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The diagram is recursive and has three “routes”, going from the one entity set “Person” to a relationship type “Parent’s” (so there’s three lines going to the relationship type).
The question we’re given is to take this trinary relationship and split it up into binary relationships, assumingly three.
I was thinking of taking ‘person’ as an entity set and having child of being the relational type to another entity set parents with an attribute for each parent.
Could someone aid me slightly?
So, if I understand correctly, each Person has three foreign key references to the Parent table, and you want to normalize that.
My approach would be to abstract this relationship into a cross-reference entity, PersonParent. PersonParent would have three fields: the Person’s ID, the Parent’s ID, and the “type” of parent this Parent is to the Person (this last bit of information was implicit in the field for each of the three references in the old schema). A Parent can be so to many People, but one Person can only have between 0 and a finite N (probably 3) Parents, by specifying the combination of PersonID and ParentType as unique, and specifying a maximum number of valid ParentTypes. ParentType can be a reference to an entity containing these types, or the valid values can be built in as a check constraint (I highly recommend the former).