User-defined datatypes are built from the system datatypes and from the sysname user-defined datatype. After you create a user-defined datatype, you can use it to define columns, parameters, and variables. Objects that are created from user-defined datatypes inherit the rules, defaults, null type, and IDENTITY property of the user-defined datatype, as well as inheriting the defaults and null type of the system datatypes on which the user-defined datatype is based.