Every item a user must be able to fetch on its own is an identified item with at least one identifier, unique within a stated namespace; any identification scheme that guarantees uniqueness may be used (not only the ISO/IEC 6523-based one of earlier editions). The package models identified items, scoped identifiers and namespaces.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.