Entity Relationship model (ER model) is a high-level data model. This model is useful to specify the data items and relationships for a specific system. It creates the conceptual architecture of a database. It also generates a data view that is relatively simple to construct. In ER modeling, the database structure is represented by an entity-relationship diagram.
The ER Model, which comprises of the following components, is used to model the system’s logical view from a data perspective:
Entity in Entity Relationship Model
An entity can be a physical item, such as a person, automobile, house, or employee, or it can be a conceptual object, such as a firm, a job, or a university course. An entity is an object of the Entity Type, and an entity set is a collection of all entities.
Attribute(s) in Entity Relationship Model
Attributes are the qualities that determine the entity type. For example, Roll No., Name, DOB, Age, Address, and Mobile No. are some of the characteristics that make up entity type Student. In an ER diagram, an oval is basically an attribute.
Key Attribute
The key attribute helps to represent an entity’s primary qualities. It generally stands for a primary key. An ellipse with the text underlined represents the key attribute.
Composite Attribute
An attribute that is consist of numerous other attributes is basically a composite attribute. An ellipse represents the composite attribute.
Multivalued Attribute
There can be several values for an attribute. A multivalued attribute is a type of attribute that has multiple values. In ER model a multivalued attribute is a double oval.
Derived Attribute
A derived attribute is an attribute that can be derived from another attribute. A dashed ellipse is there to depict it.
Relationship in Entity Relationship Model
The association between entity kinds is basically the relationship type. For example, the relationship type ‘Enrolled in’ exists between the entity types Student and Course. The relationship type is the diamond in the ER diagram, with lines linking the items.
The degree of a relationship set refers to the number of different entity sets that participate in it. Cardinality is the number of times an entity from an entity-set participates in a relationship-set.
