Recent questions tagged functional-dependencies

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Made Easy Test Series:DBMS-Functional Dependency
Consider a relation $R\left ( A,B,C,D,E \right )$ and functional dependencies are $F=\left \{ AC\rightarrow B,C\rightarrow D,A\rightarrow E,C\rightarrow B \right \}$ Relation $R$ ... Then Is it a lossless decomposition? I am getting doubt, how it can be not lossless decomposition?

asked Apr 28 in Databases by srestha Veteran (113k points) | 77 views

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2 answers

2

Molina Exercise-3.3 BCNF decomposition
Decompose into BCNF R(A, B, C, D, E) FD: AB->C, C->D, D>B, D->E

asked Apr 14 in Databases by aditi19 Active (4.1k points) | 136 views

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1 answer

3

made easy test series - lossless join and dependency preserving
How is A answer?

asked Apr 7 in Databases by amitqy Active (1.8k points) | 65 views

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4

Doubt
Do we need to find closure of functional dependencies of original relation to check whether the decomposed tables are in 2NF . I know that we have to do the above process for 3NF and BCNF . If yes , please give a example where we need to do it

asked Mar 30 in Databases by ashunimbz (59 points) | 13 views

+2 votes

1 answer

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GATE2019-32
Let the set of functional dependencies $F=\{QR \rightarrow S, \: R \rightarrow P, \: S \rightarrow Q \}$ hold on a relation schema $X=(PQRS)$. $X$ is not in BCNF. Suppose $X$ is decomposed into two schemas $Y$ and $Z$, where $Y=(PR)$ ... $Y$ and $Z$ is dependency preserving and lossless Which of the above statements is/are correct? Both I and II I only II only Neither I nor II

asked Feb 7 in Databases by Arjun Veteran (416k points) | 1.9k views

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Ace Test Series: DBMS - Functional Dependency

asked Jan 21 in Databases by Na462 Loyal (6.7k points) | 46 views

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self doubt - NO. of tables after normalizing
Are 3NF decompostions and BCNF decompostions unique? Are 4NF important for GATE (since I've left them :( ) See, I am asking this question because I want to know whether they'll ask about no. of tables we get after normalizing upto 3nf or bcnf. Now ... I am in a bit hurry to search for that.. so please forgive me if it has been already asked.) Thank you.

asked Jan 21 in Databases by Harsh Kumar Active (1.2k points) | 28 views

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1 answer

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GATEBOOK-2019 Mock Test1-55
Consider the relation schema $R(A, B, C, D)$ with functional dependencies $A\to B, BC\to A$ and $B\to D,$ which is the minimum cover itself. The number of candidate key(s) of $R$ is ______

asked Jan 19 in Databases by GATEBOOK Boss (11.4k points) | 78 views

+2 votes

2 answers

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GATEBOOK-2019 Grand Test DBMS-3
Suppose we are told that $R(A,B,C,D)$ is in $BCNF$, and that three out of the four functional dependencies $(A)-(D)$ listed below hold for $R$. Choose the Functional dependency that need not be there on $R$? $A \to BCD$ $BC \to A$ $CD \to B$ $D \to C$

asked Jan 6 in Databases by GATEBOOK Boss (11.4k points) | 143 views

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1 answer

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GATEBOOK-2019 Grand Test DBMS-21
Consider the following table $R(A,B,C,D)$ and functional dependency set $F=\{A\to BD, BC\to D, CD\to A\}.$ $R$ is decomposed into $R_1(A,B,C), R_2(C,D,A)$. The highest normal form satisfied by the decomposition $(R_1,R_2)$ is? $3NF$ $BCNF$ $2NF$ $1NF$

asked Jan 6 in Databases by GATEBOOK Boss (11.4k points) | 111 views

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11

Self-doubt | DBMS | Functional Dependency
Can someone explain the paragraph marked based on relation $r$ given in Figure 7.2? Reference: Database System Concepts by Silberschatz, Korth, Sudarshan 4th Edition.

asked Jan 5 in Databases by zeeshanmohnavi Junior (855 points) | 33 views

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12

MadeEasy Test Series: Databases - Functional Dependencies
Consider the following relation R(A, B, C, D, E, F, G) and set of functional dependencies. F={BCD → A, BC → E, A → F, F → G, A→G, C → D} Which of the following is minimal cover of F? (A) {BC → A, BC → E, A → F, C → D, A → G} (B) ... → D} (D) {BC → A, BC → E, A → F, C → D} My doubt here is Since (B) covers F, why can't it be a minimal cover?

asked Jan 5 in Databases by Shivam Kasat Active (3.1k points) | 75 views

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Sel doubt
Relation R (A,B,C,D,E,F) Functional dependency: ABC -->DEF, BC-->EF, EF-->D. Decomposition: R1 (ABCDF), R2 (BCDE). Is this decomposition lossy? Is this decomposition preserve functional dependency? Plz explain how to check functional dependency is preserved or not in decomposition.

asked Dec 24, 2018 in Databases by Raj Kumar 7 Active (1.1k points) | 125 views

+1 vote

1 answer

14

ME test series
Consider relation R(A,B,C,D,E,F,G) with the following functional dependencies AB$\rightarrow$CD , D$\rightarrow$B, AF$\rightarrow$D, DE$\rightarrow$F, C$\rightarrow$G, F$\rightarrow$E, G$\rightarrow$A. What is the highest normal form.

asked Dec 20, 2018 in Databases by Rajat Agrawal007 Junior (641 points) | 53 views

+1 vote

2 answers

15

MadeEasy Test Series: Databases - Functional Dependencies
Consider Relation R(A,B,C,D,E,F,G) and set of Functional dependencies: F = {BCD → A, BC→ E, A→ F, F→ G, C→ D, A→ G} What is the minimal cover of F ? Answer given: BC → A, BC→ E, A→ F, F→ G, C→ D Why the answer cant be: BC → A, BC→ E, A→ F, C→ D, A→ G

asked Dec 20, 2018 in Databases by Shamim Ahmed Active (2.3k points) | 123 views

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16

MadeEasy Test Series: Databases - Functional Dependencies

asked Dec 19, 2018 in Databases by Vaishnavi01 (143 points) | 56 views

+1 vote

1 answer

17

Self doubt dbms Normalisation
Is minimal set of functional dependency for a functional dependency set is always unique???

asked Dec 10, 2018 in Databases by gatecrack (243 points) | 83 views

+2 votes

1 answer

18

MadeEasy Test Series: Databases - Functional Dependencies
Consider the relation R(A,B,C,D,E) with the functional dependencies : A → B, B → C, C → A, D → E, and E → D The Maximum possible super-keys of R is ______________?

asked Dec 7, 2018 in Databases by naveen bhatt Junior (737 points) | 176 views

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1 answer

19

Functional preserving
Given $R(A,B,C,D,E)$ and $F:\left \{A\rightarrow BC ,CD\rightarrow E,B\rightarrow D,E\rightarrow A\right \}$,Decompose into $BCNF?$ $(a)$Every $BCNF$ is $3NF$ and vice versa $?$ $(b)FD$ preserving or not$?$ $(c)$ Lossless decomposition or lossy decomposition?

asked Nov 20, 2018 in Databases by Lakshman Patel RJIT Boss (45.8k points) | 246 views

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20

#Self Doubt
In definition of transitive dependency we use conditions as A → B It is not the case that B → A B → C I am not able to understand why we need condition 2 for this ?

asked Nov 6, 2018 in Databases by Rameesh (435 points) | 128 views

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21

MadeEasy Workbook: Databases - Functional Dependencies
F={AB->C,A->B} FIND EXTRANEOUS ATTRIBUTE ??

asked Oct 31, 2018 in Databases by amit166 Junior (555 points) | 44 views

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2 answers

22

#madenotes
A B C 1 1 1 1 1 0 2 3 2 2 3 2 FIND NON-TRIVIAL DEPENDENCY

asked Oct 31, 2018 in Databases by amit166 Junior (555 points) | 67 views

+2 votes

1 answer

23

Ace Test Series: DBMS - Canonical Cover In FD

asked Oct 29, 2018 in Databases by tusharforever (145 points) | 81 views

+1 vote

1 answer

24

#Functional Depencency
max number of FD in a relation with 'n' attributes=$2^{2n}$ how this formula is obtained?

asked Oct 28, 2018 in Databases by aditi19 Active (4.1k points) | 68 views

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25

Self Doubt
A relation R is in 2NF if every non-prime attribute of R is fully functionally dependent on every key of R true or false R(A,B,C) F {A->B,B->C} Here key = A R is in 2NF So is C is fully functional dependent on every key here ?. It is not dependent on key infact ?

asked Oct 24, 2018 in Databases by jatin khachane 1 Loyal (6.8k points) | 62 views

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26

Self Doubt
While checking for normal forms Why we only check conditions only on F not on F+ eg R(A,B,C) F = {A->B , B->C} is in 3NF or not ? We will apply defination of 3NF i,e either LHS should be super key or RHS should be prime attribute ON ... if decomposed relation is in particular normal form we apply check on ALL IMPLIED FDs from F ?? In below ex should all implied FDs be checked ??

asked Oct 23, 2018 in Databases by jatin khachane 1 Loyal (6.8k points) | 33 views

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27

Self doubt
Can Prime attribute be NULL in any of the the Candidate key ?? Can Prime attribute be NULL in Primary key ??

asked Oct 23, 2018 in Databases by jatin khachane 1 Loyal (6.8k points) | 32 views

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