Introduction to ER Model in DBMS
The Entity Relationship model is considered as conceptual diagram which is used for representing the database structure and the components of database. The ER Model in DBMS contains the entities, attributes and relationships which is similar to tables, rows and columns of database. The ER Model in DBMS acts as blueprint for designing the database structure. The primary use for creating ER model is to represent the relationship among the data in the database. The ER model is considered as high-level model for representation of data. The complex database structure can be easily represented in form of entity relationship model.
Explain the entity of ER Model in DBMS
In the Entity relationship model the entity is considered as object that exist in real world and can be identified easily. In the ER model, the entity has related attributes which help the entity to be easily identified. The similar entity forms a cluster known as entity set. In the entity set the entities contains the attributes which can have similar type value. For e.g. teacher set may contain all teachers in the school. One of the main property of entity set is that it not need to be disjoint. For example in student database, the student name, student age, student contact number, student address are all considered as entity which is sued to identify each student uniquely.
There are basically two types of entity that are defined in below section:
- Strong entity
The strong entity is type of entity that does not require other entity for uniquely identify and use primary key for identification. In the ER diagram the strong entity are shown by rectangle. And the group of strong entity is known as strong entity set.
- Weak entity
For the ER model the weak entity is defined as the type of entity that cannot be identified uniquely by the attributes and needs the foreign key which combines with attributes to form the primary key. In the ER diagram the weak entity set is shown by rectangle of double line which is bold and double line is used to connect weak entity set to attributes. The relation among strong and weak entity is shown by double diamond in ER diagram.
Attributes of ER Model in DBMS
In the ER model, the attributes are the fields that are related to entity and used for describing the property of entity. The attributes are represented by eclipse in ER model. For example employee entity the employee name, employee age, employee number can be considered as attributes for employee entity.
Types of attributes that are defined below:
- Simple attribute
This category of attribute contains the atomic value and also cannot be further broken into other attributes. For example, employee’s contact number. This attribute cannot be further broken in other sub attribute and contain atomic values.
- Composite attribute
This category of attribute contains group of attribute to form a single attribute. The composite attribute can be further divided into other attribute. For example, employee name can attribute can be break into employee first name attribute and employee last name attribute.
- Derived attribute
This category of attribute deals with virtual attributes that means these attributes does not exist in database physically. These attributes can be derived some other type of attributes that are exist in the database. For example, employee date of birth attribute stored in database and from this attribute the employee age can be easily derived from employee date of birth attribute. The other example is employee salary attribute and from this attribute the average salary can be easily calculated to form new attribute average salary attribute that does not stored in database.
- Multivalued attribute
This category of attribute contains multiple value. For example, employee can have more than one contact number or email ids.
Explain the Relationship of ER Model in DBMS
In the ER model, there exist entities, attributes and relationship. And in between entities there exist association which is called as relationship. For example, teacher teaches student. Here teaches is considered as relationship among teacher and student entity. As in relationship there are number of entities that can be involved and on the basis of that degree can be defined for the relationships. For example, group of two entities is called binary relationship, group of three entities is called ternary relationship and till further.
In below section, the different types of relationship are described here:
- One to one
In one to one relationship, one entity can be directly associated to only one entity. It means the entity P can be associated with entity Q or vice versa. For example, One Man carry married to one woman or vice versa.
- One to many
In one to many relationship, one entity can be associated to more than one entity at same time. It means the entity P can be linked to multiple entities of Q but the entity Q can be linked to at least one P entity. For example, one teacher teaches to multiple student at same time but one student should at least taught by one teacher.
- Many to one
In many to one relationship, more than one entity of entity set P can be associated to only one entity Q. It means more than one entity from one entity set can be linked to only one entity. For example, students goes to school which means more than one student goes to same school.
- Many to Many
In many to many relationship, more than one entity from entity set P is linked to more than one entity of entity set Q. For example, group of students get taught by group of teachers. Here many to many relationship exist among students and teachers.
The ER Model in DBMS is considered as basic model for representation of the database. The ER model contains entities, attributes and relationship in entity relationship diagram. The entities are similar to table in database, attributes are like columns of database. For complex database structure, the ER model are best solution for designing the database in simpler way.
This is a guide to ER Model in DBMS. Here we discuss the introduction to ER Model in DBMS, explanation of entity, relationship and attributes. You can also go through our other related articles to learn more –