A Relativity representation of a domain. A custom data type, which is defined by the user, is a named set of properties for a column, including its ODBC data type, length, default value, whether the column allows null values, whether the column is constrained to certain values, and, for numeric type columns, the precision and scale. After a custom data type is defined, it can be used in place of ODBC data types in column definitions, thus giving all columns with the same user data type similar characteristics.