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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 URNBIS P. Saint-Andre 3 Internet-Draft &yet 4 Obsoletes: 2141, 3406 (if approved) J. Klensin 5 Intended status: Standards Track 6 Expires: August 10, 2015 February 6, 2015 8 Uniform Resource Names (URNs) 9 draft-ietf-urnbis-rfc2141bis-urn-09 11 Abstract 13 A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI) 14 that is assigned under the "urn" scheme and a particular URN 15 namespace, typically with the intent that the URN will be a 16 persistent, location-independent resource identifier or abstract 17 designator. With regard to URN syntax, this document defines the 18 canonical syntax for URNs (in a way that is consistent with URI 19 syntax), specifies methods for determining URN equivalence, and 20 discusses URI conformance. With regard to URN namespaces, this 21 document specifies a method for defining a URN namespace and 22 associating it with a namespace identifier, and describes procedures 23 for registering namespace identifiers with the Internet Assigned 24 Numbers Authority (IANA). This document obsoletes both RFC 2141 and 25 RFC 3406. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at http://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on August 10, 2015. 44 Copyright Notice 46 Copyright (c) 2015 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (http://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 This document may contain material from IETF Documents or IETF 60 Contributions published or made publicly available before November 61 10, 2008. The person(s) controlling the copyright in some of this 62 material may not have granted the IETF Trust the right to allow 63 modifications of such material outside the IETF Standards Process. 64 Without obtaining an adequate license from the person(s) controlling 65 the copyright in such materials, this document may not be modified 66 outside the IETF Standards Process, and derivative works of it may 67 not be created outside the IETF Standards Process, except to format 68 it for publication as an RFC or to translate it into languages other 69 than English. 71 Table of Contents 73 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 74 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 75 3. URN Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 4 76 3.1. Namespace Identifier Syntax . . . . . . . . . . . . . . . 5 77 3.2. Namespace Specific String Syntax . . . . . . . . . . . . 5 78 3.3. p-component, q-component, and f-component . . . . . . . . 6 79 4. Equivalence of URNs . . . . . . . . . . . . . . . . . . . . . 7 80 4.1. Procedure . . . . . . . . . . . . . . . . . . . . . . . . 7 81 4.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 8 82 5. URI Conformance . . . . . . . . . . . . . . . . . . . . . . . 9 83 6. URN Namespaces . . . . . . . . . . . . . . . . . . . . . . . 10 84 6.1. Formal Namespaces . . . . . . . . . . . . . . . . . . . . 12 85 6.2. Informal Namespaces . . . . . . . . . . . . . . . . . . . 13 86 7. Defining a URN Namespace . . . . . . . . . . . . . . . . . . 13 87 7.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 14 88 7.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 15 89 7.3. Assignment . . . . . . . . . . . . . . . . . . . . . . . 15 90 7.4. Security and Privacy . . . . . . . . . . . . . . . . . . 16 91 7.5. Resolution . . . . . . . . . . . . . . . . . . . . . . . 16 92 8. Registering a URN Namespace . . . . . . . . . . . . . . . . . 17 93 8.1. Formal Namespaces . . . . . . . . . . . . . . . . . . . . 17 94 8.2. Informal Namespaces . . . . . . . . . . . . . . . . . . . 17 95 9. Guidelines for Designated Experts . . . . . . . . . . . . . . 18 96 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 97 10.1. URI Scheme . . . . . . . . . . . . . . . . . . . . . . . 18 98 10.2. Registration of URN Namespaces . . . . . . . . . . . . . 19 99 11. Security and Privacy Considerations . . . . . . . . . . . . . 19 100 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 101 12.1. Normative References . . . . . . . . . . . . . . . . . . 19 102 12.2. Informative References . . . . . . . . . . . . . . . . . 20 103 Appendix A. Registration Template . . . . . . . . . . . . . . . 22 104 A.1. Namespace ID . . . . . . . . . . . . . . . . . . . . . . 22 105 A.2. Version . . . . . . . . . . . . . . . . . . . . . . . . . 22 106 A.3. Date . . . . . . . . . . . . . . . . . . . . . . . . . . 22 107 A.4. Registrant . . . . . . . . . . . . . . . . . . . . . . . 22 108 A.5. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 22 109 A.6. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 22 110 A.7. Assignment . . . . . . . . . . . . . . . . . . . . . . . 22 111 A.8. Resolution . . . . . . . . . . . . . . . . . . . . . . . 22 112 A.9. Documentation . . . . . . . . . . . . . . . . . . . . . . 23 113 A.10. Revision Information . . . . . . . . . . . . . . . . . . 23 114 Appendix B. Changes from RFC 2141 . . . . . . . . . . . . . . . 23 115 Appendix C. Changes from RFC 3406 . . . . . . . . . . . . . . . 23 116 Appendix D. Contributors . . . . . . . . . . . . . . . . . . . . 23 117 Appendix E. Acknowledgements . . . . . . . . . . . . . . . . . . 24 118 Appendix F. Change log for versions of draft-ietf-urnbis- 119 rfc2141bis-urn . . . . . . . . . . . . . . . . . . . 24 120 F.1. Changes from -08 to -09 . . . . . . . . . . . . . . . . . 24 121 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 123 1. Introduction 125 A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI) 126 [RFC3986] that is assigned under the "urn" scheme and a particular 127 namespace, typically with the intent that the URN will be a 128 persistent, location-independent resource identifier or abstract 129 designator. 131 The assignment of URNs is done by an organization (or, in some cases, 132 according to an algorithm or other automated process) that has been 133 formally delegated a namespace within the "urn" scheme (e.g., a URN 134 in the 'example' namespace [RFC6963] might be of the form 135 "urn:example:foo"). 137 This document rests on two key assumptions: 139 1. Assignment of a URN is a managed process. 141 A string that conforms to the URN syntax is not necessarily a 142 valid URN, because a URN needs to be assigned according to the 143 rules of a particular namespace (in terms of syntax, semantics, 144 and process). 146 2. The space of URN namespaces is itself managed. 148 A string in the namespace identifier slot of the URN syntax is 149 not necessarily a valid URN namespace identifier, because in 150 order to be valid a namespace needs to be defined and registered 151 in accordance with the rules specified in this document. 153 So that information about both URN syntax and URN namespaces is 154 available in one place, this document does the following: 156 1. Defines the canonical syntax for URNs in general (in a way that 157 is consistent with URI syntax), specifies methods for determining 158 URN equivalence, and discusses URI conformance. 160 2. Specifies a method for defining a URN namespace and associating 161 it with a namespace identifier, and describes procedures for 162 registering namespace identifiers with the Internet Assigned 163 Numbers Authority (IANA). 165 For URN syntax and URN namespaces, this document modernizes and 166 replaces the definitions from [RFC2141] and [RFC3406]. These 167 modifications build on the requirements provided in [RFC1737] and 168 many years of experience with URNs, in both cases attempting to make 169 the smallest reasonable set of changes from the previous definitions. 171 This document obsoletes both [RFC2141] and [RFC3406]. 173 2. Terminology 175 Several important terms used in this document are defined in the URI 176 specification [RFC3986]. 178 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 179 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 180 "OPTIONAL" in this document are to be interpreted as described in 181 [RFC2119]. 183 3. URN Syntax 185 The syntax of URNs as provided in [RFC2141] was defined before the 186 updated specification of URIs in [RFC3986]. To ensure consistency 187 with the URI syntax as well as semantic flexibility in the use of 188 URNs within particular applications (see 189 [I-D.ietf-urnbis-semantics-clarif] for further discussion), this 190 specification extends the syntax of URNs to explicitly allow several 191 characters (and thus URI components) that were not allowed by 192 [RFC2141], and also makes several smaller syntax adjustments. 194 As a result, the syntax for a URN is defined as follows using the 195 Augmented Backus-Naur Form (ABNF) as specified in [RFC5234]. Rules 196 not defined below (i.e., alphanum, pchar, path-absolute, query, and 197 fragment) are defined in [RFC3986]. 199 namestring = assigned-name 200 [ p-component ] 201 [ q-component ] 202 [ f-component ] 203 assigned-name = "urn" ":" NID ":" NSS 204 ; the URI scheme ("urn") is case insensitive 205 NID = (alphanum) 0*30(ldh) (alphanum) 206 ldh = alphanum / "-" 207 NSS = 1*(pchar) 208 p-component = "/" path-absolute 209 q-component = "?" query 210 f-component = "#" fragment 212 Note that "?" can be used without %-encoding inside q-components and 213 f-components. 215 The following sections provide additional information about these 216 rules. 218 3.1. Namespace Identifier Syntax 220 The syntax here is slightly more restrictive than what was defined in 221 [RFC2141], since it forbids the character "-" at the end of a NID. 223 NIDs are case insensitive (e.g., "ISBN" and "isbn" are equivalent). 225 3.2. Namespace Specific String Syntax 227 Depending on the rules governing a namespace, names that are valid in 228 a namespace might contain characters that are not allowed in URNs 229 according to the "pchar" rule (e.g., characters outside the ASCII 230 range or characters that are reserved in URIs, such as "/", "?", and 231 "#"). Such a string MUST be translated into a conformant NSS before 232 using it as a protocol element or otherwise passing it on to other 233 applications. Translation is done by percent-encoding each 234 disallowed character using the method defined in Section 2.1 of 235 [RFC3986]. Note that the "%" character is allowed only for the 236 purpose of percent-encoding. 238 In order to make URNs as stable and persistent as possible when 239 protocols evolve and the environment around them changes, namespaces 240 SHOULD NOT allow characters outside the basic Latin repertoire 242 [RFC20] unless the nature of the particular namespace makes such 243 characters necessary. 245 If a namespace designates one or more characters conforming to the 246 "pchar" rule as having special meaning for that namespace (e.g., "@") 247 and the namespace also uses that character in a literal sense, when 248 used in a literal sense the character MUST be percent-encoded (e.g., 249 "%40"). For related considerations with regard to NID registration, 250 see below. 252 3.3. p-component, q-component, and f-component 254 The p-component, q-component, and f-component are optional components 255 that follow the assigned-name. In terms of URI syntax these 256 components are essentially equivalent to the URI "path-absolute", 257 "query", and "fragment" constructions, respectively. However, the 258 URN p-component, q-component, and f-component need not be 259 semantically equivalent to the URI path component, query component, 260 and fragment component; therefore they are called by different names 261 in this specification. 263 Unless specifically defined for a particular namespace after 264 publication of this document, use of these components is disallowed, 265 thereby maintaining strict backward compatibility with namespaces 266 defined in accordance with [RFC2141] and registered in accordance 267 with [RFC3406]. 269 This specification does not define the semantics of the p-component, 270 q-component, and f-component for URNs in general. Instead, 271 additional specifications might establish these matters for URN- 272 related services (such as URN resolution) or for individual URN 273 namespaces (e.g., to handle extended information about the resource 274 identified by a URN). For example, it is possible that the 275 q-component might be used in requests to URN resolution services, or 276 that the f-component might be used to distinguish the integral parts 277 of resources named by URNs in particular namespaces (say, the 278 chapters of a book). However, defining such usage is the 279 responsibility of specifications for URN resolution services, 280 namespace registration requests and specifications for individual 281 namespaces, and other appropriate documentation (such as policy 282 documents governing the management of a given URN namespace). 284 As general guidance that might not apply to all cases, it would be 285 inappropriate for namespaces that do not intend to support resolution 286 services to allow q-components. Namespaces which deal with digital 287 manifestations might be able to support f-components. 289 3.3.1. p-component 291 The only formal restriction placed upon a p-component by this 292 specification is that the syntax SHALL adhere to the "path-absolute" 293 rule from [RFC3986]. The inner syntax of a p-component is to be 294 defined by the specification for a particular namespace or URN- 295 related service. (For example, a namespace specification might 296 define a character such as "~" or "@" as a delimiter inside 297 p-components assigned within that namespace.) 299 As described under Section 4, the p-component SHALL be taken into 300 account when determining URN equivalence. 302 3.3.2. q-component 304 The only formal restriction placed upon a q-component by this 305 specification is that the syntax SHALL adhere to the "query" rule 306 from [RFC3986] (prepended by the "?" character). The inner syntax of 307 a q-component is to be defined by the specification for a particular 308 namespace. (For example, a namespace specification might define a 309 character such as ";" or "=" as a delimiter inside q-components 310 assigned within that namespace.) 312 As described under Section 4, the q-component SHALL NOT be taken into 313 account when determining URN equivalence. 315 3.3.3. f-component 317 The only formal restriction placed upon an f-component by this 318 specification is that the syntax SHALL adhere to the "fragment" rule 319 from [RFC3986] (prepended by the "#" character). The inner syntax of 320 an f-component is to be defined by the specification for a particular 321 namespace. (For example, a namespace specification might define a 322 character such as "&" or "+" as a delimiter inside f-components 323 assigned within that namespace.) 325 As described under Section 4, the f-component SHALL NOT be taken into 326 account when determining URN equivalence. 328 4. Equivalence of URNs 330 4.1. Procedure 332 For various purposes such as caching, often it is desirable to 333 determine if two URNs are "the same". This is done by testing for 334 equivalence (see Section 6.1 of [RFC3986]). 336 Note that [RFC3986] is very flexible about equality comparisons, 337 putting the focus on allowing false negatives and avoiding false 338 positives. If comparisons are made in a scheme-independent way, 339 i.e., as URI comparisons only, URNs that this specification considers 340 equal would be rejected. The discussion below applies when the URI 341 is known to be a URN. 343 Two URNs are equivalent if they are octet-by-octet equal after 344 applying case normalization (as specified in Section 6.2.2.1 of 345 [RFC3986]) to the following constructs: 347 1. the URI scheme "urn" 349 2. the NID 351 3. any percent-encoded characters (see Section 2.1 of the base URI 352 specification [RFC3986]) in the NSS 354 Percent-encoded characters MUST NOT be decoded, i.e., percent- 355 encoding normalization (as specified in Section 6.2.2.2 of [RFC3986]) 356 MUST NOT be applied. 358 If a q-component or f-component (or both) are included in a URN, they 359 MUST be ignored for purposes of determining equivalence. 361 URN namespaces MAY define additional rules for equivalence, such as 362 case-insensitivity of the NSS (or parts thereof). Such rules MUST 363 always have the effect of eliminating some of the false negatives 364 obtained by the procedure above and MUST NOT result in treating two 365 URNs as not equivalent if the procedure here says they are 366 equivalent. For related considerations with regard to NID 367 registration, see below. 369 4.2. Examples 371 The following six URN comparisons (which use the "example" NID 372 defined in [RFC6963]) highlight the equivalence rules: 374 1. URN:example:a123,456 376 2. urn:example:a123,456 378 3. urn:EXAMPLE:a123,456 380 4. urn:example:a123%2C456 382 5. URN:EXAMPLE:a123%2c456 383 6. urn:example:A123,456 385 7. urn:example:a123,456/789 387 8. urn:example:a123,456/abc 389 9. urn:example:a123,456?789 391 10. urn:example:a123,456?abc 393 11. urn:example:a123,456#789 395 12. urn:example:a123,456#abc 397 URNs 1, 2, 3, 9, 10, 11, and 12 are equivalent. URNs 4 and 5 are 398 equivalent only to each other. URNs 6, 7, and 8 are not equivalent 399 to any of the others. 401 5. URI Conformance 403 Because a URN is, syntactically, a URI under the "urn" scheme, in 404 theory a URN can be placed in any protocol slot that allows for a URI 405 (e.g., an XML namespace name [XML-NAMES]). However, this does not 406 imply that, semantically, it always makes sense in practice to place 407 a URN in a given URI protocol slot; in particular, because a URN 408 might not specify the location of a resource or even point indirectly 409 to one, it might not be appropriate to place a URN in a URI protocol 410 slot that points to a resource (examples include the 'href' and 'src' 411 attributes and the element in HTML, as well as the 'xml:base' 412 attribute in XML [XML-BASE]). Ultimately, specifications of where it 413 is appropriate to use URNs, or URNs created within particular URN 414 namespaces, are the responsibility of descriptions of individual URI 415 schemes and contexts; this specification cannot possibly anticipate 416 all of the relevant cases. 418 Despite the fact that URNs are not hierarchical and are not 419 appropriate for use as a base URI (see Section 5.1 of [RFC3986]), the 420 relative resolution algorithm specified in Section 5.2 of [RFC3986] 421 still applies to the "urn" URI scheme; implementers need to be aware, 422 however, that running the algorithm against URNs will lead to results 423 that might be unexpected or not useful. 425 A resolver that conforms to the URI specification [RFC3986] will 426 extract a scheme of "urn" rather than a scheme value of "urn:". 427 A URN MUST be considered an opaque URI by URI resolvers and passed 428 (with the "urn" scheme) to a URN resolver for resolution. The URN 429 resolver can either be an external resolver that the URI resolver 430 knows of, or it can be functionality built into the URI resolver. 432 Note that this requirement MAY impose constraints on the contexts in 433 which URNs are appropriately used; see the previous section. 435 To minimize user confusion, a URI browser SHOULD display the complete 436 URN (including the "urn" scheme and any components) to ensure that 437 there is no confusion between URN namespace identifiers and URI 438 scheme identifiers. For example, a URI beginning with "urn:xmpp:" 439 [RFC4854] is very different from a URI beginning with "xmpp:" 440 [RFC5122]. Similarly, a potential DOI scheme [DOI-URI] is different 441 from, and possibly completely unrelated to, a possible DOI URN 442 namespace. 444 When URNs are transported and exchanged, they MUST be represented in 445 this format. Further, all URN-aware applications MUST offer the 446 option of displaying URNs in this canonical form to allow for direct 447 transcription (for example by cut and paste techniques). Such 448 applications might support display of URNs in a more human-friendly 449 form and might use a character set that includes characters that are 450 not permitted in URN syntax as defined in this specification (e.g., 451 when displaying URNs to humans, such applications might replace 452 percent-encoded strings with characters from an extended character 453 repertoire such as that of [UNICODE]). 455 As mentioned, the assignment of URNs is a managed process, as is the 456 assignment of namespaces themselves. Although design of the URNs to 457 be assigned within a given namespace is ceded by this specification 458 to the namespace owner, doing so in a managed way avoids the problems 459 inherent in unmanaged generation of URIs as described in the 460 recommendations regarding URI design and ownership [RFC7320]. 462 6. URN Namespaces 464 A URN namespace is a collection of identifiers that obey three 465 constraints. Such a namespace is (1) unique, (2) assigned in a 466 consistent way, and (3) assigned according to a common definition. 468 1. The "uniqueness" constraint means that an identifier within the 469 namespace is never assigned to more than one resource and never 470 reassigned to a different resource, even if the identifier itself 471 is deprecated or becomes obsolete. 473 2. The "consistent assignment" constraint means that an identifier 474 within the namespace is assigned by an organization or created in 475 accordance with a process or algorithm that is always followed. 477 3. The "common definition" constraint means that there are clear 478 definitions for the syntax of identifiers within the namespace 479 and for the process of assigning or creating them. 481 A URN namespace is identified by a particular NID in order to ensure 482 the global uniqueness of URNs and, optionally, to provide a cue 483 regarding the structure of URNs assigned within a namespace. 485 With regard to global uniqueness, using different NIDs for different 486 collections of identifiers ensures that no two URNs will be the same 487 for different resources, since each collection is required to 488 uniquely assign each identifier. However, a single resource can have 489 more than one URN assigned to it for different purposes (e.g., some 490 numbers might be valid identifiers in two different identifier 491 systems, where the namespace identifier differentiates between the 492 resulting URNs). Subject to other constraints, such as those imposed 493 by the URI syntax [RFC3986], the rules of the URN scheme are intended 494 to allow preserving the normal and natural form of identifiers 495 specified elsewhere and treated as URN namespaces. 497 With regard to the structure of URNs assigned within a namespace, the 498 development of an identifier structure (and thereby a collection of 499 identifiers) depends on the requirements of the community defining 500 the identifiers, how the identifiers will be assigned and used, etc. 501 These issues are beyond the scope of URN syntax and the general rules 502 for URN namespaces, because they are specific to the community 503 defining a namespace (e.g., the bibliographic and publishing 504 communities in the case of the 'ISBN' and 'ISSN' namespaces, or the 505 developers of extensions to the Extensible Messaging and Presence 506 Protocol in the case of the 'XMPP' namespace). 508 URN namespaces inherit certain rights and responsibilities by the 509 nature of URNs, e.g.: 511 1. They uphold the general principles of a well-managed URN 512 namespace by providing persistent identification of resources and 513 unique assignment of identifier strings. 515 2. They can be registered in global registration services. 517 There are two types of URN namespace: formal and informal. These are 518 distinguished by the expected level of service, the information 519 needed to define the namespace, and the procedures for registration. 520 Because the majority of the namespaces registered so far have been 521 formal, this document concentrates on formal namespaces. 523 Note: [RFC3406] defined a third type of "experimental namespaces", 524 denoted by prefixing the namespace identifier with the string "X-". 525 Consistent with [RFC6648], this specification removes the 526 experimental category. Because experimental namespaces were never 527 registered, removing the experimental category has no impact on the 528 existing registries or future registration procedures. Because they 529 are not registered, strings that refer to existing experimental 530 namespaces are not valid URNs. Truly experimental usages can, of 531 course, employ the 'example' namespace [RFC6963]. 533 6.1. Formal Namespaces 535 A formal namespace provides benefit to some subset of users on the 536 Internet. In particular, it would not make sense for a formal 537 namespace to be used only by a community or network that is not 538 connected to the Internet. For example, it would be inappropriate 539 for a NID to effectively force someone to use a proprietary network 540 or service not open to the general Internet user. The intent is 541 that, while the community of those who might actively use the names 542 assigned within that NID might be small, the potential use of 543 identifiers within that NID is open to any user on the Internet. 544 Formal NIDs might be appropriate even when some aspects are not fully 545 open. For example, a namespace might make use of a fee-based, 546 privately managed, or proprietary registry for assignment of URNs in 547 the namespace. However, it might still benefit some Internet users 548 if the associated services have openly-published access protocols. 550 An organization that will assign URNs within a formal namespace ought 551 to meet the following criteria: 553 1. Organizational stability and the ability to maintain the URN 554 namespace for a long time; absent such evidence, it ought to be 555 clear how the namespace can remain viable if the organization can 556 no longer maintain the namespace. 558 2. Competency in name assignment. This will improve the likelihood 559 of persistence (e.g. to minimize the likelihood of conflicts). 561 3. Commitment to not reassigning existing names and to allowing old 562 names to continue to be valid, even if the owners or assignees of 563 those names are no longer members or customers of that 564 organization. With regard to URN resolution [RFC2276], this does 565 not mean that there needs to be resolution of such names, only 566 that the names will not resolve to false or stale information. 568 A formal namespace establishes a particular NID, subject to the 569 following constraints (above and beyond the syntax rules already 570 specified): 572 1. It MUST NOT be an already-registered NID. 574 2. It MUST NOT start with "urn-" (which is reserved for informal 575 namespaces). 577 3. It MUST be more than two characters long. 579 4. It MUST NOT start with "aa-", where "aa" is any combination of 580 two ASCII letters and the hyphen is followed by something other 581 than another hyphen. 583 5. It MUST NOT start with the string "xn--" or any other string 584 consisting of two letters followed by two hyphens. Those strings 585 are reserved for potential representation of DNS A-labels and 586 similar strings in the future [RFC5890]. 588 All two-letter strings, and all two-letter strings followed by "-" 589 and any sequence of valid NID characters, are reserved for potential 590 use as country-code-based NIDs for eventual national registrations of 591 URN namespaces. The definition and scoping of rules for allocation 592 of responsibility for such country-code-based namespaces is beyond 593 the scope of this document. 595 6.2. Informal Namespaces 597 Informal namespaces are full-fledged URN namespaces, with all the 598 associated rights and responsibilities. Informal namespaces differ 599 from formal namespaces in the process for assigning a NID: for an 600 informal namespace, the registrant does not designate the NID; 601 instead, IANA assigns a NID consisting of the string 'urn-' followed 602 by one or more digits (e.g., "urn-7") where the digits consist of the 603 next available number in the sequence of positive integers assigned 604 to informal namespaces. Thus the syntax of an informal namespace is: 606 InformalNamespaceName = "urn-" Number 607 Number = DigitNonZero 0*Digit 608 DigitNonZero = "1"/ "2" / "3" / "4"/ "5" 609 / "6" / "7" / "8" / "9" 610 Digit = "0" / DigitNonZero 612 The only restrictions on are that it (1) consist strictly of 613 ASCII digits, that it (2) not have leading zeros, and that it (3) not 614 cause the NID to exceed the length limitations defined for the URN 615 syntax. 617 7. Defining a URN Namespace 619 The definition of a formal namespace ought to pay particular 620 attention to: 622 1. The purpose of the namespace. 624 2. The syntax of URNs assigned within the namespace, including 625 whether p-, q-, and/or f-components are allowed. 627 3. The process for assigning URNs within the namespace. 629 4. The security implications of assigning URNs within the namespace 630 and using the assigned URNs. 632 5. Optionally, the process for resolving URNs issued within the 633 namepace. 635 The following sections explain these matters in greater detail. For 636 convenience, a template for defining and registering a URN namespace 637 is provided under Appendix A. This information can be especially 638 helpful to entities that wish to request assignment of a URN in a 639 namespace and to entities that wish to provide URN resolution for a 640 namespace. 642 7.1. Purpose 644 The "Purpose" section of the template describes matters such as: 646 1. The kinds of resources identified by URNs assigned within the 647 namespace. 649 2. Why it is preferable to use URNs rather than some other 650 technology (e.g., separate URI schemes or URIs in existing 651 schemes) and why no existing URN namespace is a good fit. 653 3. The kinds of software applications that can use or resolve the 654 assigned URNs (e.g., by differentiating among disparate 655 namespaces, identifying resources in a persistent fashion, or 656 meaningfully resolving and accessing services associated with the 657 namespace). 659 4. The scope of the namespace (public vs. private, global vs. local 660 to a particular organization, nation, or industry). For example, 661 a namespace claiming to deal in "national identification numbers" 662 ought to have a global scope and address all identity number 663 structures, whereas a URN scheme for a particular national 664 identification number system would need to handle only the 665 structure for that nation's identity numbers. 667 5. How the intended community (and the Internet community at large) 668 will benefit from using or resolving the assigned URNs. 670 7.2. Syntax 672 The "Syntax" section of the template contains: 674 1. A description of the structure of URNs within the namespace, in 675 conformance with the fundamental URN syntax. The structure might 676 be described in terms of a formal definition (e.g., using 677 Augmented BNF for Syntax Specifications (ABNF) as specified in 678 [RFC5234]), an algorithm for generating conformant URNs, or a 679 regular expression for parsing the identifier into components; 680 alternatively, the structure might be opaque. 682 2. Any special character encoding rules for assigned URNs (e.g., 683 which character ought to always be used for single-quotes). 685 3. If p-components, q-components, and/or f-components are allowed 686 for the namespace, a discussion of how they are used. 688 4. Rules for determining equivalence between two identifiers in the 689 namespace. Such rules ought to always have the effect of 690 eliminating false negatives that might otherwise result from 691 comparison. If it is appropriate and helpful, reference can be 692 made to the equivalence rules defined in the URI specification 693 [RFC3986]. Examples of equivalence rules include equivalence 694 between uppercase and lowercase characters in the Namespace 695 Specific String, between hyphenated and non-hyphenated groupings 696 in the identifier string, or between single-quotes and double- 697 quotes. (Note that these are not normative statements for any 698 kind of best practice related to handling of equivalences between 699 characters in general; they are statements limited to one 700 particular namespace only.) 702 5. Any special considerations necessary for conforming with the URN 703 syntax. This is particularly applicable in the case of existing 704 naming systems that are used in the context of URNs. For 705 example, if a namespace is used in contexts other than URNs, it 706 might make use of characters that are reserved in the URN syntax. 707 This section ought to note any such characters, and outline 708 necessary mappings to conform to URN syntax. Normally, this will 709 be handled by percent-encoding the character as specified in the 710 URI specification [RFC3986]. 712 7.3. Assignment 714 The "Assignment" section of the template describes matters such as: 716 1. Mechanisms or authorities for assigning URNs to resources. It 717 ought to make clear whether assignment is completely open (e.g., 718 following a particular procedure such as first-come, first-served 719 (FCFS)), completely closed (e.g., for a private organization), or 720 limited in various ways (e.g., delegated to authorities 721 recognized by a particular organization); if limited, it ought to 722 explain how to become an assigner of identifiers or how to 723 request assignment of identifiers from existing assignment 724 authorities. 726 2. Methods for ensuring that URNs within the namespace are unique. 727 For example, identifiers might be assigned sequentially or in 728 accordance with some well-defined process by a single authority, 729 assignment might be partitioned among delegated authorities that 730 are individually responsible for respecting uniqueness rules, or 731 URNs might be created independently following an algorithm that 732 itself guarantees uniqueness. 734 7.4. Security and Privacy 736 The "Security" section of the template describes any potential issues 737 related to security and privacy with regard to assignment, use, and 738 resolution of identifiers within the namespace. Examples of such 739 issues include: 741 o The consequences of producing false negatives and false positives 742 during comparison for equivalence (see "Issues in Identifier 743 Comparison for Security Purposes" [RFC6943]) 745 o Leakage of private information when identifiers are communicated 746 on the public Internet 748 o The potential for directory harvesting 750 o Various issues discussed in the guidelines for security 751 considerations in RFCs [RFC3552] and the privacy considerations 752 for Internet protocols [RFC6973]. 754 7.5. Resolution 756 The "Resolution" section specifies the rules for resolution of URNs 757 assigned within the namespace. If such URNs are intended to be 758 resolvable, the namespace needs to be registered in a Resolution 759 Discovery System (RDS, see [RFC2276]) such as DDDS. Resolution then 760 proceeds according to standard URI resolution processes, as well as 761 the mechanisms of the RDS. This section ought to list the 762 requirements for becoming a recognized resolver of URNs in the 763 relevant namespace (and being so listed in the RDS registry). 764 Answers might include, but are not limited to: 766 1. The namespace is not listed with an RDS; therefore this section 767 is not applicable. 769 2. Resolution mirroring is completely open, with a mechanism for 770 updating an appropriate RDS. 772 3. Resolution is controlled by entities to which assignment has been 773 delegated. 775 8. Registering a URN Namespace 777 8.1. Formal Namespaces 779 The registration policy for formal namespaces is Expert Review as 780 defined in the "IANA Considerations" document [RFC5226] and in 781 Section 9 below. The key steps for registration of a formal 782 namespace are: 784 1. Fill out the namespace registration template (see Appendix A). 785 This can be done as part of an Internet-Draft or a specification 786 in another series, although that is not necessary. 788 2. Send the completed template to the urn-nid@ietf.org discussion 789 list for review. 791 3. If necessary to address comments received, repeat steps 1 and 2. 793 4. If the designated experts approve the request, the IANA will 794 register the requested NID. 796 A formal namespace registration can be revised by updating the 797 registration template, following the same steps outlined above for 798 new registrations. A revised registration MUST describe differences 799 from prior versions and SHOULD make special note of any relevant 800 changes in the underlying technologies or namespace management 801 processes. 803 8.2. Informal Namespaces 805 The registration policy for informal namespaces is First Come First 806 Served [RFC5226]. The key steps for registration of an informal 807 namespace are: 809 1. Write a completed namespace definition template (see Appendix A). 811 2. Send it to the urn-nid@ietf.org discussion list for feedback. 813 3. Once the review period has expired, send the final template to 814 IANA (via the iana@iana.org email address). 816 An informal namespace registration can be revised by updating the 817 registration template, following the same steps outlined above for 818 new registrations. 820 9. Guidelines for Designated Experts 822 Experience to date with NID registration requests has shown that 823 registrants sometimes do not initially understand some of the 824 subtleties of URN namespaces, and that defining the namespace in the 825 form of a specification enables the registrants to clearly formulate 826 their "contract" with the intended user community. Therefore, 827 although the registration policy for formal namespaces is Expert 828 Review and a stable specification is not strictly required, the 829 designated experts for NID registration requests ought to encourage 830 applicants to provide a stable specification documenting the 831 namespace definition. 833 Naming can be difficult and contentious; the designated experts and 834 applicants are strongly encouraged to work together in a spirit of 835 good faith and mutual understanding to achieve rough consensus on 836 progressing registrations through the process. They are also 837 encouraged to bring additional expertise into the discussion if that 838 would be helpful in adding perspective or otherwise resolving issues. 840 10. IANA Considerations 842 10.1. URI Scheme 844 This section updates the registration of the 'urn' URI scheme in the 845 Permanent URI Registry [URI-Registry] . 847 [Note to RFC Editor: please replace "XXXX" with the number assigned 848 to this document upon publication.] 850 URI Scheme Name: urn 852 Status: permanent 854 URI Scheme Syntax: See Section 3 of [ this document ]. 856 URI Scheme Semantics: The 'urn' scheme identifies Uniform Resource 857 Names, which are persistent, location-independent resource 858 identifiers. 860 Encoding Considerations: See Section 3.2 of [ this document ]. 862 Applications/Protocols That Use This URI Scheme Name: Uniform 863 Resource Names are used in a wide variety of applications, 864 including bibliographic reference systems and as names for 865 Extensible Markup Language (XML) namespaces. 867 Interoperability Considerations: See Section 5 of [ this document ]. 869 Security Considerations: See Section 7.4 and Section 11 of [ this 870 document ]. 872 Contact: URNBIS WG [mailto:urn@ietf.org] 874 Author/Change Controller: This scheme is registered under the IETF 875 tree. As such, the IETF maintains change control. 877 References None. 879 10.2. Registration of URN Namespaces 881 This document outlines the processes for registering URN namespaces, 882 and has implications for the IANA in terms of registries to be 883 maintained. In all cases, the IANA ought to assign the appropriate 884 NID (formal or informal) once the procedures outlined in this 885 document have been completed. 887 11. Security and Privacy Considerations 889 The definition of a URN namespace needs to account for potential 890 security and privacy issues related to assignment, use, and 891 resolution of identifiers within the namespace (e.g., some namespace 892 resolvers might assign special meaning to certain characters in the 893 Namespace Specific String); see Section 7.4 for further discussion. 895 In most cases, URN namespaces provide a way to declare public 896 information. Nominally, these declarations will have a relatively 897 low security profile, however there is always the danger of 898 "spoofing" and providing misinformation. Information in these 899 declarations ought to be taken as advisory. 901 12. References 903 12.1. Normative References 905 [RFC20] Cerf, V., "ASCII format for network interchange", RFC 20, 906 October 1969. 908 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 909 Requirement Levels", BCP 14, RFC 2119, March 1997. 911 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 912 Resource Identifier (URI): Generic Syntax", STD 66, RFC 913 3986, January 2005. 915 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 916 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 917 May 2008. 919 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 920 Specifications: ABNF", STD 68, RFC 5234, January 2008. 922 [URI-Registry] 923 IANA, "Permanent URI Schemes", 924 . 927 12.2. Informative References 929 [I-D.ietf-urnbis-semantics-clarif] 930 Klensin, J., "URN Semantics Clarification", draft-ietf- 931 urnbis-semantics-clarif-00 (work in progress), August 932 2014. 934 [DOI-URI] Paskin, N., Neylon, E., Hammond, T., and S. Sun, "The 935 "doi" URI Scheme for the Digital Object Identifier (DOI)", 936 June 2003, 937 . 939 [RFC1737] Sollins, K. and L. Masinter, "Functional Requirements for 940 Uniform Resource Names", RFC 1737, December 1994. 942 [RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997. 944 [RFC2276] Sollins, K., "Architectural Principles of Uniform Resource 945 Name Resolution", RFC 2276, January 1998. 947 [RFC3406] Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom, 948 "Uniform Resource Names (URN) Namespace Definition 949 Mechanisms", BCP 66, RFC 3406, October 2002. 951 [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC 952 Text on Security Considerations", BCP 72, RFC 3552, July 953 2003. 955 [RFC4854] Saint-Andre, P., "A Uniform Resource Name (URN) Namespace 956 for Extensions to the Extensible Messaging and Presence 957 Protocol (XMPP)", RFC 4854, April 2007. 959 [RFC5122] Saint-Andre, P., "Internationalized Resource Identifiers 960 (IRIs) and Uniform Resource Identifiers (URIs) for the 961 Extensible Messaging and Presence Protocol (XMPP)", RFC 962 5122, February 2008. 964 [RFC5890] Klensin, J., "Internationalized Domain Names for 965 Applications (IDNA): Definitions and Document Framework", 966 RFC 5890, August 2010. 968 [RFC6648] Saint-Andre, P., Crocker, D., and M. Nottingham, 969 "Deprecating the "X-" Prefix and Similar Constructs in 970 Application Protocols", BCP 178, RFC 6648, June 2012. 972 [RFC6943] Thaler, D., "Issues in Identifier Comparison for Security 973 Purposes", RFC 6943, May 2013. 975 [RFC6963] Saint-Andre, P., "A Uniform Resource Name (URN) Namespace 976 for Examples", BCP 183, RFC 6963, May 2013. 978 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 979 Morris, J., Hansen, M., and R. Smith, "Privacy 980 Considerations for Internet Protocols", RFC 6973, July 981 2013. 983 [RFC7320] Nottingham, M., "URI Design and Ownership", BCP 190, RFC 984 7320, July 2014. 986 [UNICODE] The Unicode Consortium, "The Unicode Standard, Version 987 6.3", 2013, 988 . 990 [XML-BASE] 991 Marsh, J. and R. Tobin, "XML Base (Second Edition)", World 992 Wide Web Consortium Recommendation REC-xmlbase-20090128, 993 January 2009, 994 . 996 [XML-NAMES] 997 Thompson, H., Hollander, D., Layman, A., Bray, T., and R. 998 Tobin, "Namespaces in XML 1.0 (Third Edition)", World Wide 999 Web Consortium Recommendation REC-xml-names-20091208, 1000 December 2009, 1001 . 1003 Appendix A. Registration Template 1005 A.1. Namespace ID 1007 Requested of IANA (formal) or assigned by IANA (informal). 1009 A.2. Version 1011 The version of the registration, starting with 1 and incrementing by 1012 1 with each new version. 1014 A.3. Date 1016 The date when the registration is requested of IANA, using the format 1017 YYYY-MM-DD. 1019 A.4. Registrant 1021 The person or organization that has registered the NID, including the 1022 following information: 1024 o The name and address of the registering organization. 1026 o The name and contact information (email, phone number, and/or 1027 postal address) of the designated contact person. 1029 A.5. Purpose 1031 Described under Section 7.1 of this document. 1033 A.6. Syntax 1035 Described under Section 7.2 of this document. Unless the 1036 registration explicitly says otherwise, use of p-, q-, and/or 1037 f-components is not allowed for this namespace. 1039 A.7. Assignment 1041 Described under Section 7.3 of this document. 1043 A.8. Resolution 1045 Described under Section 7.5 of this document. 1047 A.9. Documentation 1049 A pointer to an RFC, a specification published by another standards 1050 development organization, or another stable document that provides 1051 further information about the namespace. 1053 A.10. Revision Information 1055 (Applicable only when earlier registrations have been revised.) 1057 Description of changes from prior version(s). 1059 Appendix B. Changes from RFC 2141 1061 This document makes the following substantive changes from [RFC2141]: 1063 o Allows p-components, q-components, and f-components. 1065 o Disallows "-" at the end of a NID. 1067 o Allows the "~" and "&" characters in an NSS. 1069 o Formally registers 'urn' as a URI scheme. 1071 Appendix C. Changes from RFC 3406 1073 This document makes the following substantive changes from [RFC3406]: 1075 1. Relaxes the registration policy for formal namespaces from "IETF 1076 Review" to "Expert Review" as discussed in Section 8.1 and 1077 Section 9. 1079 2. Removes the category of experimental namespaces, consistent with 1080 [RFC6648]. 1082 3. Simplifies the registration template. 1084 In addition, some of the text has been updated to be consistent with 1085 the definition of Uniform Resource Identifiers (URIs) [RFC3986] and 1086 the processes for registering information with the IANA [RFC5226], as 1087 well as more modern guidance with regard to security issues [RFC3552] 1088 and identifier comparison [RFC6943]. 1090 Appendix D. Contributors 1092 RFC 2141, which provided the basis for the syntax portion of this 1093 document, was authored by Ryan Moats. 1095 RFC 3406, which provided the basis for the namespace portion of this 1096 document, was authored by Leslie Daigle, Dirk-Willem van Gulik, 1097 Renato Iannella, and Patrik Faltstrom. 1099 Their work is gratefully acknowledged. 1101 Appendix E. Acknowledgements 1103 Many thanks to Marc Blanchet, Leslie Daigle, Martin Duerst, Juha 1104 Hakala, Ted Hardie, Alfred Hoenes, Paul Jones, Barry Leiba, Sean 1105 Leonard, Larry Masinter, Keith Moore, Mark Nottingham, Julian 1106 Reschke, Lars Svensson, Dale Worley, and other participants in the 1107 URNBIS WG for their input. Alfred Hoenes in particular edited an 1108 earlier version of this document and served as co-chair of the URNBIS 1109 WG. 1111 Juha Hakala deserves special recognition for his dedication to 1112 successfully completing this work, as do Andrew Newton in his role as 1113 working group chair and Barry Leiba in his role as area director. 1115 Appendix F. Change log for versions of draft-ietf-urnbis-rfc2141bis-urn 1117 [[RFC Editor: please remove this appendix before publication.]] 1119 F.1. Changes from -08 to -09 1121 o Altered the text in Section 5 to reflect list discussions about 1122 the earlier phrasing. Also added DOI example and citation to that 1123 section. 1125 o Clarified the naming rules for formal namespaces and their 1126 relationship to ISO 3166, IDNA, etc., reserved strings. 1128 o Added an explicit statement about use of URNs in various protocols 1129 and contexts to Section 5. 1131 o Clarified that experimental namespace NIDs, which were explicitly 1132 not registered, are not valid URNs (in Section 6. 1134 o Transformed the partial production in Section 6.2 into valid ABNF. 1136 o Added more text about p-/q-/f-components and recommendations about 1137 use. 1139 o Added clarifying note about "?" within q-components and 1140 f-components. 1142 o Added explicit requirement that revisions of existing 1143 registrations document the changes and added a slot for that 1144 description to the template. 1146 o Many small editorial changes and adjustments including adding 1147 additional references and cross-references for clarification. 1149 o Inserted a placeholder for additional examples. 1151 Authors' Addresses 1153 Peter Saint-Andre 1154 &yet 1156 Email: peter@andyet.com 1157 URI: https://andyet.com/ 1159 John C Klensin 1160 1770 Massachusetts Ave, Ste 322 1161 Cambridge, MA 02140 1162 USA 1164 Phone: +1 617 245 1457 1165 Email: john-ietf@jck.com