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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Obsolete informational reference (is this intentional?): RFC 2141 (Obsoleted by RFC 8141) -- Obsolete informational reference (is this intentional?): RFC 3406 (Obsoleted by RFC 8141) Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 URNBIS P. Saint-Andre, Ed. 3 Internet-Draft Cisco Systems, Inc. 4 Obsoletes: 2141 (if approved) R. Moats 5 Intended status: Standards Track October 13, 2012 6 Expires: April 16, 2013 8 Uniform Resource Name (URN) Syntax 9 draft-saintandre-2141bis-00 11 Abstract 13 A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI) 14 that is intended to serve as a persistent, location-independent 15 resource identifier. The general class of URNs is differentiated 16 from all other URIs through the use of the 'urn' URI scheme. This 17 document defines the canonical syntax for URNs, guidelines for URN 18 namespaces, requirements for URN presentation and transmission, and 19 methods for determining URN equivalence. This document obsoletes RFC 20 2141. 22 Status of this Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on April 16, 2013. 39 Copyright Notice 41 Copyright (c) 2012 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 4. URN Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 3 60 4.1. Namespace Identifier Syntax . . . . . . . . . . . . . . . . 4 61 4.2. Namespace Specific String Syntax . . . . . . . . . . . . . 4 62 5. URN Presentation and Transport . . . . . . . . . . . . . . . . 5 63 6. Lexical Equivalence in URNs . . . . . . . . . . . . . . . . . . 5 64 6.1. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . 5 65 6.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 7. Functional Equivalence in URNs . . . . . . . . . . . . . . . . 6 67 8. Handling of URNs by URI Processors . . . . . . . . . . . . . . 6 68 9. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 69 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 70 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 71 11.1. Normative References . . . . . . . . . . . . . . . . . . . 7 72 11.2. Informative References . . . . . . . . . . . . . . . . . . 7 73 Appendix A. Changes from RFC 2141 . . . . . . . . . . . . . . . . 8 74 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . . 8 75 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 77 1. Introduction 79 A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI) 80 [RFC3986] that is intended to serve as a persistent, location- 81 independent resource identifier. The general class of URNs is 82 differentiated from all other URIs through the use of the 'urn' URI 83 scheme. This document defines the canonical syntax for URNs, 84 guidelines for URN namespaces, requirements for URN presentation and 85 transmission, and methods for determining URN equivalence. 87 URNs were originally defined in [RFC2141]. The goal of this document 88 is to specify URNs with the smallest reasonable set of changes from 89 the original definition while ensuring consistency with the updated 90 specification of URIs in [RFC3986]. If approved, this document will 91 obsolete RFC 2141. 93 The discussion venue for this specification is the mailing list of 94 the URNBIS Working Group; further information can be found at 95 . 97 2. Terminology 99 Many important terms used in this document are defined in the URI 100 specification [RFC3986]. 102 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 103 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 104 "OPTIONAL" in this document are to be interpreted as described in 105 [RFC2119]. 107 3. Requirements 109 The requirements for URNs are specified in [RFC1737]. This document 110 does not modify or update those requirements. 112 4. URN Syntax 114 The syntax for a URN is defined as follows using the Augmented 115 Backus-Naur Form (ABNF) as specified in [RFC5234]. 117 URN = "urn" ":" NID ":" NSS 118 ; 119 ; the URI scheme ("urn") is case-insensitive 120 ; 121 NID = (alphanum) 0*30(ldh) (alphanum) 122 ; 123 ; alphanum is defined in RFC 3986 124 ; 125 ldh = alphanum / "-" 126 NSS = 1*(pchar) 127 ; 128 ; pchar is defined in RFC 3986 129 ; 131 The following sections describe provide additional information about 132 these rules. 134 4.1. Namespace Identifier Syntax 136 The syntax here is slightly more restrictive than what was defined in 137 [RFC2141], since it forbids the hyphen character "-" at the end of a 138 NID. 140 NIDs are case insensitive (e.g., "ISBN" and "isbn" identify the same 141 namespace). 143 4.2. Namespace Specific String Syntax 145 Depending on the rules governing a namespace, names that are valid in 146 a namespace might contain characters that are not allowed in URNs 147 according to the urnchar rule (e.g., characters outside the ASCII 148 range or characters that are reserved in URIs, such as "/", "?", and 149 "#"). Such a string MUST be translated into a conformant NSS before 150 using it as a protocol element or otherwise passing it on to other 151 applications. Translation is done by percent-encoding each 152 disallowed character using the method defined in [RFC3986]. 154 The "%" character is allowed only for the purpose of percent- 155 encoding. 157 If a namespace designates one or more characters conforming to the 158 urnchar rule as having special meaning for that namespace (e.g., "@") 159 and the namespace also uses that character in a literal sense, when 160 used in a literal sense the character MUST be percent-encoded (e.g., 161 "%40"). For related considerations with regard to NID registration, 162 see [RFC3406]. 164 5. URN Presentation and Transport 166 The URN syntax defines the canonical format for URNs. All URN 167 transport and interchanges MUST take place in this format. Further, 168 all URN-aware applications MUST offer the option of displaying URNs 169 in this canonical form to allow for direct transcription (for example 170 by cut and paste techniques). Such applications might support 171 display of URNs in a more human-friendly form and might use a 172 character set that includes characters that are not permitted in URN 173 syntax as defined in this RFC (i.e., when displaying URNs to humans, 174 such applications might replace percent-encoded strings with 175 characters in an extended character set such as Unicode). 177 6. Lexical Equivalence in URNs 179 6.1. Procedure 181 For various purposes such as caching, often it is desirable to 182 determine if two URNs are "the same". This is done by testing for 183 "lexical equivalence". 185 Two URNs are lexically equivalent if they are octet-by-octet equal 186 after the following preprocessing rules: 188 1. normalize the case of the URI scheme "urn" 189 2. normalize the case of the NID 190 3. normalize the case of any percent-encoding 192 Note: Percent-encoded characters MUST NOT be decoded. 194 URN namespaces MAY define additional rules for lexical equivalence, 195 such as case-insensitivity of the NSS (or parts thereof). Such rules 196 MUST always have the effect of eliminating some of the false 197 negatives obtained by the procedure above and MUST NOT result in 198 treating two URNs as not equivalent if the procedure here says they 199 are equivalent. For related considerations with regard to NID 200 registration, see [RFC3406]. 202 6.2. Examples 204 The following URN comparisons highlight the lexical equivalence 205 rules: 207 1. URN:foo:a123,456 208 2. urn:foo:a123,456 209 3. urn:FOO:a123,456 210 4. urn:foo:A123,456 211 5. urn:foo:a123%2C456 212 6. URN:FOO:a123%2c456 214 URNs 1, 2, and 3 are lexically equivalent. URN 4 is not lexically 215 equivalent to any of the other URNs in the above set. URNs 5 and 6 216 are lexically equivalent only to each other. 218 7. Functional Equivalence in URNs 220 Functional equivalence is determined within a given namespace and 221 managed by resolvers for that namespace, and thus is beyond the scope 222 of this document. For related considerations with regard to NID 223 registration, see [RFC3406]. 225 8. Handling of URNs by URI Processors 227 The URN syntax has been defined so that URNs can be used in places 228 where URIs are expected. A resolver that conforms to the URI 229 specification [RFC3986] will extract a scheme of "urn" rather than a 230 scheme value of "urn:". 232 A URN MUST be considered an opaque URI by URI resolvers and passed 233 (with the "urn" scheme) to a URN resolver for resolution. The URN 234 resolver can either be an external resolver that the URI resolver 235 knows of, or it can be functionality built-in to the URI resolver. 237 To minimize user confusion, a URI browser SHOULD display the complete 238 URN (including the "urn" scheme) to ensure that there is no confusion 239 between URN namespace identifiers and URL scheme identifiers. 241 9. Security Considerations 243 This document specifies the syntax for URNs. While some namespaces 244 resolvers may assign special meaning to certain of the characters of 245 the Namespace Specific String, any security consideration resulting 246 from such assignment are outside the scope of this document. For 247 related considerations with regard to NID registration, see 248 [RFC3406]. 250 10. IANA Considerations 252 This section formally registers a URI scheme of 'urn'. 254 [Note to RFC Editor: please change "XXXX" to the number assigned to 255 this document upon publication.] 257 URI Scheme Name: urn 258 Status: permanent 259 URI Scheme Syntax: See Section 4 of RFCXXXX. 260 URI Scheme Semantics: The 'urn' scheme identifies Uniform Resource 261 Names, which are persistent, location-independent resource 262 identifiers. 263 Encoding Considerations: See Section 4.2 of RFCXXXX. 264 Applications/Protocols That Use This URI Scheme Name: Uniform 265 Resource Names are used in a wide variety of applications, 266 including bibliographical reference systems and as names for 267 Extensible Markup Language (XML) namespaces. 268 Interoperability Considerations: There are no known interoperability 269 concerns related to use of the 'urn' URI scheme. 270 Security Considerations: See Section 9 of RFCXXXX. 271 Contact: URNBIS WG [mailto:urn@ietf.org] 272 Author/Change Controller: This scheme is registered under the IETF 273 tree. As such, the IETF maintains change control. 274 References None. 276 11. References 278 11.1. Normative References 280 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 281 Requirement Levels", BCP 14, RFC 2119, March 1997. 283 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 284 Resource Identifier (URI): Generic Syntax", STD 66, 285 RFC 3986, January 2005. 287 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 288 Specifications: ABNF", STD 68, RFC 5234, January 2008. 290 11.2. Informative References 292 [RFC1737] Sollins, K. and L. Masinter, "Functional Requirements for 293 Uniform Resource Names", RFC 1737, December 1994. 295 [RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997. 297 [RFC3406] Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom, 298 "Uniform Resource Names (URN) Namespace Definition 299 Mechanisms", BCP 66, RFC 3406, October 2002. 301 Appendix A. Changes from RFC 2141 303 This document makes the following substantive changes from [RFC2141]: 305 o Disallowed "-" at the end of a NID. 306 o Allowed the "~" and "&" characters in an NSS. 307 o Formally registered 'urn' as a URI scheme. 309 Appendix B. Acknowledgements 311 RFC 2141, which provided the basis for this document, was authored by 312 Ryan Moats. 314 Thanks to Julian Reschke for his corrections to the ABNF. 316 Authors' Addresses 318 Peter Saint-Andre (editor) 319 Cisco Systems, Inc. 320 1899 Wynkoop Street, Suite 600 321 Denver, CO 80202 322 USA 324 Phone: +1-303-308-3282 325 Email: psaintan@cisco.com 327 Ryan Moats