GPT E/R Model

Question 1

Who developed the E/R model and what is its purpose?

Answer 1

Peter Chen in 1976 for conceptual database design using graphical representation

Question 2

What are the core constructs of the E/R model?

Answer 2

• Entity
• Relationship
• Attribute

Question 3

Entity

Answer 3

Class of objects with common properties and unique name

Question 4

Relationship

Answer 4

Logical link between two or more entities

STUDENT “attends” COURSE

Question 5

Attribute

Answer 5

Propoerties of entities or relationships

Name, BirthDate, etc.

Question 6

Cardinality constraints

Answer 6

Rules specifying minimum and maximum participation in relationships or attributes

Why attributes too? Well we have recursive relationships?

Question 7

Weak entity

Answer 7

An entity that depends on another entity for identification

Primary key the foreign key

Order Item is a weak entity to Order for example

Question 8

Composite attributes

Answer 8

Aggregate of multiple attributes

City + Street = Address

Question 9

Recursive relationships

Answer 9

Entity relates to itself

PERSON “friends” PERSON

Question 10

Generalization in the E/R Model

Answer 10

A hierarchy where child entities inherit properties from a parent entity.

Question 11

Data Dictionary

Answer 11

Documentation of entities, relationships, and their attributes with descriptions

Question 12

Two types of E/R notations

Answer 12

DB-Main and Crow’s Foot

Question 13

Main limitations of E/R model

Answer 13

• Cannot express all integrity constraints
• Requires additional documentation to bridge design gaps

Question 14

How is E/R model used in reverse engineering?

Answer 14

To analyze and redesin existing databases lacking conceptual-level documentation

Question 15

Ternary relationship

Answer 15

A relationship involving three entities

Question 16

What is an identifier in the E/R model?

Answer 16

An attribute or combination of attributes that uniquely identify an entity

Primary Key

Question 17

What is a subset in E/R Modeling?

Answer 17

A special hierarchy where a specialized class (STUDENT) is a subset of a parent entity (PERSON)

Don’t get how this hierarchy is special

Question 17

Why is documentation important in E/R modeling?

Answer 17

To supplement the model’s expressiveness and ensure clarity in design and implementation

Question 18

What kind of key does a weake entity use?

Answer 18

A composite key that includes a foreign key from the strong entity

Question 19

Entity-level cardinality

For my own confusion I added this card

Answer 19

General rules about how many isntances of an entity can relate to another entity

How we see it modeled, but enforced at instance level

Most of the time its only one instance from an entity thats relating to another soooo, i mean otherwise it would be a many to many relationships requiring another table

Question 20

Implicit constraints

Answer 20

Inherent design to E/R model

Question 21

Explicit constraints

Answer 21

Defined by database designer to enforce business rules

Question 22

When is it necessary to create a relationship table?

Answer 22

• Many-Many relationships
• Relationships have attributes (ENROLLMENT includes EnrollmentDate)