geodatabase adds a record for the table to the GDB_ITEMS system table and adds an ObjectID column to the table. This column is maintained and used by ArcGIS.
Spatial index	A spatial index is a database index created on the spatial column in a table to optimize access to the spatial data.
Spatial references	A spatial reference describes where features are located in the real world. You define a spatial reference when creating a geodatabase feature dataset or stand-alone feature class. The spatial reference includes a coordinate system for x-, y-, and z-values as well as tolerance and resolution values for x-, y-, z-, and m-values.
Spatial table	A spatial table is a table that includes one or more spatial columns. To create a spatial table, include a spatial column in the column clause of the CREATE TABLE statement.
ST_Geometry	The ST_Geometry data type is a user-defined data type (UDT) that allows you to define columns that store spatial data.
ST_Raster	ST_Raster is a user-defined data type. It is stored in a single row, in a single column of object type ST_Raster in a user-defined table. ST_Raster provides full geodatabase support as well as SQL access to raster data. This enables you to write SQL applications using your database management system (DBMS) that can access and use raster operations and queries.