Missing values in a relational data base
Nicolau Reinhard · DSpace@MIT (Massachusetts Institute of Technology) · 2011
Although missing (or null) values are found in most data bases they are not formally recognized by existing DBMS.The correct manipulation of those values is then left to the applications programs.This paper extends and formalizes a model suggested by Codd (4) for the explicit recognition of missing values by the relational algebra.It also explores the implications of the model and discusses useful applications.