Entity-Relationship model in DBMS Theory - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an Entity in the Entity-Relationship model?

An Entity is a real-world object or thing that can be distinctly identified. It can be a person, place, event, or concept.

beginner

Define a Relationship in the Entity-Relationship model.

A Relationship shows how two or more entities are connected or associated with each other in the real world.

beginner

What is an Attribute in the Entity-Relationship model?

An Attribute is a property or characteristic of an entity or relationship, like a name, age, or date.

intermediate

Explain the concept of Cardinality in the Entity-Relationship model.

Cardinality defines the number of instances of one entity that can be associated with instances of another entity, such as one-to-one, one-to-many, or many-to-many.

beginner

What is a Primary Key in the context of the Entity-Relationship model?

A Primary Key is an attribute or set of attributes that uniquely identifies each entity instance in an entity set.

Which of the following best describes an Entity in the ER model?

A A property of a relationship

B A real-world object or thing

C A connection between two databases

D A type of database query

An Entity represents a real-world object or thing that can be identified distinctly.

What does Cardinality specify in an ER diagram?

A The number of instances of one entity related to another

B The number of relationships in the model

C The number of attributes an entity has

D The size of the database

Cardinality defines how many instances of one entity relate to instances of another entity.

Which symbol is commonly used to represent an Entity in an ER diagram?

A Rectangle

B Diamond

C Oval

D Arrow

Entities are usually shown as rectangles in ER diagrams.

What is the role of an Attribute in the ER model?

A To connect entities

B To represent database users

C To define database tables

D To describe properties of entities or relationships

Attributes describe the properties or characteristics of entities or relationships.

A Primary Key in an entity is used to:

A Describe the entity's attributes

B Link two entities

C Identify each entity instance uniquely

D Show the relationship type

The Primary Key uniquely identifies each instance of an entity.

Explain the main components of the Entity-Relationship model and their roles.

Think about objects, their connections, and properties.

Describe how cardinality affects the way entities relate to each other in an ER diagram.

Consider how many of one entity can connect to another.