RFC 2141 (rfc2141) - Page 2 of 8
URN Syntax
Alternative Format: Original Text Document
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:
::= [ 1,31 ]
::= | | | "-"
::= | | ::= "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"
::= "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"
::= "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