Contents
- 1 What is functional dependency preserving?
- 2 Does the decomposition preserve dependencies Why or why not?
- 3 What is closure set of functional dependency?
- 4 Is 4NF dependency preserving?
- 5 How to check if decomposition is dependency preserving?
- 6 Is the decomposition of FD1 a dependency preserving decomposition?
What is functional dependency preserving?
The dependency preservation decomposition is another property of decomposed relational database schema D in which each functional dependency X -> Y specified in F either appeared directly in one of the relation schemas Ri in the decomposed D or could be inferred from the dependencies that appear in some Ri.
How do you determine functional dependency?
To check whether an FD A->B can be derived from an FD set F,
- Find (A)+ using FD set F.
- If B is subset of (A)+, then A->B is true else not true.
Does the decomposition preserve dependencies Why or why not?
Note – Although a decomposition may be dependency-preserving it is not necessary that it is in a higher normal form.
What do you understand by dependency preservation?
Dependency Preserving In the dependency preservation, at least one decomposed table must satisfy every dependency. If a relation R is decomposed into relation R1 and R2, then the dependencies of R either must be a part of R1 or R2 or must be derivable from the combination of functional dependencies of R1 and R2.
What is closure set of functional dependency?
The Closure Of Functional Dependency means the complete set of all possible attributes that can be functionally derived from given functional dependency using the inference rules known as Armstrong’s Rules. If “F” is a functional dependency then closure of functional dependency can be denoted using “{F}+”.
How do you find functional dependencies examples?
A functional dependency is denoted by an arrow “→”. The functional dependency of X on Y is represented by X → Y. Let’s understand Functional Dependency in DBMS with example. In this example, if we know the value of Employee number, we can obtain Employee Name, city, salary, etc.
Is 4NF dependency preserving?
Clearly, testing that a decomposition is dependency preserving is difficult when multivalued dependencies are involved. Suffice it to say that the 4NF decomposition algorithm is not dependency preserving, and that some relation schemes and sets of dependencies do not have a dependency preserving decomposition into 4NF.
How to check whether a functional dependency hold in a relation R?
Functional dependency – For a given Left Hand Side (LHS) value of an attribute (or set of attributes) of a functional dependency, there should be at most one Right Hand Side (RHS) value of an attribute (or set of attributes). Then we would say that the functional dependency holds on that relation. REG_NO → STUDENT_NAME.
How to check if decomposition is dependency preserving?
Relation R is decomposed into R1 ( A, B, C) and R2 (C, D). Check whether decomposition is dependency preserving or not.
Which is closure of functional dependency FD of R?
FD+ -> Closure of set of functional dependency FD of R. With FD (FD1) R is decomposed or divided into R1 and with FD (FD2) into R2, then the possibility of three cases arise, FD1 ∪ FD2 = FD -> Decomposition is dependency preserving.
Is the decomposition of FD1 a dependency preserving decomposition?
But, there is no follow up in Functional Dependency S holds P (S –> P). FD1 U FD2 is a subset of FD. So as a consequence, given decomposition is not dependency preserving.