Week 11-12: Cardinality Constraints in Database

Cardinality constraint defines the maximum number of relationship instances in which an entity can participate.

Types of Cardinality Ratios-

  1. Many-to-Many cardinality (m:n)
  2. Many-to-One cardinality (m:1)
  3. One-to-Many cardinality (1:n)
  4. One-to-One cardinality (1:1 )

1. Many-to-Many Cardinality-

By this cardinality constraint,

  • An entity in set A can be associated with any number (zero or more) of entities in set B.
  • An entity in set B can be associated with any number (zero or more) of entities in set A.

2. Many-to-One Cardinality-

By this cardinality constraint,

  • An entity in set A can be associated with at most one entity in set B.
  • An entity in set B can be associated with any number (zero or more) of entities in set A.

3. One-to-Many Cardinality-

By this cardinality constraint,

  • An entity in set A can be associated with any number (zero or more) of entities in set B.
  • An entity in set B can be associated with at most one entity in set A.

4. One-to-One Cardinality-

By this cardinality constraint,

  • An entity in set A can be associated with at most one entity in set B.
  • An entity in set B can be associated with at most one entity in set A.

 

 

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lecture-7-weak-and-strong-entity-types.pptx (0.32 MB )

lecture-8-cardinalities-constraints.pptx (0.21 MB )