Functional Dependency Set Closure (F+) Functional Dependency Set Closure of F is the set of all functional dependencies that are determined by it. Example of Functional Dependency Set Closure : Consider a relation R(ABC) having following functional dependencies : F = { A → B, B → C } To find the Functional Dependency Set closure of…

# Functional Dependency

Minimal Sets of Functional Dependencies or Irreducible Set of Functional Dependencies or Removal of Extraneous Attributes or Canonical Cover – Some Terms Before Making a Move to the Minimal Sets of Functional Dependencies /Canonical Cover – Non Redundant Functional Dependency – A set F of FDs is non redundant, if there is no proper subset F’of…

Questions on Minimal Cover or Irreducible Sets or Canonical Cover – Question 1 :Find the minimal cover or irreducible set from the following functional dependencies : AB → CD BC → D Solution : Step 1 : Union Simplification : AB → C ..(1) AB → D ..(2) BC → D ..(3) Step 2 :…

Equivalence of Sets of Functional Dependencies Example – Let F & G are two functional dependency sets. These two sets F & G are equivalent if E+=F+. Equivalence means that every functional dependency in F can be inferred from G, and every functional dependency in G an be inferred from F. → F and G are…

Membership Test for Functional Dependency or Identification of additional Functional Dependencies by Closure Set – What is the Membership Test for Functional Dependency ?? Let F be the Functional Dependency set. X → Y be any non trivial functional dependency. X → Y implied in Functional Dependency Set only if X+ determines Y. Method : To determine,…

How to Find Candidate Key using Functional Dependencies – In the previous post (How to Find Super Key from Functional Dependencies), we identify all the superkeys using functional dependencies. To identify Candidate Key, Let R be the relational schema, and X be the set of attributes over R. X+ determine all the attributes of R, and therefore X…

How to Find Super Key From Functional Dependencies Let R be the relational schema, and X be the set of attributes over R. If X+ determine all the attributes of R, then X is said to be superkey of R. To Identify Super keys, we need to follow some steps – Compute Closure for the attributes of combination…

Prime and Non Prime Attributes in DBMS with Example – Prime Attributes – Attribute set that belongs to any candidate key are called Prime Attributes. (union of all the candidate key attribute) {CK1 ∪ CK2 ∪ CK3 ∪ ……} If Prime attribute determined by other attribute set, then more than one candidate key is possible….

Questions on Super Keys and Candidate Keys using Closure Identify Super Keys and Candidate keys : Question 1 : Let R(ABCDE) is a relational schema, where (AB)+ = ABCDE (A)+ = ABCDE Is AB: Candidate Key or Not?? Solution : AB : Not a Candidate Key, AB is only : Super Key Question 2 :…

Closure of Functional Dependency Example and Applications of Closure – Closure of a set (X+) is the set of attributes functionally determined by X. Let S be the set of functional dependencies on relation R. Let X is set of attributes that appear on left hand side of some FD in S and we want to determine… |