Stack Overflow
Stack Overflow

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.

Enter image description here

544 questions
-1
votes
1 answer

SQL 3 NF normalization

I have a table with 4 columns to display the bill of buying an item, column 1 is the primary key, column 2 and 3 are the price and the amount of the item, column 4 is the sum of the price, which is calculated by multiply the value in column 2 and 3.…
YSJR
  • 1
  • 2
-1
votes
1 answer

Need example on functional dependency

Can i get example on functional dependency in database concepts with example? I understood that when a particular column is dependent on another column then it is called as functional dependent on other one.But i am not able to visulize with…
satheesh
  • 1,443
  • 7
  • 28
  • 41
-1
votes
1 answer

Derive an attribute as a superkey which is not even present in functional dependency

I got this question Consider The Following Relation R(A,B,C,D,E,G) And The Set Of Functional Dependencies F = { A → BCD BC → DE B → D D → A} Prove that AG is a superkey using Armstrong’s axioms. In the FD sets there is no…
Encipher
  • 1,370
  • 1
  • 14
  • 31
-1
votes
1 answer

A non prime attribute depends on composition of a partial Partial primary key and a non prime attribute. Is the table still considered to be in 3NF

Here is the table descriptions: Students SID SNAME 1 Adams 2 Jones 3 Smith 4 Baker Teachers TID TNAME 60192 Howser 45869 Langley Classes CID CNAME IS318 Database IS301 Java Student…
Shanmukha Reddy
  • 81
  • 1
  • 10
-1
votes
1 answer

functional dependencies , is this correct qusion

Consider relation R(A,B,C,D,E). The following functional dependencies are assumed to hold over R: A -> B, C B -> D What is a key of R? If there are multiple candidate keys list all. I think there is missing FD, but not sure can any one help and…
Maho
  • 3
  • 1
-1
votes
1 answer

Minimal cover FD

I have the following exercise text: Stack Overflow is a community where users (US), with a specific number of years of experience (Ye), can ask questions and give answers. Based on the given answers, each user earns a reputation (Re) and a badge…
Ele975
  • 352
  • 3
  • 13
-1
votes
1 answer

Is it possible to declare functional dependencies among non-primary keys in a single table?

Let's assume a functional dependency: R(A,B,C,D) & FDs{ A->B, A->C, (B,C)->D } A can identify any tuple. Defining A as a primary key, we can implement the dependency hold between A and others. But the combination of B & C can also uniquely identify…
Shamsul Arefin
  • 661
  • 7
  • 15
-1
votes
1 answer

find candidate key from functional dependency

I need help finding the candidate keys from the given relation: R (A,B,C,D,E) with FD: A -> BE B -> BE B -> D STEPS: I know all the attributes can identify themselves so: A,B,C,D,E -> {ABCDE} Now I know A -> BE, so i can cross out BE and get this:…
user372204
  • 69
  • 2
  • 10
-1
votes
1 answer

3NF Normalization and Decomposition

I am currently in a DB class and working through Normalization, and am running into some trouble. Am hoping I can get some assistance working through this. I have searched for the last 30 min and haven't found anything that helps solve my question,…
Tommy O'Connell
  • 71
  • 1
  • 1
  • 10
-1
votes
1 answer

Is A+B functionally dependent on C

I am currently studying Database Management and we were introduced to the idea of functional dependence: Let A and B be attributes in a relation. B is considered functionally dependent on A if and only if for every A value you can determine a B…
zai-turner
  • 75
  • 1
  • 10
-1
votes
1 answer

Prevent denormalization

I was wondering how to prevent denormalization in this case: Table Categories: - id - name Table Category_types: - id - name Association table: (category and category types are in a many-to-many relationship) - id - id_cat - id_cat_type I have…
Taz
  • 76
  • 1
  • 8
-1
votes
1 answer

Functional dependencies (first steps)

I'm practicing Functional Dependencies, i'm reading a book related to databases and they provided an example, it goes like this: A company performs all kinds of sales through different terminals (terminals for payment of debit and credit cards).…
JustToKnow
  • 785
  • 6
  • 23
-1
votes
1 answer

Database Normalisation based on functional dependency

What will be the decomposition for this relation in 1NF, 2NF, 3NF and BCNF Relation - Transfers(destination,departs,airline,gate,name,contact,pickup) Functional Dependencies - destination, departs, airline → gate gate → airline contact → name name,…
John Pollock
  • 11
  • 1
-1
votes
1 answer

Explanation of ER model to functional dependencies solution

I am trying to understand solution on one exercise that translates ER model to functional dependencies. As you can see above, we only have relation names and nothing else besides that, and by solution, they somehow come up to conclusion that …
GreatDuke
  • 214
  • 1
  • 10
-1
votes
2 answers

Functional Depedency with primary key and unique attribute

So imagine I have a relation like this: r(A, B, C, D, E) Where A is the primary key and C is unique. I'm having doubts on how the functional depedencies work, I know since A is the primary key every other attribute depends on it but I don't know…
MuchoG
  • 63
  • 5
1 2 3
…
36 37