What is entity in DBMS? - Its Definition, types, and examples

Data is the new oil of the digital age, running companies, inspiring innovation and informing decision making. Nonetheless, managing such huge amount of data is not an easy task. This where Database Management System (DBMS) comes in. A DBMS does more than just storing and retrieving data, it ensures its security, integrity and accessibility.

One of the basic ideas in DBMS is that of 'entity'. It is important for everyone who is engaged with a DBMS to understand what an entity means, how it operates and its place in a database. The present article intends to clarify entity notion in DBMS by providing uniform definition on this topic as well as describing its attributes, types and role in Entity-Relationship (ER) model.

This post will be relevant whether you are student dipping toe into database world or professional trying to refresh your knowledge or technology enthusiast simply wanting to know more about it. Thus let us go on this amazing adventure to discover everything there is to know about entities in DBMS.

Understanding DBMS

A DBMS is a type of software that helps users to describe, construct, uphold and control admittance to the database. It holds an interface between the database and the end-users or the application programs making sure that data is regularly organized and remains easily accessible.

The DBMS plays an important role in managing both data and technology for managing those data. It offers step-by-step procedures for creating, updating, retrieving and managing data within a database.

Various types of DBMS exist including Relational DBMS (RDBMS), Hierarchical DBMS (HDBMS), Network DBMS (NDBMS), and Object-oriented DBMS (OODBMS). Among them all, RDBMS is the most widely applied system which enables one to keep data in tables form.

In case of RDBMS entity is a fundamental concept. An entity represents any real-world object or idea such as student or course in university’s database with different from others. Every entity has attributes or properties that give it its identity. For instance, a student entity may have such attributes as name, age and course.

Concept of Entity in DBMS

In DBMS context, a database management system (DBMS) 'entity' is an actual object or idea that can be distinguished. It is anything that exists independently and has its own unique existence in which it can be identified. For example, entities may include students, professors, courses and departments in the university database. Each entity consists of one or more 'attributes', which refer to the properties of the entity like a student's name or a course's title.

Entities are made up of 'attributes'. 'Attributes' are what we call the characteristics of an entity. For example, student might have attributes such as name, age and grade of a student. These attributes help to distinguish one entity from another.

There are several types of entities in DBMS:

1. Strong Entity: This is an entity which can exist independently within itself in a database having a primary key. For example, the strong entity here would be Student while Student_ID would serve as its primary key.

2. Weak Entity: It is another kind of an entity which relies on other things to exist. It does not have any primary key but it has some discriminator that is set of attributes for making it distinct. For example "Grade" can rely on Student thereby serving as weak entity with Subject as its discriminator till needed by others by telling something else about them than usual for most purposes.

3. Composite Entity: A composite entity represents relationship between other entities and is used when the relationship needs to have attributes. For example, Enrollment may be considered as a composite entity representing the relationship between students and courses.

4. Derived Entity: Derived entities are those whose values are calculated from other entitie's attributes. For example, there can be an "Average_Grade" derived entity computed from the "Grade" entity.

Entity Sets

An 'Entity Set' in a Database Management System (DBMS) is a collection of similar types of entities. An entity set may contain entities that share certain attributes. For example, the 'Student' entity set may include all students of a university.

Typically, an entity set is defined by its entity type. The entity type specifies the schema or blueprint for the entity set and what attributes entities in the set will have. The entity type for instance, for the 'Student' sets might specify that the entities in the set have attributes such as: Name, Age, Course among others.

It's worth noting that there is a difference between an entity and an entity set. While an entity stands for one object or single idea, an entity set symbolizes numerous corresponding objects or ideas. For example John, Emma and Robert are some entities but they make up to an entity set when they are put together on basis of common attribute like 'student'.

Attributes of an Entity

In DBMS, a "field" is an attribute of an entity that denotes its property or characteristic. For example, attributes of "student" could be like "name", "age" and etc. Each attribute has a value. For example, the name of a student can either be 'John' or 'Emma'.

Different types of attributes in DBMS are:

• Simple Attribute: Simple attribute is one which cannot be divided into sub parts for example 'age'.

• Composite Attribute: Composite attribute is one that can be divided into several smaller meaningful components like address which is made up of 'street', 'city', 'state' and 'country'.

• Derived Attribute: Derived attribute whose value is generated from some other attributes. Such as if in database there are 'Date_of_Birth' and 'Current_Date' then 'Age' can become derived attribute.

• Multi-valued Attribute: A multi-valued attribute may have more than one value such as 'Phone_Number' being an example in case of 'Student' entity where it happens that students may have more than one phone number.

Entity-Relationship Model

Entity-relationship (ER) model is a conceptual instrument employed for illustrating database's data structures. It is an abstract and conceptual representation of data which defines data elements and their relationships.

The ER model has three basic concepts on which it is based:

1. Entities: As we discussed earlier, an entity is a real-world object or concept that can be distinctly identified. In an ER diagram, entities are usually represented by rectangles.

2. Attributes: Attributes refer to characteristics or qualities that describe an entity. In an ER diagram, attributes are represented by ovals connected to their entity rectangle.

3. Relationships: Relationships determine how one entity associates with others. In an ER diagram, relationships are indicated using diamonds that are attached to the related entities through lines.

ER model assists in designing databases as it offers a designer with a kind of blueprint at the level of concept regarding how some pieces of information relate to one another. For example, in a university's database 'Students', 'Courses', and 'Faculty' could be entities while 'Enrolls in' and 'Teaches' may be relationships between them.

Conclusion

This blog post explores the idea of an 'entity' in a Database Management System (DBMS). It has been established that an entity is something that can be defined. This post has also examined various different types of entities - 'Strong', 'Weak', 'Composite' and 'Derived' which play different roles in a DBMS.

In addition, we have focused on "entity sets" and attributes applicable to an object. Those attributes enable distinguishing one object from another one and playing a fundamental role in the organization of data inside DBMS.

At lastly, we consider the Entity-Relationship (ER) model as conceptual tool illustrating database requirements for data structures. The ER model helps to understand how entities, attributes and relationships come together to build up a complete picture of how information is connected in a DBMS.