DBMS-Mapping Cardinalityone-to-one, one-to-many, many-to-one, or many-to-many.pptx

In database management systems (DBMS), mapping cardinality describes relationships between entities in entity-relationship diagrams. It signifies how instances of one entity relate to instances of another. Cardinality can be one-to-one, where each instance in one entity corresponds to one instance in another, one-to-many, where one instance links to multiple instances, many-to-one, where multiple instances relate to one, or many-to-many, where multiple instances from each entity can connect. Mapping cardinality is crucial for designing database schemas, ensuring data relationships are accurately represented and enabling efficient data retrieval and manipulation.Mapping cardinality in DBMS depicts how instances of one entity associate with instances of another, determining one-to-one, one-to-many, many-to-one, or many-to-many relationships.

1. MAPPING CARDINALITY: One-to-one One entity from entity set A can be associated with at most one entity of entity set B and vice versa. 1

2. EXAMPLE One-to-one relationship: A customer is associated with at most one loan via the relationship borrower A loan is associated with at most one customer via borrower 2

3. One-to-many One entity from entity set A can be associated with more than one entities of entity set B however an entity from entity set B, can be associated with at most one entity. 3

4. EXAMPLE In the one-to-many relationship a loan is associated with at most one customer via borrower , a customer is associated with several (including 0) loans via borrower 4

5. Many-to-one More than one entities from entity set A can be associated with at most one entity of entity set B, however an entity from entity set B can be associated with more than one entity from entity set A. 5

6. EXAMPLE In a many-to-one relationship a loan is associated with several (including 0) customers via borrower , a customer is associated with at most one loan via borrower 6

7. Many-to-many One entity from A can be associated with more than one entity from B and vice versa. 7

8. EXAMPLE: In many to many relationship, A customer is associated with several (possibly 0) loans via borrower A loan is associated with several (possibly 0) customers via borrower 8

9. Participation of an Entity Set in a Relationship Set Total participation (indicated by double line): every entity in the entity set participates in at least one relationship in the relationship set E.g. participation of loan in borrower is total every loan must have a customer associated to it via borrower Partial participation : some entities may not participate in any relationship in the relationship set E.g. participation of customer in borrower is partial 9

10. Alternative Notation for Cardinality Limits Cardinality limits can also express participation constraints 10