What is the difference between a desirable and a undesirable

What is the difference between a desirable and a undesirable functional dependency? Describe the nature of the problems caused by undesirable functional dependencies,and What prevents us from simply ignoring undesirable functional dependencies?

Solution

Data redundancy and the modification consequences (insertion, deletion, and update) can be traced to “undesirable” functional dependencies in a relation schema

Desirable FD: is any FD in a relation schema, R where the determinant is a candidate key of R; this will not cause data redundancy.

Undesirable FD: is where the determinant of an FD in R is not a candidate key of R and this will cause data redundancy.

problems caused by undesirable FDs

1.reduundancy

2.data ambiguity

3. difficulty in acessing data and retrival

4.atomicity problems

5.data integrity problems

6.consistency problem

7.data islolation problems

8. durability problem

if we normalize data base it prevent us from ignoring underable Functional dependencies