Master-detail cascade delete and restore
Key Takeaway
Deletion cascades only downward: deleting a master record also deletes its detail and subdetail records, and undeleting the master record brings them back.
In a master-detail relationship, the master (parent) record controls the life of its detail (child) records. So deleting or undeleting one record can also affect the records related to it. The order of deletes affects whether a record can come back.
How a master-detail relationship links objects
A master-detail relationship links objects tightly. The master record controls certain behaviors of its detail and subdetail records. The detail object can't work as a stand-alone object. You always create the master-detail relationship field on the detail object.