URN Syntax
RFC 2141
| Document | Type |
RFC - Proposed Standard
(May 1997; Errata)
Was draft-ietf-urn-syntax (urn WG)
|
|
|---|---|---|---|
| Last updated | 2014-07-29 | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| Stream | WG state | (None) | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 2141 (Proposed Standard) | |
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | (None) | ||
| Send notices to | (None) | ||
Network Working Group R. Moats
Request for Comments: 2141 AT&T
Category: Standards Track May 1997
URN Syntax
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
Uniform Resource Names (URNs) are intended to serve as persistent,
location-independent, resource identifiers. This document sets
forward the canonical syntax for URNs. A discussion of both existing
legacy and new namespaces and requirements for URN presentation and
transmission are presented. Finally, there is a discussion of URN
equivalence and how to determine it.
1. Introduction
Uniform Resource Names (URNs) are intended to serve as persistent,
location-independent, resource identifiers and are designed to make
it easy to map other namespaces (which share the properties of URNs)
into URN-space. Therefore, the URN syntax provides a means to encode
character data in a form that can be sent in existing protocols,
transcribed on most keyboards, etc.
2. Syntax
All URNs have the following syntax (phrases enclosed in quotes are
REQUIRED):
<URN> ::= "urn:" <NID> ":" <NSS>
where <NID> is the Namespace Identifier, and <NSS> is the Namespace
Specific String. The leading "urn:" sequence is case-insensitive.
The Namespace ID determines the _syntactic_ interpretation of the
Namespace Specific String (as discussed in [1]).
Moats Standards Track [Page 1]
RFC 2141 URN Syntax May 1997
RFC 1630 [2] and RFC 1737 [3] each presents additional considerations
for URN encoding, which have implications as far as limiting syntax.
On the other hand, the requirement to support existing legacy naming
systems has the effect of broadening syntax. Thus, we discuss the
acceptable syntax for both the Namespace Identifier and the Namespace
Specific String separately.
2.1 Namespace Identifier Syntax
The following is the syntax for the Namespace Identifier. To (a) be
consistent with all potential resolution schemes and (b) not put any
undue constraints on any potential resolution scheme, the syntax for
the Namespace Identifier is:
<NID> ::= <let-num> [ 1,31<let-num-hyp> ]
<let-num-hyp> ::= <upper> | <lower> | <number> | "-"
<let-num> ::= <upper> | <lower> | <number>
<upper> ::= "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" |
"I" | "J" | "K" | "L" | "M" | "N" | "O" | "P" |
"Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" |
"Y" | "Z"
<lower> ::= "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" |
"i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" |
"q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" |
"y" | "z"
<number> ::= "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |
"8" | "9"
This is slightly more restrictive that what is stated in [4] (which
allows the characters "." and "+"). Further, the Namespace
Identifier is case insensitive, so that "ISBN" and "isbn" refer to
the same namespace.
To avoid confusion with the "urn:" identifier, the NID "urn" is
reserved and MUST NOT be used.
Moats Standards Track [Page 2]
RFC 2141 URN Syntax May 1997
2.2 Namespace Specific String Syntax
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