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
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Lifting an instance of an element to a type-level list instance with functionnal dependencies
Let's suppose I have a Coproduct data type whose constructor has kind Coproduct :: [*] -> * . I also have a class
class MyFun s x | x -> s where
myFun :: s -> x
Whenever I have a list of ...
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attribute partially depends on a candidate key but the answer says the relation is in 3NF
The relation R(ABCD) has the following non-trivial FDs that hold:
{ A -> B ; B -> A ; A -> D ; D -> B }
What is the highest normal form of R?
Since A -> B is extraneous, I removed it ...
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1
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96
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Dependency-Preserving Decomposition
Given the schema R = (A, B, C, D, E, H, I) with the functional dependency set
F = {A→B, C→D, CD→E, BD→AH, H→D, AC→H}:
Is the decomposition of R into (A, B, C, D, I) and (B, C, E, H) dependency ...
-1
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1
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Is this BCNF? If not, what is a decomposition and is it FD preserving?
Consider relation schema R = (A, B, C, D, E) with functional dependencies BCE -> D, BDE -> C, ABE -> D and AB -> C.
Is the relation schema in BCNF? If not: What is a BCNF decomposition? Is ...
0
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1
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181
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Database Normalization BCNF decomposition
I have a relation schema M with the attributes {B, C, D, E, R} and the following set of functional dependencies:
B, D, E -> R
B, D, R -> E
B, C, D -> R
C, D -> E
I want to perform a BCNF ...
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2
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1
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68
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Make Haskell type system understand that fundeps carries over a composite (tuple-like) type
I have the following code, which I use to convert a HList-of-touples (or more like, tree-of -touples) into the same shape, but instead of a tuple, just keeping the second element.
The problem is, this ...
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How does this relation produce candidate keys?
Given relation
R(a,b,c)
and that there are no functional dependencies:
How are candidate keys computed?
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SELECT Unaggregated Variables, Functionally Dependent on GROUPing Variables
Background
I am working in a very restricted T-SQL environment, where one may only define the "body" of a VIEW: presumably the ... in
CREATE VIEW My_View AS ...
under the hood. Here is my @...
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Struggling with functional dependency practice questions
I'm going over some practice questions.
F={ B→E, C→B, CD→E, ABE→C}
I tried to make a canonical cover -
Fc ={ B→E, C→B, D→E, AB→C}
Then finding candidate keys -
ADB, ADC
Is R in BCNF? I thought it ...
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Is this allowed in BCNF Normalization?
I know that in BCNF if A->B then A must be a candidate key. But what about if A is part of the candidate key but not the whole candidate key?
Let me explain in an example:
Exercise 1:
Candidate ...
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1
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Definition of functional dependency, ambigiuous "for all pairs"
for all pairs of tuples t1 and t2 such that
t1[A] = t2[A] then t1[B] = t2[B]
Can "a pair" also be a pair of the same tuple, meaning t1 = t2, or does it mean only two distinct tuples?
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Decomposing tables where some attributes aren't in any minimal, non-trivial functional dependency
While writing a library to automatically decompose a given table, I came across some special cases where the first steps of Bernstein's synthesis for 3NF (ACM 1976) give me results I don't expect.
...
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0
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Data normalisation into third normal form
I have done data normalization on dummy data and would like to know if I did it correctly. If it is done correctly, I would also like to ask two things below, because it is about 3NF.
1NF: This table ...
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Error matching types: using MultiParamTypeClasses and FunctionalDependencies to define heterogeneous lists and a function that returns first element
There is a relevant question concerning Functional Dependencies used with GADTs. It turns out that the problem is not using those two together, since similar problems arise without the use of GADTs. ...
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Definition for relation to be in 3NF using canonical cover
We are using following definition of 3NF:
A schema R is in third normal form (3NF) if for all FD α → β in F
+, at least one of the following holds:
α → β is trivial (i.e., β ⊆ α).
α is a superkey ...
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