DBMS Notes

Cardinality and Modality

Cardinality and modality are two different terms in Database, let see one one by

Term Cardinality

it shows the maximum number of entities in one entity set, which can be associated with the number of entities of another entity set.

Maximum Cardinality can be one or many.

  • One: the cardinality of one tells that single instance of an entity. The symbol of vertical line | is use for one cardinality.
  • Many: the cardinality of many indicates the multiple instances of an entity. The symbol of crow foot () is used for many cardinality.

Term Modality

 Minimum number of instances of one entity set which can associate with each instance of other entity set is known as modality.

Minimum modality can be Zero (Optional) or One (Mandatory)

  • Optional: the Modality of Zero tells that no instance of an entity. Represented by small circle.
  • Mandatory: it indicates that single instance of an entity. Represented by vertical line |.

ER Diagram For Cardinality And Modality

From the Entity side, first symbol represent the cardinality and second represent the modality. ER Diagram and their notations are explain below

 Let explain Some more examples of cardinality and modality in ER Model

Example: 01 Student applies for group

Many or At least one student must applies for Group and similary and Many or At least one group must assign for Student. It is a many to many relationship example

Example 02: Student Deposits FEE

One or many student can deposit fee for a specific group but fee deposit by a student for a specific group will always be only one.

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