Structural Constraints

Multiplicity

Multiplicity refers to the set of rules that define how entities in one entity type can relate to entities in another. It consists of two elements:

• Cardinality: The maximum number of times an entity can participate in a relationship.
• Participation: Determines whether participation in a relationship is mandatory or optional.

Multiplicity

Common Degrees of Relationships

• One-to-One (1:1): Each instance in one entity relates to only one instance in another.
• One-to-Many (1:*): One entity instance relates to many instances in another entity.
• Many-to-Many (:): Multiple instances of one entity can relate to multiple instances of another.

Examples:

• Staff manages Branch (1:1)
• Staff oversees PropertyForRent (1:*)
• Newspaper advertises PropertyForRent (*:*)

One to One relationship

One to Many Relationship

Many to Many Relationship

Multiplicity as cardinality and participation constraints