Handling missing data by using stored truth values

Abstract

This paper proposes a method for handling inapplicable and unknown missing data. The method is based on: (1) storing default values (instead of null values) in place of missing data, (2) storing truth values that describe the logical status of the default values in corresponding fields of corresponding tables. Four valued logic is used so that the logical status of the default data values can be described as, not just true or false, but also as inapplicable or unknown. This method, in contrast to the “hidden byte” approach, has two important advantages: (1) Because the logical status of all data is represented explicitly in tables, all 4-valued operations can be handled via a 2-valued data manipulation language, such as SQL. Language extensions for handling missing data (e.g., “IS NULL”) are not necessary. (2) Because data fields always contain a default value (as opposed to a null value or mark), it is possible to do arithmetic across missing data and to interpret the logical status of the result by means of logical operations on the corresponding stored truth values.