A relationship is some association between entities. In this section we shall concentrate on binary relationships. That is, associations between two entities. Relationships between one, three, four or N entities is also possible. In the E–R approach, more than one relationship can exist between any two entities.
Example: – The entities House and Person can be related by ownership and/or by occupation.In theory, having identified a set of say 6 entities, up to 15 relationships could exist between these entities. In practice, it will usually be obvious that many entities are unrelated