Functional Dependency

What is Functional Dependency?

Definition and meaning of Functional Dependency

Functional dependency is a Relationship that exists while one Attribute uniquely determines every other attribute.

If R is a Relation with attributes X and Y, a functional dependency among the attributes is represented as X->Y, which specifies Y is functionally dependent on X. Here X is a determinant set and Y is a established attribute. Each price of X is related to precisely one Y fee.

Functional dependency in a Database serves as a Constraint between two sets of attributes. Defining practical dependency is an essential a part of Relational Database layout and contributes to factor Normalization.

What Does Functional Dependency Mean?

A useful dependency is trivial if Y is a subset of X. In a Table with the attributes of worker call and Social Security Range (SSN), employee name is functionally depending on SSN due to the fact the SSN is precise for individual names. An SSN identifies the employee particularly, but an employee call can not distinguish the SSN due to the fact a couple of employee may want to have the equal call.

Functional dependency defines Boyce-Codd Normal Form and 0.33 everyday Form. This preserves dependency among attributes, putting off the repetition of facts. Functional dependency is associated with a Candidate Key, which uniquely identifies a tuple and determines the fee of all other attributes in the relation. In some Instances, functionally based uNits are irreducible if:

• The proper-hand set of practical dependency holds most effective one attribute
• The left-hand set of practical dependency can't be decreased, on account that this can alternate the entire content material of the set
• Reducing any of the existing purposeful dependency might cHange the content material of the set

An crucial assets of a useful dependency is Armstrong’s axiom, that is utilized in Database normalization. In a relation, R, with 3 attributes (X, Y, Z) Armstrong’s axiom holds genuine if the subsequent situations are glad:

• Axiom of Transivity: If X->Y and Y->Z, then X->Z
• Axiom of Reflexivity (Subset Property): If Y is a subset of X, then X->Y
• Axiom of Augmentation: If X->Y, then XZ->YZ

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