Modelagem de Dados - O que são Cardinalidades

Name: Modelagem de Dados - O que são Cardinalidades
Uploaded: 2017-09-14T11:28:48.000Z
Duration: 32 min 15 s

Introduction to Cardinality in Data Modeling

In this section, the instructor introduces the concept of cardinality in data modeling. Cardinality refers to the number of items that can be related between entities. The instructor explains that cardinality can be maximum or minimum, representing the maximum and minimum number of instances that can participate in a relationship.

Understanding Cardinality

Cardinality represents the quantity or number of items that can be related between entities.

It can be maximum or minimum, indicating the maximum and minimum number of instances that can participate in a relationship.

Maximum cardinality defines the maximum number of instances an entity can have in a relationship.

Minimum cardinality defines the minimum number of instances from an entity that must participate in a relationship.

Representing Cardinality

In Entity-Relationship diagrams using Chen's notation, cardinalities are represented within parentheses as two numbers: minimum and maximum.

Alternatively, a single number can represent both minimum and maximum cardinalities.

Another notation called "chicken feet" notation uses vertical lines and circles to represent zero, one, or many instances.

Examples of Cardinalities

Example 1: One-to-One Relationship

Minimum cardinality: 1

Maximum cardinality: 1

Example 2: One-to-Many Relationship

Minimum cardinality: 1

Maximum cardinality: Many

Example 3: Zero-to-One Relationship

Minimum cardinality: 0

Maximum cardinality: 1

Example 4: Zero-to-Many Relationship

Minimum cardinality: 0

Maximum cardinality: Many

Applying Cardinalities

Determining the cardinalities involves considering how many instances from one entity can relate to another entity.

For example, in a relationship between "client" and "order," we can determine that a client can have many orders (One-to-Many), and an order can only be placed by one client (Zero-to-One).

Applying Cardinality to Example Relationship

In this section, the instructor applies cardinality to an example relationship between "client" and "order." The goal is to determine the minimum and maximum cardinalities for each entity in the relationship.

Applying Cardinality to Client-Order Relationship

For the "client" entity:

Minimum cardinality: 1 (at least one order)

Maximum cardinality: Many (can have multiple orders)

For the "order" entity:

Minimum cardinality: 1 (must be associated with a client)

Maximum cardinality: 1 (can only be placed by one client)

Representing Cardinalities using Chen's Notation

Using Chen's notation, we represent the cardinalities as follows:

Client(1, Many) -- Order(1, 1)

Alternative Representation using Chicken Feet Notation

Alternatively, we can represent the same cardinalities using chicken feet notation:

Client --|< Order

One-to-One Relationship Example

In this section, the instructor explains a specific type of relationship called a one-to-one relationship. A one-to-one relationship occurs when each instance of one entity is related to exactly one instance of another entity.

One-to-One Relationship Example

Example: Professor-Armchair Relationship

Each professor uses exactly one armchair.

Minimum cardinality for armchair: 1

Maximum cardinality for armchair: 1

Minimum cardinality for professor: 1

Maximum cardinality for professor: 1

Representing One-to-One Relationship using Chen's Notation

Using Chen's notation, we represent the one-to-one relationship as follows:

Professor(1, 1) -- Armchair(1, 1)

Conclusion and Recap

In this section, the instructor concludes the topic of cardinality in data modeling and recaps the key points discussed.

Key Points

Cardinality refers to the number of items that can be related between entities.

It can be maximum or minimum, indicating the maximum and minimum number of instances that can participate in a relationship.

Cardinalities are represented using Chen's notation or chicken feet notation.

Examples of cardinalities include one-to-one, one-to-many, zero-to-one, and zero-to-many relationships.

Cardinalities help in determining how entities are related and are important for database normalization.

By understanding cardinality, we can effectively model relationships between entities in a database.

Understanding One-to-One Relationships

In this section, the speaker explains the concept of one-to-one relationships in database modeling.

One-to-One Relationships

A one-to-one relationship means that for each instance of one entity, there is only one corresponding instance in another entity.

The relationship can be represented using Chen's notation or extended representation.

Chen's notation uses a line connecting the entities, while the extended representation includes minimum and maximum cardinality on both sides of the relationship.

This type of relationship is useful when there is a unique association between two entities.

Exploring One-to-Many Relationships

This section focuses on understanding one-to-many relationships in database modeling.

One-to-Many Relationships

In a one-to-many relationship, an occurrence in one entity can be associated with multiple instances in another entity.

This type of relationship is represented by a line connecting the entities with a crow's foot symbol indicating "many" on the side of the "many" entity.

An example given is the relationship between employees and departments, where an employee works in only one department but a department can have multiple employees.

Many-to-Many Relationships and Entity Creation

Here, we learn about many-to-many relationships and how to handle them through entity creation.

Many-to-Many Relationships

A many-to-many relationship occurs when multiple instances from one entity are associated with multiple instances from another entity.

This type of relationship requires creating a new entity to transform it into two separate one-to-many relationships.

For example, in a customer-package scenario, where customers can purchase multiple packages and packages can be bought by multiple customers, we create an intermediate entity to represent this relationship.

Importance of Relationship Cardinality and Normalization

The speaker emphasizes the importance of relationship cardinality in database modeling and its role in normalization.

Relationship Cardinality and Normalization

Relationship cardinality helps determine the occurrences of entities and aids in database normalization.

When dealing with a many-to-many relationship, it is necessary to create a new entity to transform it into one or two one-to-many relationships.

This process simplifies the implementation of many-to-many relationships in databases.

Determining the correct entities and their relationships is crucial for effective database design.

Conclusion

The speaker concludes by summarizing the topics covered in this video on data modeling.

Conclusion

This video provided an introduction to different types of relationships in database modeling, including one-to-one, one-to-many, and many-to-many relationships.

Understanding relationship cardinality is essential for proper entity representation and normalization.

Creating intermediate entities can help handle many-to-many relationships effectively.

Further topics related to data modeling will be covered in future videos.

Project Modeling and Training

The speaker discusses the possibility of creating a complete modeling project from start to finish and applying the concepts learned in the training.

Importance of Practical Application

The speaker emphasizes the importance of practical application in learning.

They mention the idea of creating a complete modeling project from beginning to end.

Applying the concepts learned in the training is encouraged.

Call to Action

Viewers are invited to subscribe to the channel for further training.

They are also encouraged to visit a specific website or resource.