Arthur M. Keller. Set-Theoretic Problems of Null Completion in Relational Databases. Inf. Process. Lett., 22(5):261-265, 1986.
@article{Keller86:2, title = {Set-Theoretic Problems of Null Completion in Relational Databases}, author = {Arthur M. Keller}, year = {1986}, tags = {relational database}, researchr = {https://researchr.org/publication/Keller86%3A2}, cites = {0}, citedby = {0}, journal = {Inf. Process. Lett.}, volume = {22}, number = {5}, pages = {261-265}, }