Structural constraints define how relationships between entities are structured, and they impose restrictions on the participation and cardinality of entities within relationships.
• These constraints specify the rules that must be followed when entities participate in relationships, determining how many instances of one entity type can be associated with instances of another entity type.
There are two key types of structural constraints in the ER model:
- Mapping Cardinality Constraint
- Participation Constraint (or Existence Dependency)
1.) Mapping Cardinality Constraint
Cardinality constraints define the number of instances of one entity that can or must be associated with each instance of another entity in a relationship.
It can of different types:
- One-to-one
- One-to-many
- Many-to-one
- Many-to-many
One-to-one:
