4. Implications

For a URN specification to be acceptible, it must meet the previous requirements. We draw a set of conclusions, listed below, from those requirements; a specification that satisfies the requirments without meetings these conclusions is deemed acceptable, although unlikely to occur.

• To satisfy the requirements of uniqueness and scalability, name assignment is delegated to naming authorities, who may then assign names directly or delegate that authority to sub-authorities. Uniqueness is guaranteed by requiring each naming authority to guarantee uniqueness. The names of the naming authorities themselves are persistent and globally unique and top level authorities will be centrally registered.

• Naming authorities that support scalable naming are encouraged, but not required. Scalability implies that a scheme for devising names may be scalable both at its terminators as well as within the structure; e.g., in a hierarchical naming scheme, a naming authority might have an extensible mechanism for adding new sub-registries.

• It is strongly recommended that there be a mapping between the names generated by each naming authority and URLs. At any specific time there will be zero or more URLs into which a particular URN can be mapped. The naming authority itself need not provide the mapping from URN to URL.

• For URNs to be transcribable and transported in mail, it is necessary to limit the character set usable in URNs, although there is not yet consensus on what the limit might be.

In assigning names, a name assignment authority must abide by the preceding constraints, as well as defining its own criteria for determining the necessity or indication of a new name assignment.