< draft-ietf-urn-syntax-04.txt		draft-ietf-urn-syntax-05.txt >
	Internet-Draft Ryan Moats		Internet-Draft Ryan Moats
	draft-ietf-urn-syntax-04.txt AT&T		draft-ietf-urn-syntax-05.txt AT&T
	Expires in six months March 1997		Expires in six months March 1997
	URN Syntax		URN Syntax
	Filename: draft-ietf-urn-syntax-04.txt		Filename: draft-ietf-urn-syntax-05.txt
	Status of This Memo		Status of This Memo
	This document is an Internet-Draft. Internet-Drafts are working		This document is an Internet-Draft. Internet-Drafts are working
	documents of the Internet Engineering Task Force (IETF), its		documents of the Internet Engineering Task Force (IETF), its
	areas, and its working groups. Note that other groups may also		areas, and its working groups. Note that other groups may also
	distribute working documents as Internet-Drafts.		distribute working documents as Internet-Drafts.
	Internet-Drafts are draft documents valid for a maximum of six		Internet-Drafts are draft documents valid for a maximum of six
	months and may be updated, replaced, or obsoleted by other		months and may be updated, replaced, or obsoleted by other
	skipping to change at page 2, line 10 ¶		skipping to change at page 2, line 10 ¶
	it easy to map other namespaces (which share the properties of URNs)		it easy to map other namespaces (which share the properties of URNs)
	into URN-space. Therefore, the URN syntax provides a means to encode		into URN-space. Therefore, the URN syntax provides a means to encode
	character data in a form that can be sent in existing protocols,		character data in a form that can be sent in existing protocols,
	transcribed on most keyboards, etc.		transcribed on most keyboards, etc.
	2. Syntax		2. Syntax
	All URNs have the following syntax (phrases enclosed in quotes are		All URNs have the following syntax (phrases enclosed in quotes are
	REQUIRED):		REQUIRED):
	<URN> ::= "urn:" <NID> ":" <NSS>		URN ::= "urn:" NID ":" NSS
	where <NID> is the Namespace Identifier, and <NSS> is the Namespace		where NID is the Namespace Identifier, and NSS is the Namespace
	Specific String. The leading "urn:" sequence is case-insensitive.		Specific String. The leading "urn:" sequence is case-insensitive.
	The Namespace ID determines the _syntactic_ interpretation of the		The Namespace ID determines the _syntactic_ interpretation of the
	Namespace Specific String (as discussed in [1]).		Namespace Specific String (as discussed in [1]).
	RFC 1630 [2] and RFC 1737 [3] each presents additional considerations		RFC 1630 [2] and RFC 1737 [3] each presents additional considerations
	for URN encoding, which have implications as far as limiting syntax.		for URN encoding, which have implications as far as limiting syntax.
	On the other hand, the requirement to support existing legacy naming		On the other hand, the requirement to support existing legacy naming
	systems has the effect of broadening syntax. Thus, we discuss the		systems has the effect of broadening syntax. Thus, we discuss the
	acceptable syntax for both the Namespace Identifier and the Namespace		acceptable syntax for both the Namespace Identifier and the Namespace
	Specific String separately.		Specific String separately.
	2.1 Namespace Identifier Syntax		2.1 Namespace Identifier Syntax
	The following is the syntax for the Namespace Identifier. To (a) be		The following is the syntax for the Namespace Identifier. To (a) be
	consistent with all potential resolution schemes and (b) not put any		consistent with all potential resolution schemes and (b) not put any
	undue constraints on any potential resolution scheme, the syntax for		undue constraints on any potential resolution scheme, the syntax for
	the Namespace Identifier is:		the Namespace Identifier is:
	<NID> ::= <let-num> [ 1,31<let-num-hyp> ]		NID ::= let-num [ 1*31let-num-hyp ]
	<let-num-hyp> ::= <upper> | <lower> | <number> | "-"
	<let-num> ::= <upper> | <lower> | <number>		let-num-hyp ::= letter / number / "-"
	<upper> ::= "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" |		let-num ::= letter / number
	"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" |		letter ::= %x41..5A / %x61..7A
	"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" |		number ::= %x30..39
	"8" | "9"
	This is slightly more restrictive that what is stated in [4] (which		This is slightly more restrictive that what is stated in [4] (which
	allows the characters "." and "+"). Further, the Namespace		allows the characters "." and "+"). Further, the Namespace
	Identifier is case insensitive, so that "ISBN" and "isbn" refer to		Identifier is case insensitive, so that "ISBN" and "isbn" refer to
	the same namespace.		the same namespace.
	To avoid confusion with the "urn:" identifier, the NID "urn" is		To avoid confusion with the "urn:" identifier, the NID "urn" is
	reserved and MUST NOT be used.		reserved and MUST NOT be used.
	2.2 Namespace Specific String Syntax		2.2 Namespace Specific String Syntax
	As required by RFC 1737, there is a single canonical representation		As required by RFC 1737, there is a single canonical representation
	of the NSS portion of an URN. The format of this single canonical		of the NSS portion of an URN. The format of this single canonical
	form follows:		form follows:
	<NSS> ::= 1*<URN chars>		NSS ::= 1*URN_chars
	<URN chars> ::= <trans> | "%" <hex> <hex>		URN_chars ::= trans / ("%" hex hex)
	<trans> ::= <upper> | <lower> | <number> | <other> | <reserved>		trans ::= letter / number / other / reserved
	<hex> ::= <number> | "A" | "B" | "C" | "D" | "E" | "F" |		hex ::= number / %x41..46 / %x61..66
	"a" | "b" | "c" | "d" | "e" | "f"
	<other> ::= "(" | ")" | "+" | "," | "-" | "." |		other ::= "(" / ")" / "+" / "," / "-" / "." /
	":" | "=" | "@" | ";" | "$" |		":" / "=" / "@" / ";" / "$" / "_" /
	"_" | "!" | "*" | "'"		"!" / "*" / "'"
	Depending on the rules governing a namespace, valid identifiers in a		Depending on the rules governing a namespace, valid identifiers in a
	namespace might contain characters that are not members of the URN		namespace might contain characters that are not members of the URN
	character set above (<URN chars>). Such strings MUST be translated		character set above (URN_chars). Such strings MUST be translated
	into canonical NSS format before using them as protocol elements or		into canonical NSS format before using them as protocol elements or
	otherwise passing them on to other applications. Translation is done		otherwise passing them on to other applications. Translation is done
	by encoding each character outside the URN character set as a		by encoding each character outside the URN character set as a
	sequence of one to six octets using UTF-8 encoding [5], and the		sequence of one to six octets using normalized UTF8 [5], and the
	encoding of each of those octets as "%" followed by two characters		encoding of each of those octets as "%" followed by two characters
	from the <hex> character set above. The two characters give the		from the hex character set above. The two characters give the
	hexadecimal representation of that octet.		hexadecimal representation of that octet.
	2.3 Reserved characters		2.3 Reserved characters
	The remaining character set left to be discussed above is the		The remaining character set left to be discussed above is the
	reserved character set, which contains various characters reserved		reserved character set, which contains various characters reserved
	from normal use. The reserved character set follows, with a		from normal use. The reserved character set follows, with a
	discussion on the specifics of why each character is reserved.		discussion on the specifics of why each character is reserved.
	The reserved character set is:		The reserved character set is:
	<reserved> ::= '%" | "/" | "?" | "#"		reserved ::= '%" / "/" / "?" / "#"
	2.3.1 The "%" character		2.3.1 The "%" character
	The "%" character is reserved in the URN syntax for introducing the		The "%" character is reserved in the URN syntax for introducing the
	escape sequence for an octet. Literal use of the "%" character in a		escape sequence for an octet. Literal use of the "%" character in a
	namespace must be encoded using "%25" in URNs for that namespace.		namespace must be encoded using "%25" in URNs for that namespace.
	The presence of an "%" character in an URN MUST be followed by two		The presence of an "%" character in an URN MUST be followed by two
	characters from the <hex> character set.		characters from the <hex> character set.
	Namespaces MAY designate one or more characters from the URN		Namespaces MAY designate one or more characters from the URN
	skipping to change at page 4, line 38 ¶		skipping to change at page 4, line 25 ¶
	these characters are RESERVED for future developments. Namespace		these characters are RESERVED for future developments. Namespace
	developers SHOULD NOT use these characters in unencoded form, but		developers SHOULD NOT use these characters in unencoded form, but
	rather use the appropriate %-encoding for each character.		rather use the appropriate %-encoding for each character.
	2.4 Excluded characters		2.4 Excluded characters
	The following list is included only for the sake of completeness.		The following list is included only for the sake of completeness.
	Any octets/characters on this list are explicitly NOT part of the URN		Any octets/characters on this list are explicitly NOT part of the URN
	character set, and if used in an URN, MUST be %encoded:		character set, and if used in an URN, MUST be %encoded:
	<excluded> ::= octets 1-32 (1-20 hex) | "\" | """ | "&" | "<"		excluded ::= octets 1-32 (1-20 hex) / "\" / """ /
	| ">" | "[" | "]" | "^" | "`" | "{" | "|" | "}" | "~"		"&" / "<" / ">" / "[" / "]" / "^" /
	| octets 127-255 (7F-FF hex)		"`" / "{" / "|" / "}" / "~" /
			octets 127-255 (7F-FF hex)
	In addition, octet 0 (0 hex) should NEVER be used, in either		In addition, octet 0 (0 hex) should NEVER be used, in either
	unencoded or %-encoded form.		unencoded or %-encoded form.
	An URN ends when an octet/character from the excluded character set		An URN ends when an octet/character from the excluded character set
	(<excluded>) is encountered. The character from the excluded		(excluded) is encountered. The character from the excluded character
	character set is NOT part of the URN.		set is NOT part of the URN.
	3. Support of existing legacy naming systems and new naming systems		3. Support of existing legacy naming systems and new naming systems
	Any namespace (existing or newly-devised) that is proposed as an		Any namespace (existing or newly-devised) that is proposed as an
	URN-namespace and fulfills the criteria of URN-namespaces MUST be		URN-namespace and fulfills the criteria of URN-namespaces MUST be
	expressed in this syntax. If names in these namespaces contain		expressed in this syntax. If names in these namespaces contain
	characters other than those defined for the URN character set, they		characters other than those defined for the URN character set, they
	MUST be translated into canonical form as discussed in section 2.2.		MUST be translated into canonical form as discussed in section 2.2.
	4. URN presentation and transport		4. URN presentation and transport
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