Recent questions tagged functional-dependencies

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#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 in Databases by Rameesh (353 points) | 72 views

+1 vote

1 answer

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

asked Oct 28 in Databases by aditi19 Active (1.2k points) | 43 views

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3

DBMS: Multivalued Dependencies
Please solve the following question:

asked Oct 27 in Databases by chauhansunil20th Junior (801 points) | 22 views

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2 answers

4

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 in Databases by jatin khachane 1 Active (1.7k points) | 30 views

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5

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 in Databases by jatin khachane 1 Active (1.7k points) | 23 views

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6

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 in Databases by jatin khachane 1 Active (1.7k points) | 23 views

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7

Second Normal Form

asked Oct 21 in Databases by Na462 Loyal (6.9k points) | 107 views

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Normalisation
Difference between composite and compound key??

asked Oct 5 in Databases by Raghav Khajuria Junior (581 points) | 39 views

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9

Normalzation

asked Oct 4 in Databases by Vaishnavi01 (197 points) | 49 views

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10

Lossless Decomposition and Dependency Preservation

asked Sep 27 in Databases by Balaji Jegan Active (3.1k points) | 38 views

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11

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 ${ABC}$ is the only candidate key, then ${D \to ... 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 in Databases by Harsh Kumar Junior (803 points) | 22 views

+1 vote

1 answer

12

BCNF Decomposition

asked Jul 14 in Databases by Na462 Loyal (6.9k points) | 80 views

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13

Database Normal forms
Given a relation R(ABCD) with functional dependencies: $AB \to CD\\ BC \to D$ Normal form is? 1) 1 NF 2) 2 NF 3) 3 NF 4) BCNF

asked Jul 10 in Databases by cynicthnkr (157 points) | 72 views

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14

Normalization - 3NF doubt
A relation has the attributes R(ABCDEPG). The set of Functional Dependencies are : $F: { AB \to CD, DE \to P, C\to E, P\to C, B \to G }$ After normalising this relation till 3NF, I get the following tables : ${ ... A LOSSLESS AND DEPENDENCY PRESERVING PROPERTY IN 3NF - But I am not getting the Dependency Preservation property. Is something wrong with the decomposition ?

asked Jul 4 in Databases by Harsh Kumar Junior (803 points) | 101 views

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1 answer

15

Function Dependency question
Consider a relation R(A,B,C,D,E,F,H) with A as the only key. Assume that the dependencies E->F and C-> DEH hold.on R. 1. Is R in 2NF? If not, decompose to 2NF. 2. is R in 3NF? if not, decompose to 3NF. //What does " with A as the only key" mean ?

asked Jun 23 in Databases by karthikmenon (11 points) | 128 views

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16

Closure of a set of functional dependency

asked Jun 22 in Databases by Harsh Kumar Junior (803 points) | 102 views

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17

NORMALIZATION
Given: The Relation R(A,B,C,D,E) having (A,B) as Primary key. The set of functional dependencies: (A,C)-->D , (B,D)-->E. I want to Know whether the functional dependencies Given above are Partial FD's or Not?

asked Jun 8 in Databases by pradeepchaudhary Junior (759 points) | 124 views

+2 votes

1 answer

18

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 Loyal (6.9k points) | 96 views

+1 vote

1 answer

19

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 (975 points) | 84 views

+1 vote

1 answer

20

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 (8.3k points) | 83 views

+2 votes

1 answer

21

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) | 247 views

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22

#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 (8.3k points) | 155 views

+1 vote

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23

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 (23.7k points) | 115 views

+1 vote

1 answer

24

Functional Dependency
Validity of third statement

asked Dec 8, 2017 in Databases by Pawan Kumar 2 Active (4.6k points) | 46 views

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25

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 (16.2k points) | 180 views

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1 answer

26

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

asked Dec 1, 2017 in Databases by Harikesh Kumar Active (1.4k points) | 84 views

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27

Multivalued Dependency
Can anyone please explain it ?

asked Nov 30, 2017 in Databases by ankitgupta.1729 Loyal (8k points) | 91 views

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28

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

asked Nov 30, 2017 in Databases by ankitgupta.1729 Loyal (8k points) | 55 views

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29

Number of tables after decomposition

asked Nov 29, 2017 in Databases by Parshu gate Active (5k points) | 83 views

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30

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 (9k points) | 154 views

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