This is the syntax of sp_addtype stored procedure:
sp_addtype [ @typename = ] type, [ @phystype = ] system_data_type [ , [ @nulltype = ] 'null_type' ] [ , [ @owner = ] 'owner_name' ]
where
typename - is the User-Defined datatype name.
phystype - is the SQL Server 2000 datatype, on which the User-Defined datatype is based.
nulltype - is the NULL or NOT NULL.
owner - is the owner of the User-Defined datatype.