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What is entity in a Database Management System (Explained in Detail!)


Do you know what is an entity in the Database Management System (DBMS) is? An entity is a practical matter or it is a real-life item that may be differentiated from other real-life items. As an example, a vehicle is an asset. We know the distinctive features of an entity by its attribute. As an example, a Red vehicle characteristic has an attribute which is its color and its value is red.

Scope of the Article

In this article, we will describe what is the entity in Data Base Management System. It will also be discussed what are the various types of entities, what are the entity sets and how we can differentiate them from the entity.

Entity set

An entity set is a set in a database management system that jointly represents a group of the same type of entities. For instance, an asset group that contains automobiles, an asset group that includes bank accounts, and so on. In the tabular demonstration of statistics in the DBMS, the whole table is an entity set, at the same time as every row of this desk is considered an entity.

Weak Entity Set

In a database management system, an entity set with no primary key is considered a weak entity set. It shows that in the entity set, each entity is not uniquely represented by an attribute.

As an example: a group of vehicles having different attributes like the name of the vehicle, and the color of the vehicle, will be considered a weak entity due to the fact two vehicles can have a similar name and similar color. Consequently, both of the attributes cannot be taken as a primary key, and resultantly this entity set will be weak.

A powerful set of entity

In a database management system, the powerful set is the entity set that has the primary key, which means there exists an attribute that may distinctively represent each part of the entity in the Database Management System (DBMS)

for instance: a set of vehicles that have different features with distinctive attributes like registration plate number, and brand of a vehicle are solid features because there can no two different vehicles with the same registration number and brand with color. So the attribute vehicle registration number may be taken as the primary key and consequently, this entity set will be powerful.

Real asset Non-Real asset

Entities are placed in database tables. Every table will incorporate a set of entities or a list of all entities taken into consideration to be the same. As an example, in the database of a university, the staff can be at one table and the students can be at other. If your database has entities that have the same attributes, you can gather them in one entity set and gather them in the same particular table.

One of the standards for figuring out whether or not something is an entity is that it may be easily distinguished from different entities; it is that the table will have only distinctive entities.

If you need to work along with your database, you need to have the ability to distinguish every entity from all different entities. They require statistics that explain how they stay inside the actual world. The manner to distinguish table entities from every other is through attributes.

How the attributes and entities are differentiated?

Every entity has its separate row, however, all entities in a given table will proportion the same workable attributes. these attributes are the supports of the table. An entity is defined by these attributes. An employee table can comprise attributes like the title of work, telephone number, home address, and name.

Every entity must have a key attribute, to keep its specialty. According to our employee details table, the identity number of the employee may be a key attribute. No two personnel have the same worker identity number, even though they’re unusually same in all different attributes.

A primary key is not the only type of key. You should additionally take note of terms like primary, advanced, secondary, composite, foreign, candidate, and alternate keys. Every key out of them does a special task. For this time, it will be useful to understand that the key attributes are the candidate keys on the table and that the primary key is the entity set identifier chosen from one of these candidate keys. As an example, the identification number of a worker can be a single primary key, at the same time another key is the number of social protection. The developer of the database can pick out each, but in maximum cases, it will likely be more secure to apply the identification number of an employee even if their social security number is unique.

There are also certain restrictions on every attribute regarding the value it can hold. Those attribute domains are policies that ensure that the entity is successfully identifiable. Area restrictions for our worker database can ensure that an employee identity is a definite length and consists of only definite characters or that an e-mail address is comprised of @ sign without spaces. Carefully designed domains make sure that database entities turn out to be with legitimate information and save you from future issues.

You can get more detailed information about the asset type with the presence of the main attribute. it is a strong type of entity if it has a key attribute, it is a sturdy entity kind, and if it does no longer have a key characteristic, it’s miles a weak entity kind and it can be settled with a strong type of entity. can simplest be set by a strong entity type? You may also outline a strong entity as an autonomous entity and a weak entity as is not independent.

In the above employee example, the address may be an attribute. However, additionally a country, a nation, a state, a city, and many others. It can additionally be an entity made from unique features. The management entity depends upon the employee entity so the management will be a weak entity because it needs employees to exist.

Accordingly, you have various types of entity, weak and strong or dependent and independent. Attribute entity is another type of entity in the Database Management System (DBMS). This gives additional facts about any other entity. Attribute entities additionally referred to as qualifying entities might also comprise attributes that are not always contained inside the parent entity, but may be placed along with it. For instance, it may be elements utilized in a car. By way of storing the parts in a functioning entity, you could make changes to the elements independently placing no effect on the entity of the vehicle model.

There are a few types of Attributes you should be aware of. The attributes which are derived from the areas of atomic values are called simple types of attributes; these are the attributes also known as mono valued. The attributes that contain a chain of command attributes are called Compound attributes. For instance, in the database, the address can comprise a number, a street, and an area. Therefore, it will be written as → Address = {78 + ‘Donald Street’ + ‘Kingsford’}.

Multivalued attributes are the attributes that comprise a group of values for every attribute. The Derived attributes contain values planned after other attributes. The Age can be derived from the Date of Birth attribute. In this case, the date of birth is termed as the stored attribute, stored physically in the database. There are numerous forms of features. Consequently, a database entity needs its attributes to differentiate it from different entities. This permits your database to outline how entities engage with one another.

What are the different forms of database entities?

Database items can be divided into real and non-real entities. If the entity exists physically inside the actual world, then it is for real. A boy is real, just like a town. If it logically exists in the actual global, then it is immaterial. Further, the work is not touchable so it is non-real.

How do database entities engage?

Developing an entity-relationship diagram (ERD) can help us to know all about its working. An ERD permits you to plan all the entities that will be existing in your database, listing their attributes, recognizing the connections among the entities, and making it clear that you recognize precisely what you are going to draft.

Keys and types

Critical asset challenge is the key. A key’s an attribute or set of attributes whose values may be used to uniquely discover an entity in a fixed of entities. There are several forms of keys. A primary secret’s a simple or complex, particular and minimal key. it is specific due to the fact no two table rows will have an equal value. it’s far minimum because each column is wanted to gain forte. A composite key carries greater attributes, however, should be minimal. A number one key’s a candidate key chosen by means of the database dressmaker for use as an identity mechanism for all entities. It needs to uniquely perceive the tuples within the table and can’t be empty. In the example below, the number one key’s EID:

Employee (EID, call, surname, SIN, address, telephone, date of birth, income, employee number.

An attribute (can be created) that is used for search purposes only, for example, Phone and Name is called a secondary key. Alternate keys are all candidate keys that are not selected as primary keys. A foreign key (FK) is a property in one table that references a primary key in another table OR it can be null. The foreign key and primary key must have the same data type.

In the following example from the COMPANY database, Department ID is the foreign key:

Employee (EID, first name, last name, SIN, address, phone, date of birth, salary, service number)


The Entity Relationship Modeling (ERM) process is difficult and quickly becomes more difficult when you have so many different types of resources, each containing a wealth of information on different topics. If you use multiple sources, it’s a good idea to avoid creating source-specific entities: for example, if you use censuses and tax lists that both contain information about people, don’t create two tables for people (one from one source and one from another). Stick to the abstract logic of information – people are important to your research, so put information about all people in one place. Not only does this make sense, but it also makes it easier to find data about specific people later (manually or using queries): it’s easier to find a person if the person is found in one table, not in several.

No entity-relationship diagram (ERD) will ever be perfect, and like many things in database design, it will be a matter of trade-offs. The success of an ERD is something that can only be determined in one way – once the database has accomplished the tasks it was intended and designed for, and that will only happen once. once it starts entering and using the database for analysis.