Modelagem de Dados - Comparando Entidades e Relações

Introduction to Data Modeling

In this section, Fábio Barbosa introduces the concept of data modeling and discusses the importance of entities in database design.

Entities and Relationships

• Entities are fundamental building blocks in data modeling.

• Entities represent real-world concepts that are modeled within a database.

• Relationships between entities can be complex, with multiple terms representing similar or slightly different concepts.

Entity Relationship Model

• The entity relationship model is a way to represent entities and their relationships in a database.

• A relation is a technical term used in databases to define a set of records or tuples that represent instances of an entity.

• Relations are represented as tables with rows and columns derived from an entity.

Attributes of Relations

• Each cell within a relation table contains a single value.

• Values within the same column have the same data type, known as the domain of the data.

• Instances of an entity within a relation table do not repeat; duplicates can be eliminated.

Examples of Relations

This section provides examples to illustrate relations and attributes in data modeling.

Car Example

• In the car example, each row represents an instance of a car entity.

• Columns in the table represent attributes such as manufacturer, model, and license plate.

• Each cell contains a single value corresponding to its intersection between row and column.

Attribute Domains

• Values within the same column have consistent data types or domains.

• For example, values in the "Manufacturer" column are textual while values in the "Price" column are monetary.

Eliminating Duplicate Instances

This section discusses how duplicate instances can be eliminated from relations.

Removing Duplicate Instances

• Duplicate instances refer to identical items within a database.

• Duplicate instances can be eliminated by keeping only one instance and removing the duplicates.

Example: Product Table

• In the product table, duplicate instances of the same product can be removed.

• The name and price of the product are attributes that should not have duplicate instances.

Relations as Tables

This section emphasizes that relations in data modeling are represented as tables.

Relation Creation Rules

• Tables in a database must follow specific rules and norms to be considered relations.

• Each table represents a relation derived from entities in data modeling.

Conclusion

The video concludes with a summary of relations and their importance in data modeling.

Recap on Relations

• Relations are tables derived from entities in data modeling.

• They represent instances of entities with specific attributes.

• Understanding relations is crucial for effective database design.