Conditions are:
1) The child record should have all the key fields of parent
record and at least one more key field other than the key fields of parent
record.
2) We should mention the parent record in the record
properties of child record.
3) We can not go for more than three levels of parent/child
relationships.
Advantages are:
1) To have referential integrity.
2) No need to enter information again and again
