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Questions tagged [functional-dependencies]

10 questions
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"Functional dependencies" with cardinality constraints

Let us write $\{ A_1, \ldots, A_k\} \rightrightarrows^n \{B_1, \ldots, B_m\}$ for a relation $R$ if for all $\langle a_1, \ldots, a_k\rangle$ we have $\left\lvert \pi_{B_1, \ldots, B_m} \sigma_{\bigwedge_{i = 1}^k A_i = a_i} R\right\rvert \le n$…
Kristóf Marussy
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Is there a functional programming language with inherent change propagation?

Change propagation in programming environments is an add-on at the framework level such as React. There was a lot of work on dataflow virtual machines in the wake of Backus's Turing Award Lecture on formal functional programming. This is because…
James Bowery
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Functional dependencies on relational schema

Given a relational schema $R(V,W,X,Y,Z)$ with functional dependencies $F = \{VW \to X, X \to YZ, W \to VX, V \to W, Z \to XY\}$. What are the keys of $R$? Is the key just $V$? If so, is $\{ R_2(V,W,Z), R_3(V,X,Y) \}$ the lossless-join decomposition…
paradoxica
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Database Theory - Does the dependency preservation and lossless join properties hold for every decomposition of a relation into 3NF?

Database Systems, 6th ed by Ramez Elmasri and Shamkant Navathe Chapter 15, section 15.2 Properties of Relational Decompositions: Claim 1. It is always possible to find a dependency-preserving decomposition $D$ with respect to $F$ [$F$ is the set of…
Ebin J
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Relation is in 2NF or not?

Consider a relation R(A,B,C,D,E) and the only FDs, ABD->C BC->D CD->E These are the only 3 FDs. I want to know if the above relation is in 2NF or not. According to the definition of 2NF, a relation to be in 2NF, it should be in 1NF and it should not…
user9544852
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Find number of candidate keys given non-trivial functional dependency X->Y, where X is some set of attributes and Y is some prime attribute

In a relation R, if X is some set of attributes and Y is some prime attribute such that X uniquely determines Y is a non-trivial FD. Then is it true that R has at least two candidate keys? For instance, take the relation schema R(Class_Id,…
Haslo Vardos
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Functional dependencies , minimizing SUU->V

Can SUU->V or any functional dependency that contains two or more times each attribute be simplified to the same dependency with one attribute? So SUU->V becomes SU->V or STTT->Q becomes ST->Q ?
user102382
0
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Normal form after decomposition of a relation

I came across a text recently which claims that if we perform a lossless decomposition of a relation R into smaller relations R1 and R2, and if R is in 3NF, both R1 and R2 are 3NF. I felt a bit suspicious regarding this claim, but couldn't find…
Abhilash Mishra
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Functional Dependencies

Let relational schema R(A,B,C,D,E,F,G,H,I). The functional dependencies are: A -> BC, AD -> BE, C ->F , A->F , D-> E Find the number of non-trivial functional dependencies ? I know that R has only five non-trivial functional dependencies but i do…
Emily Serone
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Given a relation and asked to enumerate all FD's and mark the trivial FD's

Given a relation R(A,B,C) and a FD set (A->B, B->C), find the FD Closure. Enumerate all the FD's and organize them accordingly to the LHS of the FD's. Mark all the trivial FD's. I am a little confused with the second part of the question and don't…
Jerrico Kyle
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