- Two relations, A and B
- A side, B side, 1 side, N side
- 1:1 relationships
- Key can go on either side
- 1:N relationships
- Key cannot go on 1 side
- Has to go on N side
- M:N relationships
- Nowhere obvious for the key to go
- Create new pairing relation
In Focus
1.3.06. Relationships in the relational model