Week 1

Question 1

What is a Database Management System (DBMS)?

Answer 1

Provides efficient, reliable, convenient, safe, multi-user friendly storage and access to massive amounts of persistent data.

Question 2

What is an Entity Relationship Model

Answer 2

A graphical representation of the logical view of a Database

Question 3

What is an Entity?

Answer 3

An object that has distinguishable properties,
An entity must have attributes
Entity use Rectangular shape

Question 4

What is an entity set?

Answer 4

A conceptual representation of entities w.r.t the same set of attributes

Question 5

What is an attribute?

Answer 5

Property that distinguishes an entity, is represented with an oval shape

Question 6

What attribute distinguishes an entity (the whole row) within the entity set Car?

Answer 6

“Model” uniquely identifies an entity (the whole row) within this entity set.
The attribute that uniquely identifies an entity within this entity set is called a “key attribute” (represented with solid underlines)

Question 7

What are Candidate keys? In the photo, which attributes that can be called Candidate keys?

Answer 7

Candidate keys are the set of all possible key attributes. In the photo above, (Model,Length)

Question 8

What is a Derived attribute? What is a Multi-valued attribute?

Answer 8

A derived attribute is an attribute that is computed from another attribute. Represented with a dashed line.
A multi-valued attribute is an attribute that have multi-values, represented with double lines.

Question 9

What is a Relation?

Answer 9

A logical model for associating two or more Entities.

Question 10

What is a Relation set?

Answer 10

It covers all such relations between two or more Entity sets. It is represented with a diamond.

Question 11

What is a Degree of a relationship set?

Answer 11

The number of entity sets that participate in a relationship

Question 12

What is a Binary relationship?

Answer 12

A relationship that involves two entity sets.

Question 13

What is a Ternary relationship sets?

Answer 13

A relationship that involve three entity sets

Question 14

What is a Unary relationship set?

Answer 14

A relationship that involves an entity that have a relationship with its own entity

Question 15

What are the 4 types of cardinalities in a relationship?

Answer 15

1. 1:1 (one-to-one)
2. 1:N (one-to-many)
3. N:1 (many-to-one)
4. N:N (many-to-many)

Question 16

What is the cardinality of this relationship?

Answer 16

1:1

Question 17

What is the cardinality of this relationship?

Answer 17

1:N, One car be repaired by many mechanics, A mechanic can repair one car.

Question 18

What is the cardinality of this relationship?

Answer 18

N:1 One car be repaired by a mechanic, A mechanic can repair many cars.

Question 19

What is the cardinality of this relationship?

Answer 19

N:N, One car can be repaired by many mechanics, A mechanic can repair many cars

Question 20

What is a Total Participation?

Answer 20

Shows that it is mandatory for the entity who link with a total participation (Identified with a double line) to be in the relationship

Question 21

What is a Partial Participation?

Answer 21

Shows that it is not compulsory for entity that linked with a partial participation (identified with a single line) to be in the relationship

Question 22

What is a weak entity?

Answer 22

A weak entity is an entity that is dependent on a strong entity, meaning that a weak entity cannot be in the table without it strong entity. It is denoted with a double line square.
The weak entity does not have a primary key, instead, it uses a compound key which is a concatenation of its attribute with the primary key of its dependent entity. The weak entity key used in the compound key is denoted with a dashed underline.

Question 23

What is an ISA?

Answer 23

An extended ER Hierarchies that is used for adding descriptive attributes specific to a subclass.