INST 311 Lecture Notes - Lecture 9: Cardinality
Document Summary
Name of the relationship is written inside the diamond-box. All the entities (rectangles) participating in a relationship, are connected to it by a line. A relationship where two entities are participating is called a binary relationship . Cardinality is the number of instance of an entity from a relation that can be associated with the relation. One-to-one when only one instance of an entity is associated with the relationship, it is marked as "1:1". The following image reflects that only one instance of each entity should be associated with the relationship. One-to-many when more than one instance of an entity is associated with a relationship, it is marked as "1:n". The following image reflects that only one instance of entity on the left and more than one instance of an entity on the right can be associated with the relationship. Many-to-one when more than one instance of entity is associated with the relationship, it is marked as "n:1".