functional dependencies and normal form

Question 1

what is a functional dependency

Answer 1

when x implies y, if x agrees then so does y making it redundant as they’re both essentially the same

Question 2

decomposition

Answer 2

removing dependencies and anomalies then putting them in their own table

Question 3

deletion anomaly

Answer 3

when deleting a record causes something that you didnt mean to to be deleted

Question 4

insertion/modification anomaly

Answer 4

cannot insert new data due to other required data missing

Question 5

what is f+ closure (Armstrong’s axioms) used for

Answer 5

to analyse functional dependencies and reveal hidden dependencies

Question 6

what are the 5 armstrongs axioms

Answer 6

reflexivity
augmentation
transitivity
union
decomposition

Question 7

reflexivity

Answer 7

if x ∈ y then y -> x

Question 8

augmentation

Answer 8

if x -> y then yz -> z for any z

Question 9

transitivity

Answer 9

if x -> y and y -> z then x -> z

Question 10

union

Answer 10

if x -> y and x-> z then x -> yz

Question 11

decomposition

Answer 11

if x -> yz then x -> y and x-> z

Question 12

what is first normal form

Answer 12

only atomic values

Question 13

how do we get to first normal form

Answer 13

flatten multivalued attributes into atomic ones
extend the primary key so it contains the new atomic attribute; making a composite key

Question 14

what is second normal form

Answer 14

1nf and every non prime attribute should be fully functionally dependent on the entire primary key

Question 15

how do we get to second normal form

Answer 15

of there is a partial dependency you need to make a new table

Question 16

what is third normal form

Answer 16

2nf and no non-prime attributes should depend on another non-prime attribute

Question 17

how do we get to third normal form

Answer 17

if theres a dependency between two non-prime attributes you need to make a new table with both of them and keep only one of them in the og table

Question 18

candidate key

Answer 18

minimal set of attributes that can be the primary key of the table

Question 19

prime attributes

Answer 19

any attribute part of the candidate key

Question 20

superkey

Answer 20

a set of attributes that uniquely identifies each row in the table

Question 21

what is the difference between a candidate key and a super key

Answer 21

candidate is minimal