The "Universal Resource Name" is currently (March 1993) under development in the IETF. A requirements specification is in preparation. It currently looks as though it will be a short string suitable for encoding in URI syntax, for which case the "urn:" prefix is reserved. The URN shall be encoded precisely as defined in the (future) URN standard, except in that:
If the URN has a hierarchical nature, then the slash delimiter shall be used in the URI encoding;
If the URN has a hierarchical nature, the most significant part shall be encoded on the left in the URI encoding;
Any characters with reserved meanings in the URI syntax shall be escape encoded
These rules of course apply to any URI scheme. It is of course possible that the URN syntax will be chosen such that the URI encoding will be a 1-1 transcription.
An example might be a name such as
but the reader should refer to the latest URN drafts or specifications.