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 (115k points) | 90 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 (4.8k points) | 164 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) | 74 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) | 14 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 (420k points) | 2k views

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6

Ace Test Series: DBMS - Functional Dependency

asked Jan 21 in Databases by Na462 Loyal (6.8k points) | 51 views

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7

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) | 31 views

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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 (889 points) | 35 views

0 votes

1 answer

9

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) | 83 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) | 131 views

+1 vote

1 answer

11

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 (651 points) | 54 views

+1 vote

2 answers

12

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 (2.4k points) | 141 views

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MadeEasy Test Series: Databases - Functional Dependencies

asked Dec 19, 2018 in Databases by Vaishnavi01 (143 points) | 59 views

+1 vote

1 answer

14

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 (279 points) | 88 views

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1 answer

15

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 (751 points) | 180 views

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1 answer

16

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 Veteran (50.8k points) | 260 views

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17

#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) | 131 views

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18

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

asked Oct 31, 2018 in Databases by amit166 Junior (695 points) | 45 views

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2 answers

19

#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 (695 points) | 68 views

+2 votes

1 answer

20

Ace Test Series: DBMS - Canonical Cover In FD

asked Oct 29, 2018 in Databases by tusharforever (155 points) | 88 views

+1 vote

1 answer

21

#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 (4.8k points) | 70 views

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2 answers

22

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 (7k points) | 64 views

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23

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 (7k points) | 35 views

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24

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 (7k points) | 33 views

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25

Second Normal Form

asked Oct 21, 2018 in Databases by Na462 Loyal (6.8k points) | 147 views

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1 answer

26

Normalisation
Difference between composite and compound key??

asked Oct 5, 2018 in Databases by Raghav Khajuria Junior (723 points) | 61 views

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27

Normalization

asked Oct 4, 2018 in Databases by Vaishnavi01 (143 points) | 71 views

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2 answers

28

Lossless Decomposition and Dependency Preservation
Consider R(A,B,C,D,E)with the FD Set F(A->B, A->C, DE->C, DE->B, C->D) Consider this decomposition : R1(A,B,C), R2(B,C,D,E) and R3(A,E) Then, the decompositions is Lossless Decomposition Dependency Preserving Which of the ... 1 is TRUE but 2 is FALSE B) 1 is FALSE but 2 is TRUE C) Both 1 and 2 are TRUE D) Both 1 and 2 are FALSE

asked Sep 27, 2018 in Databases by Balaji Jegan Active (4.9k points) | 185 views

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29

Normalization - transitive dependency
In the books, it is written that a transitive dependency is one in which a non-key attribute is determining another non-key attribute. So, if ${R (A,B,C,D,E,F)}$ be a relation and ${ABC}$ ... about those dependencies in which the LHS is a combination of key and non-key attributes ? for example, what about ${ABD \to E}$ ?

asked Sep 15, 2018 in Databases by Harsh Kumar Active (1.2k points) | 78 views

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30

Testbook Test Series: Databases - Functional Dependencies
Consider a relation R(A,B,C,D,E,F,G) with set of functional dependencies F={AD->BF, CD->EGC, BD->F, E->D, F->C, D->F} The relation R is ... dependency preserving Decomposition is lossy and dependency preserving Decomposition is lossy and not dependency preserving Decomposition is lossless and not dependency preserving

asked Aug 21, 2018 in Databases by Mk Utkarsh Boss (35.1k points) | 104 views

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