ER Model
ER Diagram is also called entity relationship diagram or ERD and it is a high-level data model. This model is used to define the data elements and relationships for a specified system.
It develops a conceptual design for the database. it also develops a very simple and easy-to-design view of data.
in ER modeling the database structure is portrayed as a diagram called an entity-relationship diagram.
It shows the relationship of entity sets in a database and also it helps to describe the logical structure of the database.
Normally it looks like a flowchart but an ER diagram has many shapes and it represents a specific meaning.
For example, Suppose we design a school database. In this database, the student will be an entity with attributes like address, name, id, age, etc. The address can be another entity with attributes like city, street name, pin code, etc and there will be a relationship between them.
The ER diagram is created based on the three concepts, they are
- Entity
- Relationship
- Attributes
The ER diagram has a different shape with specific meaning like entity represent rectangle and the oval represent attributes and also diamond represents the relationship.
Entity:
An entity may be any object, class, person, or place. In the ER diagram, an entity can be represented as rectangles.
consider a school as an example- teacher, employee, department staffed, etc. can be considered an entity.
Attribute
the attribute is used to describe the property of an entity. usually, an eclipse is used to represent an attribute.
for example, student id, age, phone number are considered as an attribute.
They are pointed as four types, they are
- key attribute
- composite attribute
- multivalued attribute
- derived attribute
Relationship
A relationship is used to describe the relation between entities. diamond or rhombus is used to represent the relationship.
Types of relationship
- Ono-to-one relationship
- One-to-many relationships
- Many-to-one relationship
- Many-to-many relationship
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