A data structure may have several records linked to the same logical data structure. I might read in a list of orders, some of which are for the same customer. When I have sharing like this, I can represent it by treating the customer either as a value or as a reference. With a value, the customer data is copied into each order; with a reference, there is only one data structure that multiple orders link to. If the customer never needs to be updated, then both approaches are reasonable. It is, perhaps, a bit confusing to have multiple copies of the same data, but it’s common enough to not be a
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