Databaser

Question 1

Cartesian Product:

Person x Country

{
(1, “Linus”, “Rudbeck”, 27),
(2, “Jerome”, “Landre”, 103),
(3, “Mira”, “Pop”, 46)
}
The content of the table Country is:
{
(27, “Sweden”),
(46, “Romania”),
(103, “France”)
}

Answer 1

{
(1, ”Linus”, ”Rudbeck”, 27, 27, ”Sweden”),
(1, “Linus”, “Rudbeck”, 27, 46, “Romania”),
(1, “Linus”, “Rudbeck”, 27, 103, “France”),
(2, “Jerome”, “Landre”, 103, 27, “Sweden”),
(2, “Jerome”, “Landre”, 103, 46, “Romania”),
(2, “Jerome”, “Landre”, 103, 103, “France”),
(3, “Mira”, “Pop”, 46, 27, “Sweden”),
(3, “Mira”, “Pop”, 46, 46, “Romania”),
(3, “Mira”, “Pop”, 46, 103, “France”)
}

Question 2

What is the generic name of the “rectangles” in ER diagrams?

Answer 2

Entity

Question 3

What is the generic name of the “diamonds” in ER diagrams?

Answer 3

Relations

Question 4

What is the generic name of the “ellipses” in ER diagrams?

Answer 4

Attributes

Question 5

What is the generic name of the underlined elements in ER diagrams?

Answer 5

Primary key

Question 6

What is the generic name of “0:”? Explain what “0”, “1” (not present in this diagram but possible in other diagrams) and “” represent in ER diagrams?

Answer 6

• Cardinalites
• min = 0
• max = *

Question 7

JSON:

[ ]

Answer 7

Array

Question 8

JSON:

{ }

Answer 8

Object

Question 9

JSON:

“key”:”value”

Answer 9

A key/value pair separated by :

Question 10

JSON:

” “

Answer 10

A character string

Question 11

JSON:

,

Answer 11

Separator between objects and key/value pairs

Question 12

Please write the answer in the text box below and give an example of a movies variable in JSON containing an array of three movies, each movie has a “title”, a “director”, and a “year”, fill in the information of each book as “realistic” data:

Answer 12

{
“movies”: [
{“title”: “Inception”, “director”: “Chistopher Nolan”, “year”: 2010},
{“title”: “The Matrix”, “director”: “Lana Wachowski, Lilly Wachowski”, “year”: 1999},
{“title”: “Parasite”, “director”: “Bong Joon-ho”, “year”: 2019}
]
}

Question 13

What do we need for 1NF?

Answer 13

• Only one value per cell
• No repeating groups

Question 14

What do we need for 2NF?

Answer 14

• 1NF
• PK is a single column attribute

Question 15

What do we need for 3NF?

Answer 15

• 2NF
• No transitive dependencies

Question 16

What are the advantages to have a database in 3NF?

Answer 16

To avoid problems when you insert, delete and update

Question 17

Closure:

We have the relation
R0 = {A, B, C, D, E, F}
and the functional dependencies
F0 = { {A} → {C}, {C} → {F}, {D,E} → {B}, {F} → {D, E} }

• Compute the closure {A}+
• Compute the closure {B}+
• Compute the closure {C}+
• What is the primary key?

Answer 17

{A}+ = {A, C, F, D, E, B}
{B}+ = {B}
{C}+ = {C, F, D, E, B}

• A is the primary key

Question 18

What does each letter of CRUD mean?

Answer 18

C = Create
R = Read
U = Update
D = Delete