Types of DBMS Entities

Entities play a critical role in the organization and storage of data in database management systems (DBMS). These entities, which are effectively data containers, exist in various flavors customized to certain data-handling requirements. Tangible Entities represent physical objects, while Intangible Entities encapsulate abstract concepts. Strong Entities stand-alone with unique identifiers, whereas Weak Entities rely on strong entities for identification. Understanding these entity types is pivotal in building a robust database system aligned with your data needs.

Example of Entity in DBMS

Before learning about the entity types in DBMS, let us first get to know about entities with some examples.

Entities are essential for structuring data in Database Management Systems (DBMS). Think of them as virtual containers for information about physical things, concepts, or events. They form the basis for constructing database tables, defining data characteristics, and establishing relationships between entities.

For example, in a library database, a Book is an entity with unique attributes like title, author, publishing date, and ISBN. Entities don't operate in isolation; they interact with other entities through relationships. In our library database, a relationship might connect the Book entity with the Borrower entity to track who borrowed which book.

Entities are fundamental for organized databases, ensuring data integrity and efficient data retrieval. They simplify complex information into manageable components, enabling DBMS to store, retrieve, and modify data reliably. So, when you borrow a book, remember that entities work behind the scenes to keep everything orderly.

Kinds of Entity in DBMS

Before learning about the entity types in DBMS, let us get to familiar with the kinds of entities in DBMS.

Entities are critical in Database Management Systems (DBMS) for properly organizing and storing data. Based on their physical or conceptual nature, entities are usually categorized into two types: Tangible Entities and Intangible Entities. Let's take a look at these ideas in a more clear approach.

Tangible Entity

This category includes tangible items that can be felt, seen, or measured. Consider it to be anything you can perceive with your senses. Books, CDs, and even persons borrowing such products can all be considered physical entities in a library database. Because these entities have well-defined traits and attributes, they may be represented in a DBMS.

Intangible Entity

Intangible entities, conversely, are abstract notions or ideas that cannot be felt or quantified in a concrete sense. They frequently only exist in the domain of information. Intangible entities in a database management system might incorporate notions such as borrower history or membership status. These entities are essential for simulating complicated interactions and settings where physical items alone cannot convey the complete picture.

When constructing a database, it is critical to understand the distinction between physical and immaterial items. It ensures that your DBMS appropriately represents the real-world data it handles, making it a vital tool for effectively storing and retrieving information.

Types of DBMS Entities

Let us learn about the entity types in DBMS.

Entities are the building pieces that help organize and store data efficiently in Database Management Systems (DBMS). Based on their independence and relationship with other entities within a database model, there are two main categories of entities: Strong Entities and Weak Entities. Let's go through each using code-based examples to help you understand these ideas.

Strong Entity

A strong entity is an entity that has a distinctive, unique attribute known as a primary key. This primary key is used to uniquely identify each instance of the entity in the database. For instance, in a library database, the entity Book can be considered a strong entity because it has a primary key, such as the International Standard Book Number (ISBN), which uniquely identifies each book.

In SQL, you can create a table for a strong entity like this:

Here, ISBN serves as the primary key, ensuring each book has a unique identifier.

Weak Entity

Conversely, a weak entity does not possess a unique primary key on its own. Instead, it relies on a related strong entity to provide a portion of its identification. A classic example is the Page entity within the context of a Book entity. Pages within a book can be uniquely identified only within the scope of that specific book.

In SQL, a table for a weak entity may look like this:

Here, PageNumber alone is not enough to uniquely identify a page. It relies on the BookISBN (foreign key) to ensure uniqueness, linking it back to the Book entity.

Note: A weak entity is represented with a double rectangle or double box in the diagram. This indicates its dependence on a strong entity. Inside the double box, attributes specific to the weak entity are listed. Weak entities often have a partial key, which is represented as a dashed underline or some other distinguishing mark to show it's not a full primary key. A relationship is drawn from the weak entity to the strong entity with a diamond shape, indicating that the weak entity is linked to the strong entity through an identifying relationship.

Example

Let us take an example of entity types in DBMS for more clarity.

Suppose we have two entity types EMPLOYEES and DEPENDANT (children of the employee).

• An employee can have one or more dependents. A dependent cannot exist without an employee.
• The employee entity is a strong entity because it has a primary key (Emp_id).
• The dependent entity is a weak entity because it does not have a primary key of its own.
• The name attribute of the dependent entity is a partial key that, along with the Emp_id attribute of the employee entity, can uniquely identify each dependent entity.
• The relationship between the employee entity and the dependent entity is an identifying relationship, which means that each dependent entity must be associated with an employee entity.