1. All values in a table column have the same data type. A value of a column in a row is the smallest unit of data that can be modified or selected from a table or to which functions can be applied.
2. All character strings in an alphanumeric column have the same length.
3. A numeric column is either a floating point column or a fixed point column. All numbers in a fixed point column have the same format; i.e., the same number of digits before and after the decimal point. All numbers in a floating point column have the same mantissa length.
4. Each column in a base table has a name that is unique within the table.