Database Design and Relational Theory: Normal Forms and All That Jazz

© C. J. Date 2019

C. J. DateDatabase Design and Relational Theoryhttps://doi.org/10.1007/978-1-4842-5540-7_19

More on Consistency

C. J. Date¹ 

(1)

Healdsburg, California, USA

 

You may be consistent or inconsistent,but you shouldn’t switch all the time between the two.

—Anon., quoted in Edsger W. Dijkstra:

Selected Writings on Computing: A Personal Perspective (1982)

The following is a lightly edited extract from Appendix A:

• To say the database is consistent means it conforms to all stated constraints. Now, it’s crucially important that the database always be consistent in this formal sense; indeed, a database that’s not consistent in this sense, at some particular time, is like a logical system that contains a contradiction. Well, actually, that’s exactly ...