3. Requirements for URN encoding

In addition to requirements on the functional elements of the URNs, there are requirements for how they are encoded in a string:

• Single encoding: The encoding for presentation for people in clear text, electronic mail and the like is the same as the encoding in other transmissions.

• Simple comparison: 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.

• Human transcribability: For URNs to be easily transcribable by humans without error, they should be short, use a minimum of special characters, and be case insensitive. (There is no strong requirement that it be easy for a human to generate or interpret a URN; explicit human-accessible semantics of the names is not a requirement.) For this reason, URN comparison is insensitive to case, and probably white space and some punctuation marks.

• Transport friendliness: A URN can be transported unmodified in the common Internet protocols, such as TCP, SMTP, FTP, Telnet, etc., as well as printed paper.

• Machine consumption: A URN can be parsed by a computer.

• Text recognition: The encoding of a URN should enhance the ability to find and parse URNs in free text.