The relationships in data sources are like BGR (Boy Girl Relationship). There are 3 types:
1) One boyfriend to One girlfriend
This is the easiest to manage because one record from one table is linked to another record in a second table.
2) One boyfriend to Many girlfriends OR Many boyfriends to One girlfriend
One record from one table is related to many records in a second table
3) Many boyfriends to Many girlfriends
Many records from one table are related to many records in a second table. The relationship is highly complex and should be avoid at all cost.