1. A method of creating relationships within a network-based system for making recommendations, the method comprising: accessing a first related object and a second related object calculating a relationship score for a relationship between the first and second related objects; selecting a relationship type, using the relationship score, representing the relationship between the first and second related objects, the selected relationship type including at least one of a complement relationship type, indicating complementary relationship between the first and second related objects, and a substitute relation type, indicating a substitutionary relationship between the first and second related objects; storing the selected relationship type representing the relationship between the first related object and the second related object; and using the selected relationship type to provide a recommendation within the network-based system.