Entity Relationship Model (ERM)
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1
Introduced by Chen in 1976, what is the ERD considered to be?
A widely accepted graphical tool for data modeling
2
What components are depicted in an ERD?
Entities, Attributes, Relationships
3
How is an entity represented in an ERD?
By a rectangle containing the entity’s name
4
How are attributes represented in the Chen model?
As ovals connected to the entity
5
How are attributes represented in the Crow’s Foot model?
In an attribute box below the entity rectangle
6
What is a simple attribute?
An attribute that cannot be subdivided
7
What is a composite attribute?
An attribute that can be subdivided
8
What is a single-valued attribute?
An attribute that can have only one value
9
What is a multivalued attribute?
An attribute that can have multiple values and requires a new table to store them
10
What is a derived attribute?
An attribute whose value can be calculated from other attributes
11
What does connectivity describe?
The relationship classification (1:1, 1:M, M:N)
12
What does cardinality express?
The minimum and maximum number of entity occurrences allowed, defined by business rules
13
What conditions define a weak entity?
It is existence-dependent and its primary key is partially or totally derived from the parent entity
14
What is optional participation in a relationship?
An entity occurrence does not require a corresponding occurrence in the related entity
15
What is mandatory participation?
An entity occurrence requires a corresponding occurrence in the related entity
16
What is a unary or recursive relationship?
A relationship within a single entity set
17
What is a binary relationship?
A relationship between two entities
18
What is a ternary relationship?
A relationship involving three entities
19
What is a quaternary relationship?
A relationship involving four entities
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