The Parent-Child Pattern should be used when you need to capture a logical relationship between two entities that meets the criteria of a Parent-Child relationship. For example, the Parent-Child Pattern is used to model the relationship between Income evidence and Income Usage evidence. An Income record for the money received by the client must exist before an Income Usage record for how that money was spent can be created. The money received could be spent to pay a number of bills, so the Income record can have multiple Income Usage records associated with it.