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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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Functional Dependencies and Primary Keys

Question Does a Primary Key functionally determine every other attribute in the table? My thought Surely it has to doesn't it? Isn't that the point of primary keys?
user3211033
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Database Design - functional dependency methodology

Is there any standard methodology (step-by-step system) to determine the functional dependencies of a database? Maybe an algorithm that i could apply?I'm trying to optimize a beta database model i have created for a site like imdb and to work…
mankavvalos
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Functional dependencies for a relation with all prime attributes?

I am doing a database theory course as part of my CS degree, and we have to confirm a database we designed is in BCNF. I am trying to create the functional dependencies, but I don't know what to do when a relation is all prime. (All attributes are…
Fishingfon
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Second Normal Form; 2NF; why is not in 2NF

I have a following problem. I need to determine is the following assingment in the second normal form, and I have some problems understanding what the second normal form is, and how to determine it. I have this example for learning/practicing. R =…
depecheSoul
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Are b->d, d->b trivial functional dependencies?

by transitivity you can get b->b which is trivial (if I got this right), so are the other two also trivial? Studying functional dependencies and this appear in one of the exercises. Thanks,
hadroque
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detecting Losseless-join

Consider a database R = {Ra} with Ra = {A1, A2, A3, A4, A5, A6} and the dependencies F = {A1 → A2, A2 → A3, A3 → A4, A4 → A2, A3 → A5}. Consider R1 = {A1, A2}, R2 = {A2, A3, A4}, R3 = {A1, A2, A5}, R4 = {A3, A4}. How can I tell if R1,R2,R3,R4 is a…
Or Ami
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Finding functional dependency

How do I determine the functional dependency and the candidate key based on this case study? Course module and it can be performed by lecturer, student or visitor user. Course module consist of subject code and subject name. When admin creates…
Synetrix
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Writing the functional dependency

First module is User module. Administrators, students, lecturers or guests are users who benefit from the system and they take part in this module. Administrator will assign role as student or lecturer for each user. Each role has different…
Synetrix
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Determining the Normal Form without Functional Dependencies

If I am given the ER Diagram with the describing text, then I can simply write the corresponding relations. But how could the corresponding Normal Form be specified?
Luna28
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Find minimal candidate keys

I have 2 sets R = {A B C D} H = {AB-> C , AB-> D, D-> B} Want to find all minimal keys in R set My answer for minimal keys is : { A D } this is because AB -> C and AB -> D then AB -> CD since D -> B then AD is the minimal keys when i check my…
user3664490
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Can BCNF only be violated when table contains more than one candidate key?

I read in a book : "BCNF can be violated only when table contains more than one candidate key." Consider the following example: Sn Rollno Name Game 1 u11co098 Robert Basketball 2 u11ce034 Bob Cricket 3 u11co098 Robert …
Maverick
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Database Functional Dependency

I have the following table: I need to identify the functional dependencies in this table. BranchID(primary key) is unique and it is the same story with Address and Phone_number. I have an idea on what is but I need to double check to see if I am…
Softey
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How to find the candidate key by having a set of functional dependencies?

Consider relation R = (A, B, C, D, E, F) and a set of functional dependencies: AB --> C BC --> A BC --> D D --> E CF --> B What are all the candidate keys? Please if anyone can give me the answer and explain how.
user2974935
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Database candidate keys from functional dependencies - specific technicality

I am working with a relational database's set of attributes and set of functional dependencies and have a specific question about which keys would be considered candidate keys of this schema. The set of attributes I am working with is: R = (A, B, C,…
user1462294
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functional dependency

I am studying about functional dependency for sql and I got a question. We have functional dependencies A->B C->D CA->E D->F and I was trying to figure out whether that is decomposed relation or not For example we have two relationship First =…
Join Han
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