We observed that in TMF 622 Product Ordering API, in Product Resource model, Characteristic resource is in aggregation relationship with cardinality 0..* with Product meaning that a Product can have multiple characteristics associated to it with each specifying a "value" attribute (This value attribute is missing in the resource model Characteristic in the resource model for Product).
But, we couldn't see any reference from these characteristics to the characteristicSpecifications (productOfferingCharacteristic or prodSpecCharValueUse). As per our understanding, this would be needed in cases where we have multiple product offerings with different characteristic specifications associated to them. Having this relationship would help -
I take it that you are referring to gen5 APIs, I think I can see this from the diagrams you attached. So:
The link between characteristic and characteristic spec is logical, by the name property. This is not new, it's been like this for as long as I have been involved in the Open API project, and probably longer still (many years already). The idea is that the Product has a reference to its originating offering or spec, and you should then be able to find the characteristic spec for a characteristic using the name property.
Hope this clarifies things for you.