What are entity sets?

Answered by Douglas Hiatt

Entity sets are an essential concept in the field of database management and are used to organize and group instances of an entity type. An entity type represents a distinct type of real-world object, such as a person, a product, or an event. Entity sets act as logical containers for instances of these entity types, allowing for efficient organization and retrieval of data.

To better understand entity sets, let’s consider an example. Imagine we have an entity type called “Employee” which represents individual employees in a company. The entity set for this employee type would be a collection of all the individual employee instances within the organization. Each instance would represent a specific employee and contain attributes such as their name, employee ID, and job title.

Entity sets can also include instances of any type derived from the original entity type. This means that we can have subsets of the main entity set that represent specific categories or subtypes of the original entity type. Continuing with our employee example, we could have derived entity sets such as “Manager” or “Intern” which contain instances of employees who hold those specific roles within the company.

One important aspect of entity sets is that they provide a way to uniquely identify and distinguish between different instances of the same entity type. In our employee example, each employee instance would have a unique employee ID, allowing us to differentiate between individual employees within the entity set.

Entity sets also enable relationships between different entity types. For instance, in our employee example, we could have another entity type called “Department” and establish a relationship between the Employee entity set and the Department entity set. This relationship could represent the fact that each employee is assigned to a specific department within the company.

Entity sets are logical containers that hold instances of an entity type and any derived types. They help organize and group related data, allow for unique identification of instances, and enable the establishment of relationships between different entity types.