Consider the schema R = (A, B, C, D, E, F) on which the following functional dependencies hold: A ➝ B B, C ➝ D E ➝ C D ➝ A
AEF, BEF and DEF
Required attributes: E and F never appear on a dependency’s right-hand side, so every key must contain both. Their closure is \((EF)^+=\{C,E,F\}\).
Complete the closure: Adding A yields B using A → B, then D using BC → D. Adding B yields D using BC → D, then A using D → A. Adding D yields A and then B. Hence AEF, BEF and DEF each determine all six attributes.
Minimality: Removing E or F loses an attribute that cannot be derived; removing A, B or D leaves EF, which is insufficient. Adding only C to EF adds nothing new, so these are exactly the three candidate keys.
Important Questions from Relational Model
Given the relational schema $R = (U,V,W, X, Y, Z)$ and the set of functional dependencies: $$\{U \rightarrow V, U \rightarrow W, WX \rightarrow Y, WX \rightarrow Z, V \rightarrow X\}$$ Which of the following functional dependencies can be derived from the above set?
- The ‘12 Rules for Relational Database’ were given by
- Which of the following statement(s) is/are FALSE in the context of Relational DBMS ?
I. Views in a database system are important because they help with access control by allowing users to see only a particular subset of the data in the database.
II. E-R diagrams are useful to logically model concepts.
III. An update anomaly is when it is not possible to store information unless some other, unrelated information is stored as well.
IV. SQL is a procedural language. - Let $R(A,B,C,D,E)$ be a relational schema with functional dependency set $F=\{A\rightarrow BC,\ CD\rightarrow E,\ E\rightarrow A\}$.
Which of the following statements is correct? Consider R (A,B,C,D,E) be relation with following dependencies:
C- >F, E- > A, EC- >D, A- >B. Which of the following is a key for R?
