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_11

11. Implicit Dependencies

C. J. Date¹ 

(1)

Healdsburg, California, USA

 

What are you implying?

—20th century catchphrase

We’ve seen several illustrations in previous chapters of the idea that certain dependencies imply others. To be specific, we saw in Chapter 7 how some FDs are implied by other FDs, and we saw in Chapters 9 and 10 how some JDs are implied by FDs. It’s time to take a closer look at such matters. Note that if we need to tell what normal form some given relvar is in, we do need to know all of the dependencies, implicit ones as well as explicit ones, that hold in that relvar. In this chapter, therefore, I plan to discuss among ...