Database Modeling: Objects and Attributes Quiz

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Questions and Answers

What is a characteristic of a strong entity?

Dependent on another entity

Cannot exist on its own

Does not have a unique identifier

Has its own unique identifier (correct)

How is a weak entity different from a strong entity?

Has a unique identifier

Can exist on its own

Exists independently of other entities

Dependent on a strong entity (correct)

What does a double underline in an entity box signify?

Unique identifier

Strong entity

Partial identifier (correct)

Weak entity

In the context of identifying relationships, what do they link together?

Strong entities to weak entities Signup and view all the answers

When should a relationship with attributes become an associative entity?

When it links two strong entities together Signup and view all the answers

What is an entity in the context of a database?

An object that will be composed of multiple attributes Signup and view all the answers

Which of the following is a characteristic of identifiers (keys) in a database?

Will uniquely identify individual instances of an entity type Signup and view all the answers

What does a composite attribute refer to in a database?

An attribute broken into component parts Signup and view all the answers

In the context of attributes, what does 'single-valued' imply?

An attribute has a single, unique value for each entity Signup and view all the answers

What is the purpose of an identifier (key) in a database?

To uniquely identify individual instances of an entity type Signup and view all the answers

How are identifiers (keys) differentiated from other attributes in a database?

They uniquely identify individual instances of an entity type Signup and view all the answers

What describes features pertaining to the association between entities in a relationship?

Relationship types Signup and view all the answers

In the E-R model, what is the degree of a relationship?

The number of entity types participating in the relationship Signup and view all the answers

What type of relationship involves three different entity types related to each other?

Ternary Relationship Signup and view all the answers

What does 'One-to-Many' cardinality mean in a relationship?

An entity can have many related entities on one side Signup and view all the answers

What defines the minimum number of instances one entity can be associated with another in an E-R diagram?

Cardinality Constraints Signup and view all the answers

In an E-R model, what is an instance between specific entity instances?

Relationship instance Signup and view all the answers

Which type of constraint specifies the maximum number of instances one entity can be associated with another in a relationship?

Cardinality Constraints Signup and view all the answers

What does a Unary Relationship involve in the E-R model?

One entity related to another of the same entity type Signup and view all the answers

What is represented by Multiple Relationships in an E-R diagram?

Entities related to each other in more than one way Signup and view all the answers

How is 'Many-to-Many' cardinality defined in a relationship?

An entity can have many related entities on both sides Signup and view all the answers

Study Notes

Entity Characteristics

A strong entity has a unique existence, independent of other entities.
A weak entity, on the other hand, exists only in relation to another entity.

Entity Representation

A double underline in an entity box signifies a weak entity.

Relationships

Relationships link together entities.
A relationship with attributes becomes an associative entity when it has its own attributes.

Entity Definition

In the context of a database, an entity is an object or concept that has existence and can be described with a set of attributes.

Identifier (Key) Characteristics

An identifier (key) is a unique characteristic that distinguishes one entity from another.
Identifiers (keys) are differentiated from other attributes by being unique and non-null.

Attribute Characteristics

A composite attribute is made up of multiple simpler attributes.
A single-valued attribute implies that each entity instance has only one value for that attribute.

Identifier (Key) Purpose

The purpose of an identifier (key) is to uniquely identify each instance of an entity.

Relationship Descriptions

Features pertaining to the association between entities in a relationship are described by relationship attributes.

E-R Model Concepts

The degree of a relationship refers to the number of entities involved in the relationship.
A ternary relationship involves three different entity types related to each other.
One-to-Many cardinality means that one instance of an entity can be associated with multiple instances of another entity.
The participation constraint defines the minimum number of instances one entity can be associated with another in an E-R diagram.
A unary relationship involves only one entity type.
Multiple relationships are represented by multiple lines connecting entities in an E-R diagram.
Many-to-Many cardinality means that multiple instances of one entity can be associated with multiple instances of another entity.
The cardinality constraint specifies the maximum number of instances one entity can be associated with another in a relationship.

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Description

Test your understanding of objects in database modeling, focusing on instances in the database and attributes. Identify what should and should not be considered as entities in database modeling.