What are the conditions for a functional dependency to exist? Let be a relation R of scheme: R(A,B,C,D,E) and r an instance of the relation. What functional dependencies verify r?



Observing the functional dependencies that r verify are  doesn't show that they exists on R and are verified by all possible instances of R.

The definition of a functional dependency is:



I said that there is:

A→E, C→A, B→E, C→D, C→E, D→E, C → A, C→B

AB→D, AB→E, AC→B, AD→D, AD→E, BC→A, BC→D, BC→E, BD→ A, BD→C, BD→E, DE→A, DE→ C

ABC→D, ABC→ E, ABD→E, ABE→D

But I don't know if they do exist, I don't know what to do to verify if they actually exists
Community Wiki answer generated from comments on the question by Renzo and ypercubeᵀᴹ



The definition of functional dependencies requires that they must hold for every possible instance.

From an instance, you cannot find the functional dependencies that hold in a certain relation schema.

You also missed A → D.