In using extended properties, you can add text, such as descriptive or instructional content, add input masks, and add formatting rules as properties of objects in a database or of the database itself.
Level 0 is the highest level and is defined as objects that are contained at the database scope.Level 1 objects are contained in a schema or user scope, and level 2 objects are contained by level 1 objects.Extended properties can be defined for objects at any one of these levels.References to an object in one level must be qualified with the names of the higher-level objects that own or contain them.For example, when you add an extended property to a table column, level 2, you must also specify the table name, level 1, that contains the column, and the schema, level 0, which contains the table.
In the following example, the extended property value USE Adventure Works2008R2; GO EXEC sys.sp_addextendedproperty @name = N'MS_Description Example', @value = N'Minimum inventory quantity.', @level0type = N'SCHEMA', @level0name = Production, @level1type = N'TABLE', @level1name = Product, @level2type = N'COLUMN', @level2name = Safety Stock Level; GO The following tables list objects to which you can add extended properties.Their valid level 0, level 1, and level 2 object types are listed and also the permissions required to add, drop, or view the extended properties.Extended properties can be used for the following: Extended properties should not be used to hide sensitive information about an object.Any user who has been granted permission on the object will be able to view the extended properties on that object.For example, if you grant a user SELECT permission on a table, the user will be able to view the extended properties on that table. Multiple extended properties can be added to a single object.For specifying extended properties, the objects in a SQL Server database are classified into three levels, 0, 1, and 2.