Parent is a type of Ancestor. Parent is a type of Person. Person wants (to) Mom. Mom is a different concept from Father. 
Husband is a type of Partner. Husband is related to Father. Father is related to Unit. Unit is related to Farm. 
Ancestor <--IsA-- Parent --IsA--> Person --Desires--> Mom <--DistinctFrom--> Father 
Partner <--IsA-- Husband <--RelatedTo--> Father <--RelatedTo--> Unit <--RelatedTo--> Farm 