* A relationship is an association among two or more entities.diamond
* A collection of similar relationships is called a relationship set.
* For example, ‘Branch’ and ‘Staff’ can be associated with a relationship ‘Has’.
* Relationship occurrence – a uniquely identifiable association, which includes one occurrence from each participating entity type.
Relationship type – diagrammatic representation
Shown as a line connecting the associated entity types, labelled with the name of the relationship.
First letter of each word in the entity name is uppercase.
Normally a relationship is named using a ‘verb’ or ‘verb group’.
The direction in which the relationship makes sense is marked using an ‘arrow’.
Degree of Relationship type
The number of participating entity types in a relationship.
Relationships can be classified based on their degree into
Binary – relationship with two participants
Ternary – relationship with three participants
Quaternary – relationship with four participants
Degree of a relationship is the number of participating entities in the relationship.
A relationship of degree two is called a binary relationship (e.g. Works In).
A relationship with degree three is called ternary.