The encoding for presentation for people in clear text, electronic mail and the like is the same as the encoding in other transmissions. A comparison algorithm for URNs is simple, local, and deterministic. That is, there is a single algorithm for comparing two URNs that does not require contacting any external server, is well specified and simple. For this reason, URN comparison is insensitive to case, and probably white space and some punctuation marks. Implications For a URN specification to be acceptible, it must meet the previous requirements.
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. 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. 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.