INFS1603 Lecture Notes - Lecture 4: Associative Entity, Unique Key, Foreign Key

• School: UNSW, UNSW Sydney
• Department: Information Systems
• Course: INFS1603
• Professor: All

Document Summary

Participants: are the entities that participate in the relationship. The relationship name is an active or passive verb. Each relationship is identified by a name that describes the relationship: a relationship degree indicates the number of entities or participants associated with a relationship, unary, binary, ternary and quaternary. The relationship between entities can be: one to one, one to many, many to many, recursive (relationship can exist between occurrences of the same entity set) Connectivity is used to describe the relationship classification. The er diagram indicates connectivity by using a numeric notation -> (1:1), (1:m), (m:n). Cardinality expresses the minimum and maximum number of entity occurrences associated with one occurrence of the related entity. Cardinality is usually expressed in the format (x,y) If expressed in the form (1,n) it implies there is no limit to the number of associations. Option al vs man dator y re lationship partic ipation.