January 30, 2020
Amitraj
Various Symbols Used In ER Diagram -
Entity
Simple rectangular box represents an Entity.
Relationships between Entities - Weak and Strong
Rhombus is used to setup relationships between two or more entities.
Attributes for any Entity
Ellipse is used to represent attributes of any entity. It is connected to the entity.
Weak Entity
A weak Entity is represented using double rectangular boxes. It is generally connected to another entity.
Key Attribute for any Entity
To represent a Key attribute, the attribute name inside the Ellipse is underlined.
Derived Attribute for any Entity
Derived attributes are those which are derived based on other attributes, for example, age can be derived from date of birth.
To represent a derived attribute, another dotted ellipse is created inside the main ellipse.
Multivalued Attribute for any Entity
Double Ellipse, one inside another, represents the attribute which can have multiple values.
Composite Attribute for any Entity
A composite attribute is the attribute, which also has attributes.
Notation of ER diagram
Database can be represented using the notations. In ER diagram, many notations are used to express the cardinality. These notations are as follows:
Entity
Simple rectangular box represents an Entity.
Relationships between Entities - Weak and Strong
Rhombus is used to setup relationships between two or more entities.
Attributes for any Entity
Ellipse is used to represent attributes of any entity. It is connected to the entity.
Weak Entity
A weak Entity is represented using double rectangular boxes. It is generally connected to another entity.
Key Attribute for any Entity
To represent a Key attribute, the attribute name inside the Ellipse is underlined.
Derived Attribute for any Entity
Derived attributes are those which are derived based on other attributes, for example, age can be derived from date of birth.
To represent a derived attribute, another dotted ellipse is created inside the main ellipse.
Multivalued Attribute for any Entity
Double Ellipse, one inside another, represents the attribute which can have multiple values.
Composite Attribute for any Entity
A composite attribute is the attribute, which also has attributes.
Notation of ER diagram
Database can be represented using the notations. In ER diagram, many notations are used to express the cardinality. These notations are as follows:
