We are rediscovering rationale for both hard and symbolic links. Define semantics of something like hard links. It doesn t have to be in a collection. But allow our version of hard links point to a directory. A hard link points to an underlying resource, and allows multiple URLs to be bound to a resource in such a way that MOVE doesn t affect any other bindings.
Hard links provide localized reliable binding.
We won t do that. What we care about is the underlying notion that multiple collections can have members bound to the same resource. Talk independently of Unix. The motivation for references is to provide the ability to reliably share a resource. When you change it, anyone using any reference to it will see the change.