Recent questions tagged functional-dependencies

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1 answer

1

Dependency Preservation
Doubts : - 1. R(A,B,C,D) and The Functional Dependencies are = AB->C, C->AD . So when I'll decompose it then it will be R1(A,B,C) and R2(C,D).We cannot do R1(A,B,C) and R2(C,A,D) because the Production C->A will ... check R1 intersection R3 as well ? because if we do then it wont be lossless as there isn't any common attribute. Please tell the right way to check.

asked Apr 22 in Databases by Na462 Active (2.3k points) | 65 views

+1 vote

0 answers

2

3NF Normalization Doubt
Is a relation with multiple candidate keys in 3NF? According to this, As per the first definition any relation having multiple candidate keys will have transitive dependency to a non key attribute. My Inference : Since it has a Transitive dependency ... given is correct or not.And if it is correct can you please provide some other reference illustrating the same concept.

asked Jan 25 in Databases by Sourajit25 Junior (699 points) | 46 views

+1 vote

1 answer

3

FD cover
F: { A-> BC, B->C, AC->B } G: { AB->C, A->B, A->C } Does G cover F?

asked Jan 19 in Databases by Tuhin Dutta Loyal (7.8k points) | 59 views

+2 votes

1 answer

4

3NF Fully functional dependent
Consider the following statements: A relation R is in 3NF, if every non-prime attribute of R, is fully functionally dependent on some key of R. State True or False

asked Jan 15 in Databases by anabee (99 points) | 160 views

0 votes

0 answers

5

#candidate keys
Given a relation R{A, B, C, D, E, H} and having the following functional dependencies : {A → BC, CD → E, E → C, D → AEH, ABH → BD, DH → BC} The number of candidate keys for relation R is ________.

asked Dec 15, 2017 in Databases by Tuhin Dutta Loyal (7.8k points) | 93 views

+1 vote

0 answers

6

BCNF Normal form
R(A,B,C,D,E) AB ---> E CD ---->A B ------>C Decompose the following relation to BCNF and also state whether it is lossless and dependency preserving

asked Dec 12, 2017 in Databases by Mk Utkarsh Boss (12.3k points) | 89 views

+1 vote

1 answer

7

Functional Dependency
Validity of third statement

asked Dec 8, 2017 in Databases by Pawan Kumar 2 Active (4.4k points) | 38 views

0 votes

0 answers

8

Number of Super keys
Q1) Consider the relation with n attributes if any 2 attribute is a candidate key, then the total number of candidate keys are___ ? Then what will be the generalized formula I) $\sum_{i=2}^{n}C(n,i)$ II) $\sum_{i=2}^{n}C(n,i)*C(i,2)$ ... then ABE is a single superkey. So which one is correct? Q2) Is the answer remains same if use every in place of any in above question?

asked Dec 3, 2017 in Databases by Shubhanshu Boss (15k points) | 146 views

0 votes

1 answer

9

Dbms normalization
https://gateoverflow.in/?qa=blob&qa_blobid=11537552088967137608

asked Dec 1, 2017 in Databases by Harikesh Kumar Active (1.4k points) | 60 views

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0 answers

10

Multivalued Dependency
Can anyone please explain it ?

asked Nov 30, 2017 in Databases by ankitgupta.1729 Loyal (5.4k points) | 54 views

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0 answers

11

Multivalued Dependency
Can anyone please explain how to check Multivalued Dependency ?

asked Nov 30, 2017 in Databases by ankitgupta.1729 Loyal (5.4k points) | 49 views

0 votes

1 answer

12

Number of tables after decomposition

asked Nov 29, 2017 in Databases by Parshu gate Active (4.9k points) | 59 views

0 votes

0 answers

13

database normalisation
consider: T1: {A11, A12, A13} - key is A11 T2: {A21, A22, A11} - key is A21 T3: {A21, A23} - key is {A21 A23} T1, T2, T3 all are in which normal form? a) 2nf b) 3nf c) BCNF FUNCTIONAL DEPENDENCIES ARE NOT MENTIONED. SO, PLEASE EXPLAIN HOW TO CHECK NORMAL FORM FOR THE RELATION?

asked Nov 24, 2017 in Databases by iarnav Loyal (6.9k points) | 119 views

0 votes

2 answers

14

self doubt
relation schema with no non trivial fd's then relation is always in bcnf. please someone explain this i am not able to get it.

asked Nov 23, 2017 in Databases by arch Active (3.2k points) | 37 views

0 votes

1 answer

15

Match the following:
Match the following: List - I 1.Determinants 2.Candidate key 3.Non - redundancy 4.Functional dependency List - II A. No attribute can be added B. Uniquely identified a row C. A constraint between two attribute D. Group of attributes on the left hand side of arrow of ... 3 4 1 2 d) 4 3 2 1 Ans b) how Non - redundancy and Uniquely identified a row are related ? Thanks :)

asked Nov 20, 2017 in Databases by sunil sarode Active (1.1k points) | 101 views

0 votes

2 answers

16

2NF decomposition
How is it option D??

asked Nov 20, 2017 in Databases by Parshu gate Active (4.9k points) | 274 views

0 votes

0 answers

17

dbms question

asked Nov 19, 2017 in Databases by nikkey123 Active (1.5k points) | 90 views

+1 vote

2 answers

18

made easy test series
If a table $R$ has only one candidate key, then which of the following is always true? $R$ is in 2NF, but is not in 3NF If $R$ is in 3NF, it is also in BCNF $R$ is in 2NF, but may not be in 3NF None of these

asked Nov 10, 2017 in Databases by himanshu19 Junior (677 points) | 98 views

0 votes

1 answer

19

Please solve this Q
Question: 6 Given the following functional dependencies {X → W, X → Y, Y → Z, Z → PQ} Consider the FD set implied using above FD set. Implied FD set = {X → Z, X → WY, X → WZ, X → YQ, Y → P} The number of functional dependencies in implied FD set are invalid are _________.

asked Nov 10, 2017 in Databases by kallu singh Junior (773 points) | 90 views

+1 vote

1 answer

20

ugc net November 2017
Consider a Schema R(A,B,C,D) ad the following Functional Dependencies- A→B B→ C C→D D→B The decomposition of R into R1(A,B), R2(B,C), and R3(B,D) is Dependency preserving and lossless join. lossless join but not Dependency preserving. Dependency preserving but not lossless join. Not Dependency preserving and not lossless join.

asked Nov 8, 2017 in Databases by iarnav Loyal (6.9k points) | 228 views

0 votes

1 answer

21

Database doubt
Why B or B+ tree is prefer for database indexing rather than AVL tree ????

asked Oct 28, 2017 in Databases by air1ankit Active (3.2k points) | 48 views

+1 vote

1 answer

22

Doubt Database
How to remove extraneous attributes ?? Que - find the minimal cover of the functional dependency set A->BCDEF BC->ADEF B->F D->E explain whlole procedure please

asked Oct 27, 2017 in Databases by air1ankit Active (3.2k points) | 88 views

+1 vote

2 answers

23

Dbms #self doubt
1. How many super key is possible if (a,bc,cd) is candidate key and R(ABCDEF) #DOUBT When we use veen digram why we are taking only intersections part only ??? Need help please explain ..

asked Oct 26, 2017 in Databases by air1ankit Active (3.2k points) | 115 views

0 votes

1 answer

24

partial dependency

asked Oct 25, 2017 in Databases by set2018 Loyal (7.6k points) | 65 views

0 votes

1 answer

25

Functional Dependency
Consider the relation R(A,B,C) and functional dependencies F={A->B, B->C} then what are the number of functional dependencies in $F^{+}$ ?

asked Oct 24, 2017 in Databases by Shweta Nair Junior (615 points) | 56 views

+3 votes

1 answer

26

Doubt Database
What is difference between attributes set of cross product and attributes set of joine ???

asked Oct 23, 2017 in Databases by air1ankit Active (3.2k points) | 86 views

+1 vote

1 answer

27

Doubt database
What is basic difference between mandatory attributes and multivalued attributes???

asked Oct 19, 2017 in Databases by air1ankit Active (3.2k points) | 64 views

0 votes

1 answer

28

Database
1- R(ABCD) FD'S ARE {AB->C ,C->D,D->EA ,DE->F,EF->B} 2-R(ABCD) FDS ARE { A->BC, CD->E, B->D,E-A} 3- R(ABCD) {AB-> CD,C->B,D->C} Find the candidate key ??? For above questions and please explain too.

asked Oct 17, 2017 in Databases by air1ankit Active (3.2k points) | 72 views

+1 vote

1 answer

29

Database management
Que- R(ABCD) and fds are { A->B ,B->C,C->A} then number of candidate key is........? Explain please

asked Oct 17, 2017 in Databases by air1ankit Active (3.2k points) | 41 views

+1 vote

1 answer

30

DBMS #DOUBT ...
correct???

asked Oct 17, 2017 in Databases by air1ankit Active (3.2k points) | 39 views

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