Referential integrity is used to join two tables like Primary Key & Foreign key relationship while designing the Schema.
If you dive deeply into Data Warehouse concepts,
We can define the the following relations
1 -1 : 1 Record of the right table have relationship with 1 record in the left table.
1 - N : 1 Record of the right table have relationship with more than 1 records in the left table.
1 - 0 :Outer Join,
Thanks for ur suggestion and answer