Data Entities: Cardinalities & Keys Flashcards
1
Q
What is a Cardinality of a relationship?
A
How many instances of an entity relate to one instance of the other entity
2
Q
Cardinality examples:
A
1..1, 1..*, ..
3
Q
What is a primary key?
A
The attribute that uniquely identifies an entity
4
Q
What is a foreign key?
A
Links attributes in other entities
5
Q
What’s the relationship between primary and foreign key in a 1..* relationship?
A
The primary key from the “1 end” is added as foreign key in the “many end”
6
Q
What’s the relationship between primary and foreign key in a 1..1 relationship?
A
Both ends may have the same primary key
7
Q
How are relationships between entities created?
A
Created by keys and are represented by storing the primary key values in the other entity
