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Questions tagged [functional-dependencies]

A functional dependency is a constraint between two sets of attributes in a relation, in relational algebra, databases and type systems.

Functional dependencies (FD) are fundamental to the process of normalization.

Given a relation R, a set of attributes X in R is said to functionally determine a set of attributes Y, also in R, (written X → Y) if, and only if, whenever two tuples coincide on all attributes of X, they also coincide on all attributes of Y. Sound, complete and non-redundant axiomatisation of functional dependencies is given by Armstrong rules. Functional dependencies are also used in the Haskell programming language to describe relations between types, to support type level relational programming.

In other words, a dependency FD: X → Y means that the values of Y are determined by the values of X. Two tuples sharing the same values of X will necessarily have the same values of Y.

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What determinants do I have in my entity? Trying to understand BCNF

My teacher told me that if an entity is in BCNF all determinants should be a super key, but i'm struggling to understand this. I have an entity for a cinema database with following attributes: Showtime_id (PK), Date, Showtime, Hall. I understand…
sakura
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How do deal with combined entity types when computing the closure of a set of attributes

I'm revising for coming exams, and I am having trouble understanding an example question regarding the closure of attributes. Here is the problem: AB→C BE→I E→C CI→D Find the closure of the set of attributes BE, explaining each step. I've found…
grainman
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Dependency preservation, based of original functional dependencies or canonical cover?

Given these functional dependencies for R: {A,B,C,D,E,F} AC->EF E->CD C->ADEF BDF->ACD I got this as the canonical cover: E->C C->ADEF BF->C And then broke it down to Boyce Codd Normal Form: Relation 1: {C,A,D,E,F} Relation 2: {B,F,C} I…
Loqgar
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Normalization generates a table with no clear purpose

Overview I have an assignment regarding database modelling in which I have to model a database for a shop. When normalizing from 0NF to 3NF, I end up with a table whose attributes do not seem to be related. NOTE For brevity, I removed most of the…
Isfaaq
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Is this in BCNF?

Assume that the relation is obtained through decomposition from a relation with attributes ABCDEFGHI and that dependencies over ABCDEFGHI are listed below. R(A,B,F) B->E A->F We need to convert this relation into BCNF What i have done till now…
sania00
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Dependency Preserving Decomposition with a functional dependency doesn't appear in the sub-schema

I'm reading a textbook containing the following question: Given the following relation R {A,B,C,D,E,H} and the functional dependencies AB->CD, BC->D, C->H, D->HB, CH->AE does the following decomposition is dependency preserving? R1(A,C,E,H)…
DsCpp
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Can an attribute that only appears on the RHS of a Functional Dependency be a prime attribute?

I am working on a normalization problem and am hung up on whether the given relation is in 2NF form. The relation is given as R(A,B,C,D,E,F,G) and the set of FD's is given as: { A->B, B->AC, F->ACDE, ADE->FG }. The candidate keys that I have found…
WRK
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Determining Candidate Keys from Functional Dependencies

If I Have R(E, F, G, H), what would be the candidate keys from these functional dependencies? FD1: EF -> G FD2: EF -> H FD3: G -> E FD4: H -> F My thought process was that EF would be considered a candidate key, since EF -> G and EF…
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Functional dependency inferences with redundant attribute

Given 1) CA -> B and 2) B -> C can you infer A -> B using Armstrong's axioms? I tried to use inference rules to prove this, but get stuck. BA -> CA Augmentation of A BA -> CA and CA -> B Transitive property AB -> B It seems to makes sense to be…
Henry
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What are the likely FDs(Functional Dependencies) for this relation?

ABC(doc-firstname, doc-surname, doc-gender, doc-rego, doc-qualification, pat-ID, pat-givename, pat-surname, pat-gender, pat-DOB, pat-addr, pat-phone, app-ID, app-datetime, app-type) ● A doctor has a unique registration number (doc-rego) and is also…
user24529
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BCNF - Is it possible here? Name, Sport Centre, Sport

I'm trying to get a better understanding of normalisation so I can use best practices going forward. I've found a question in an old book and I'm a little confused by it. Essentially I'm given this table with the following data: Name Sport …
JamMan9
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Try to find Partial and transitive dependencies

Cust_id| Name |Ord_no|Ord_Date |PROD-ID|Descr |Qty_ord| C001 | Pink | O81 | 15-Apr |P005 |Chisel|6 | C001 | Pink | O81 | 15-Apr |P004 |Jane |14 | C0075 | Red | O99 | 16-Apr |P015 |Saw |3 | C009 |…
Rohan Kapoor
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Deriving functional dependencies of minimal cover

Given the set of dependencies AB->C, BD->EF, AD->GH, A->I, H->J. How would you find a minimal cover? By applying a process described in a book I get: AB->C, A->I, BD->EF, AD->GH, H->J instead of AB->CI, BD->EF, AD->GHIJ. Is it possible to combine…
Drimades Boy
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How to check if two sets of functional dependencies are equivalent?

FD1={A->DF, A->B, D->F, DE->F} , FD2={A->BD, D->EF} from FD1 : A->DF turns into A->D and A->F . Also A->F is not needed cause we can get there with A->D and D->F . So A->BD ,because A->B and A->D How to prove that D->EF in FD1?
Mitsos
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database - functional dependencies

given a relational schema R(A,B,C,D,E,G) with the set of functional dependencies: F = {A->BC,C->BG,CD->E,G->D,E->B,CE->A,BH->E} Can anyone explain to me how to find the relation between C and E? And between C and A?
Ghada
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