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A family view, meaning up to two parents and a list of children who have those parents in common.
Relationships carry the canonical information for this view, and the relationships must be used
to get Facts (lineage types, marriages, etc.) about the relationships covered by a Family.
The Family data type provides a convenient way to see the typical family views without having to do
the calculations to derive them. There should only be one family for each unique set of parents,
and only one for each single-parent family with a particular parent.