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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 Filament 4 Obsoletes: 2141, 3406 (if approved) J. Klensin 5 Intended status: Standards Track April 16, 2016 6 Expires: October 18, 2016 8 Uniform Resource Names (URNs) 9 draft-ietf-urnbis-rfc2141bis-urn-16 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, with the intent that the URN will be either a persistent, 16 location-independent resource identifier or in some cases an abstract 17 designator that is persistent but that does not identify a resource. 18 With regard to URN syntax, this document defines the canonical syntax 19 for URNs (in a way that is consistent with URI syntax), specifies 20 methods for determining URN equivalence, and discusses URI 21 conformance. With regard to URN namespaces, this document specifies 22 a method for defining a URN namespace and associating it with a 23 namespace identifier, and describes procedures for registering 24 namespace identifiers with the Internet Assigned Numbers Authority 25 (IANA). This document obsoletes both RFC 2141 and 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 October 18, 2016. 44 Copyright Notice 46 Copyright (c) 2016 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 1.1. Specificity and this Standard . . . . . . . . . . . . . . 5 75 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 76 2. URN Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 6 77 2.1. Namespace Identifier (NID) . . . . . . . . . . . . . . . 7 78 2.2. Namespace Specific String (NSS) . . . . . . . . . . . . . 8 79 2.3. Optional Components . . . . . . . . . . . . . . . . . . . 9 80 2.3.1. q-component . . . . . . . . . . . . . . . . . . . . . 9 81 2.3.2. r-component . . . . . . . . . . . . . . . . . . . . . 10 82 2.3.3. f-component . . . . . . . . . . . . . . . . . . . . . 11 83 3. Equivalence of URNs . . . . . . . . . . . . . . . . . . . . . 12 84 3.1. Procedure . . . . . . . . . . . . . . . . . . . . . . . . 12 85 3.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 13 86 4. URI Conformance . . . . . . . . . . . . . . . . . . . . . . . 15 87 4.1. Use in URI Protocol Slots . . . . . . . . . . . . . . . . 15 88 4.2. Parsing . . . . . . . . . . . . . . . . . . . . . . . . . 15 89 4.3. URNs and Relative References . . . . . . . . . . . . . . 15 90 4.4. Transport and Display . . . . . . . . . . . . . . . . . . 16 91 4.5. URI Design and Ownership . . . . . . . . . . . . . . . . 17 92 5. URN Namespaces . . . . . . . . . . . . . . . . . . . . . . . 17 93 5.1. Formal Namespaces . . . . . . . . . . . . . . . . . . . . 18 94 5.2. Informal Namespaces . . . . . . . . . . . . . . . . . . . 20 95 6. Defining and Registering a URN Namespace . . . . . . . . . . 20 96 6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 20 97 6.2. Registration Policy and Process: Community Registrations 21 98 6.3. Registration Policy and Process: Fast Track for Standards 99 Development Organizations, Scientific Societies, and 100 Similar Bodies . . . . . . . . . . . . . . . . . . . . . 22 101 6.4. Completing the Template . . . . . . . . . . . . . . . . . 23 102 6.4.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . 23 103 6.4.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . 24 104 6.4.3. Assignment . . . . . . . . . . . . . . . . . . . . . 25 105 6.4.4. Security and Privacy . . . . . . . . . . . . . . . . 25 106 6.4.5. Interoperability . . . . . . . . . . . . . . . . . . 26 107 6.4.6. Resolution . . . . . . . . . . . . . . . . . . . . . 26 108 6.4.7. Additional Information . . . . . . . . . . . . . . . 26 109 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 110 7.1. URI Scheme . . . . . . . . . . . . . . . . . . . . . . . 27 111 7.2. Registration of URN Namespaces . . . . . . . . . . . . . 27 112 8. Security and Privacy Considerations . . . . . . . . . . . . . 28 113 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 114 9.1. Normative References . . . . . . . . . . . . . . . . . . 28 115 9.2. Informative References . . . . . . . . . . . . . . . . . 28 116 Appendix A. Registration Template . . . . . . . . . . . . . . . 31 117 Appendix B. Changes from RFC 2141 . . . . . . . . . . . . . . . 32 118 B.1. Syntax changes from RFC 2141 . . . . . . . . . . . . . . 32 119 B.2. Other changes from RFC 2141 . . . . . . . . . . . . . . . 33 120 Appendix C. Changes from RFC 3406 . . . . . . . . . . . . . . . 33 121 Appendix D. Contributors . . . . . . . . . . . . . . . . . . . . 33 122 Appendix E. Acknowledgements . . . . . . . . . . . . . . . . . . 33 123 Appendix F. Change log for versions of draft-ietf-urnbis- 124 rfc2141bis-urn . . . . . . . . . . . . . . . . . . . 34 125 F.1. Changes from -08 to -09 . . . . . . . . . . . . . . . . . 34 126 F.2. Changes from -09 to -10 . . . . . . . . . . . . . . . . . 35 127 F.3. Changes from -10 to -11 . . . . . . . . . . . . . . . . . 35 128 F.4. Changes from -11 to -12 . . . . . . . . . . . . . . . . . 35 129 F.5. Changes from -12 to -13 . . . . . . . . . . . . . . . . . 36 130 F.6. Changes from -13 to -14 . . . . . . . . . . . . . . . . . 36 131 F.7. Changes from -14 to -15 . . . . . . . . . . . . . . . . . 36 132 F.8. Changes from -15 (2016-02-04) to -16 . . . . . . . . . . 37 133 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37 135 1. Introduction 137 A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI) 138 [RFC3986] that is assigned under the "urn" scheme and a particular 139 namespace, with the intent that the URN will be either a persistent, 140 location-independent resource identifier or in some cases an abstract 141 designator that is persistent but that does not identify a resource. 142 A URN namespace is a collection of such identifiers, each of which is 143 (1) unique, (2) assigned in a consistent and managed way, and (3) 144 assigned according to a common definition. (Some URN namespaces 145 create names that exist only as URNs, whereas others create URNs out 146 of names that already exist in other identifier systems, such as 147 ISBNs [RFC3187] and ISSNs [RFC3044].) 149 The assignment of URNs is done by an organization (or, in some cases, 150 according to an algorithm or other automated process) that has been 151 formally delegated a namespace within the "urn" scheme (e.g., a URN 152 in the 'example' namespace [RFC6963] might be of the form 153 "urn:example:foo"). 155 This document rests on two key assumptions: 157 1. Assignment of a URN is a managed process. 159 2. The space of URN namespaces is itself managed. 161 While other URI schemes may allow identifiers to be freely chosen and 162 assigned, such is not the case for URNs. The syntactical correctness 163 of a string starting with "urn:" is not sufficient to make it a URN. 164 In order for the string to be a valid URN, the namespace identifier 165 needs to be registered in accordance with the rules defined here and 166 the remaining parts of the assigned-name portion of the URN needs to 167 be generated in accordance with the rules for the registered 168 namespace. 170 So that information about both URN syntax and URN namespaces is 171 available in one place, this document does the following: 173 1. Defines the canonical syntax for URNs in general (in a way that 174 is consistent with URI syntax), specifies methods for determining 175 URN equivalence, and discusses URI conformance. 177 2. Specifies a method for defining a URN namespace and associating 178 it with a namespace identifier, and describes procedures for 179 registering namespace identifiers with the Internet Assigned 180 Numbers Authority (IANA). 182 For URN syntax and URN namespaces, this document modernizes and 183 replaces the definitions from the original URN syntax [RFC2141] and 184 namespace definition and registration [RFC3406] specifications. 185 These modifications build on the key requirements provided in the 186 original functional description for URN [RFC1737] and many years of 187 experience. In both those original documents and the present one, 188 the intent is to define URNs in a consistent manner so that, wherever 189 practical, the parsing, handling, and resolution of URNs can be 190 independent of the namespace within which a given URN is assigned. 192 Together with input from several key user communities, the history 193 and experiences dictated expansion of the URN definition to support 194 new functionality, including the use of syntax explicitly reserved 195 for future standardization in RFC 2141. All namespaces and URNs that 196 were valid under the earlier specifications remain valid even though 197 it may be useful to update some of them to take advantage of new 198 features. 200 Summaries of changes from RFC 2141 and RFC 3406 appear in Appendix B 201 and Appendix C respectively. This document obsoletes both [RFC2141] 202 and [RFC3406]. While it does not explicitly update or replace 203 [RFC1737] or [RFC2276] the reader who references those documents 204 should be aware that the conceptual model of URNs in this document is 205 slightly different from those older specifications. 207 1.1. Specificity and this Standard 209 To a degree much greater than when URNs were first considered and 210 their uses outlined (Cf. [RFC1737]) issues of persistent identifiers 211 on the Internet involve fundamental design tradeoffs and research 212 questions that are much broader that URNs or the URN approach. Ideal 213 and comprehensive specifications about what should be done or 214 required across the entire range of URNs would require general 215 agreement about those issues and their resolution. While some of 216 them were introduced by the Internet or computer-age approaches to 217 character encodings and data abstraction, others predate the Internet 218 and computer systems by centuries; there is unlikely to be agreement 219 about comprehensive solutions in the near future. 221 Among these general issues, one that is specific to URNs is the 222 fairly abstract topic of "resolution", discussed in Section 1.2, 223 Section 2.3.2, and elsewhere below. While it is possible to define 224 the relationships quite precisely for a URN that resolves to a URL 225 that, in turn, resolves (or locates) to a single target document or 226 similar resource, that is only one special case albeit an important 227 one. URNs (either individually or entire namespaces as defined 228 below) that do not resolve to URLs at all or that resolve to metadata 229 or non-Internet objects are among URN use cases explicitly permitted 230 by this specification; each leaves the concept of "resolution" 231 somewhat more abstract and difficult than the simple case of 232 resolution to a URL. 234 A similar set of issues arises for character sets and encodings. 235 URNs, especially URNs that will be used as user-facing identifiers, 236 should be convenient to use in local languages and writing systems, 237 easily specified with a wide range of keyboards and local 238 conventions, and unambiguous. There are tradeoffs among those goals 239 and it is impossible at present to see how a simple and readily- 240 understandable set of rules could be developed that would be optimal, 241 or even reasonable, for all URNs. The discussion in Section 2.2 242 defines an overall framework that should make generalized parsing and 243 processing possible, but also makes recommendations about rules for 244 individual namespaces. 246 This specification consequently contains some requirements and 247 flexibility that would not be present in a more perfect world but 248 that are necessary in order to allow producing any consensus 249 specification at all rather than just giving up on URNs going 250 forward. 252 1.2. Terminology 254 This document uses the terms "resolution" and "resolver" in roughly 255 the sense in which they were used in the original discussion of 256 architectural principles for URNs [RFC2276], i.e., "resolution" is 257 the act of supplying services related to the identified resource, 258 such as translating the persistent name into one or more current 259 locators for the resource, delivering metadata about the resource in 260 an appropriate format, or even delivering a document object from a 261 convenient source without requiring further intermediaries. At the 262 time of this writing, resolution services are described in [RFC2483]. 263 In order to underline the difference between the names and locators, 264 this document uses the term Uniform Resource Locator (URL), rather 265 than the generic term Uniform Resource Identifier (URI), to refer to 266 locators; see also Section 1.1.3 of [RFC3986]. 268 If there are or will be resolution services available for a URN, this 269 document calls the URN a "resource identifier" in roughly the sense 270 that term is used in [RFC3986]. If there is no intention to provide 271 any resolution services, and the distinction is important, this 272 document calls the URN an "abstract designator". 274 Several other important terms used in this document, including some 275 "normalization" operations that are not part of the Unicode Standard 276 [UNICODE], are defined in the URI specification [RFC3986]. 278 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 279 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 280 "OPTIONAL" in this document are to be interpreted as described in 281 [RFC2119]. 283 2. URN Syntax 285 As discussed above, the syntax for URNs in this specification allows 286 significantly more functionality than was the case in the earlier 287 specifications. It is also harmonized with the general URI syntax 289 [RFC3986]. That syntax definition was completed after the earlier 290 URN specifications. 292 However, this specification does not extend the URN syntax to allow 293 direct use of characters outside the ASCII range [RFC20]. That 294 prohibition implies that any such characters need to be percent- 295 encoded as described in Section 2.1 of the URI specification 296 [RFC3986]. 298 The basic syntax for a URN is defined using the Augmented Backus-Naur 299 Form (ABNF) as specified in [RFC5234]. Rules not defined here 300 (specifically: alphanum, fragment, and pchar) are defined as part of 301 the URI syntax [RFC3986] and used here to point out the syntactic 302 relationship with the terms used there. The definitions of some of 303 the terms used below are not complete; additional restrictions are 304 imposed sections of the document that are specific to those terms. 306 namestring = assigned-name 307 [ rq-components ] 308 [ "#" f-component ] 309 assigned-name = "urn" ":" NID ":" NSS 310 NID = (alphanum) 0*30(ldh) (alphanum) 311 ldh = alphanum / "-" 312 NSS = pchar *(pchar / "/") 313 rq-components = ( "?=" q-component 314 [ "?+" r-component ] ) / 315 ( "?+" r-component 316 [ "?=" q-component ] ) 317 q-component = pchar *( pchar / "/" / "?" ) 318 r-component = pchar *( pchar / "/" / "?" ) 319 f-component = fragment 321 The question mark character "?" can be used without percent-encoding 322 inside q-components, r-components, and f-components. Other than 323 inside those components a "?" that is not immediately followed by "=" 324 or "+" is not defined for URNs and SHOULD be treated as a syntax 325 error by URN-specific parsers and other processors. 327 The following sections provide additional information about the 328 syntactic elements of URNs. 330 2.1. Namespace Identifier (NID) 332 Namespace Identifiers (NIDs) are case insensitive (e.g., "ISBN" and 333 "isbn" are equivalent). 335 Characters outside the ASCII range [RFC20] are not permitted in NIDs, 336 and no encoding mechanism for such characters is supported. 338 Section 5.1 and Section 5.2 impose additional constraints on the 339 strings that can be used as NIDs, i.e., the syntax shown above is not 340 comprehensive. 342 2.2. Namespace Specific String (NSS) 344 The namespace specific string (NSS) is a unique identifier within a 345 namespace that is assigned and managed in a consistent way and that 346 conforms to the definition of the relevant namespace. The 347 combination of the NID (unique across the entire "urn" scheme) and 348 the NSS (unique within the namespace) ensures that the resulting URN 349 is a globally unique URI. 351 The NSS specified in this document allows characters not permitted by 352 earlier specifications (see Appendix B. In particular, the "/" 353 character, which is now allowed, effectively makes it possible to 354 encapsulate hierarchical identifiers from other naming systems. For 355 instance, consider the hypothetical example of a hierarchical naming 356 system in which the identifiers take the form of a sequence of 357 numbers separated by the "/" character, such as "1/406/47452/2". If 358 the naming authority for such identifiers were to use URNs, it would 359 be natural to place the existing identifiers in the NSS, resulting in 360 URNs such as "urn:example:1/406/47452/2". 362 The changes to the syntax for the NSS do not modify the encoding 363 rules for URN namespaces that were defined in accordance with 364 [RFC2141]. If any such URN namespace that is used outside of the URN 365 context (i.e., as a standalone, non-embedded, identifier space) also 366 allows the use of "/", "~", or "&" in the native form within that 367 identifier space, then the encoding rules for that namespace are not 368 changed by this specification. 370 Depending on the rules governing a namespace, strings that are valid 371 in an NSS associated with that namespace might contain characters 372 that are not allowed by the "pchar" production referenced above 373 (e.g., characters outside the ASCII range or, consistent with the 374 restrictions in RFC 3986, the characters "/", "?", "#", "[", and 375 "]"). While such a string might be a valid name, it is not a valid 376 URN until it has been translated into a conformant NSS. In the case 377 of URNs that are formed from names that exist separately in a 378 standalone identifier space, translation of an identifier from its 379 "native" format to URN format is accomplished by using the 380 canonicalization and encoding methods defined for that URN namespace. 381 Software that is not aware of those namespace-specific 382 canonicalization and encoding rules MUST NOT construct URNs from the 383 names in the standalone identifier space. 385 In particular, with regard to characters outside the ASCII range, 386 URNs that appear in protocols or that are passed between systems MUST 387 use only Unicode characters encoded in UTF-8 and further encoded as 388 required by RFC 3986. To the extent feasible consistent with the 389 requirements of identifiers defined and standardized elsewhere and 390 the principles discussed in Section 1.1, strings SHOULD be restricted 391 to either ASCII letters and digits or to the characters and syntax of 392 some widely-used identifier model such as those of IDNA [RFC5890], 393 PRECIS [RFC7613], or the Unicode Identifier and Pattern Syntax spec 394 [UAX31]. 396 In order to make URNs as stable and persistent as possible when 397 protocols evolve and the environment around them changes, namespaces 398 SHOULD NOT allow characters outside the basic Latin repertoire 399 [RFC20] unless the nature of the particular namespace makes such 400 characters necessary. 402 2.3. Optional Components 404 This specification includes three optional components in the URN 405 syntax. They are known as q-component, r-component, and f-component 406 and are described in more detail below. Because this specification 407 focuses almost exclusively on URN syntax, it does not define detailed 408 semantics of these components for URNs in general. However, each of 409 these components has a distinct role that is independent of the URN 410 and its namespace. It is intended that clients will be able to 411 handle these components uniformly for all URNs. These components MAY 412 be used with URNs from existing namespaces, whether or not a 413 namespace explicitly supports them. However, consistent with the 414 approach taken in RFC 3986, the behavior of a URN that contains 415 components that are undefined or meaningless for a particular 416 namespace or resource is not defined. The following sections 417 describe these optional components and their interpretation in 418 greater detail. 420 2.3.1. q-component 422 The q-component is intended for passing parameters to either the 423 named resource or a system that can supply the requested service, for 424 interpretation by that resource or system. (By contrast, passing 425 parameters to URN resolution services is handled by r-components as 426 described in the next section.) 428 The URN q-component has the same syntax as the URI query component, 429 but is introduced by "?=", not the "?" alone. If a URN resolves to a 430 URL, the q-component from the URN is copied verbatim to the query 431 component of the URL. If the URN does not resolve to a URL (i.e., is 432 an abstract designator or resolves directly to an object or a non-URL 433 resource designator), the interpretation of the q-component is 434 undefined by this specification. Thus, for URNs which may be 435 resolved to a URL, the semantics of q-component are identical to 436 those for queries to the resource located via that URL. 438 For the sake of consistency with RFC 3986, neither the general syntax 439 nor the semantics of q-components are defined by, or dependent on, 440 the namespace of the URN. In parallel with RFC 3896, specifics of 441 syntax and semantics, e.g., which keywords or terms are meaningful, 442 of course may depend on a particular namespace or even a particular 443 resource. 445 The sequence "?=" begins the q-component. The q-component ends with 446 a "?+" sequence (which begins an r-component) or a "#" character 447 (number sign, which begins an f-component). If neither of those 448 appear, the q-component continues to the end of the URN. The 449 characters slash ("/") and question mark ("?") may represent data 450 within the q-component. Note that characters outside the ASCII range 451 [RFC20] MUST be percent-encoded using the method defined in 452 Section 2.1 of the generic URI specification [RFC3986]. 454 As described in Section 3, the q-component SHALL NOT be taken into 455 account when determining URN equivalence. 457 Namespaces and associated information placement in syntax SHOULD be 458 designed to avoid any need for a resolution service to consider the 459 q-component. Namespace-specific and more generic resolution systems 460 MUST NOT require that q-component information be passed to them for 461 processing. 463 Consider the hypothetical example of passing parameters to an 464 application that returns weather reports from different regions or 465 for different time periods. This could perhaps be accomplished by 466 specifying latitude and longitude coordinates and datetimes in the 467 URN's q-component, resulting in URNs such as the following. 469 urn:example:weather?=op=map&lat=39.56 470 &lon=-104.85&datetime=1969-07-21T02:56:15Z 472 2.3.2. r-component 474 The r-component is intended for passing parameters to URN resolution 475 services (taken broadly, see Section 1.1) and interpreted by those 476 services. (By contrast, passing parameters to the resources 477 identified by a URN, or to applications that manage such resources, 478 is handled by q-components as described in the previous section.) 479 The URN r-component has no syntactic equivalent in URLs. 481 The sequence "?+" begins the r-component. The r-component ends with 482 a "?=" sequence (which begins a q-component) or a "#" character 483 (number sign, which begins an f-component). If neither of those 484 appear, the r-component continues to the end of the URN. Note that 485 characters outside the ASCII range [RFC20] MUST be percent-encoded 486 using the method defined in Section 2.1 of the generic URI 487 specification [RFC3986]. 489 As described under Section 3, the r-component SHALL NOT be taken into 490 account when determining URN equivalence. However, the r-component 491 SHALL be supplied along with the URN when presenting a request to a 492 URN resolution service. 494 This document defines only the syntax of the r-component and reserves 495 it for future use. The exact semantics of the r-component and its 496 use in URN resolution protocols are a matter for potential 497 standardization in separate specifications, presumably including 498 specifications that define conventions and a registry for resolution 499 service identifiers. 501 Consider the hypothetical example of passing parameters to a 502 resolution service (say, an ISO alpha-2 country code [ISO3166-1] in 503 order to scope down the preferred country in which to search for a 504 physical copy of a book). This could perhaps be accomplished by 505 specifying the country code in the r-component, resulting in URNs 506 such as: 508 urn:example:foo-bar-baz-qux?+CCResolve: cc=uk 510 While the above should serve as a general explanation and 511 illustration of the intent for r-components, there are many 512 unresolved issues with them, including their relationship to 513 resolution mechanisms associated with the particular NID and 514 namespace at registration time. Thus r-components SHOULD NOT be used 515 for actual URNs until additional development and standardization work 516 is complete, including specification of any necessary registration 517 mechanisms. 519 2.3.3. f-component 521 The f-component is intended to be interpreted by the client as a 522 specification for a location within, or region of, the named 523 resource. 525 The URN f-component has the same syntax as the URI fragment 526 component. If a URN containing an f-component resolves to a single 527 URL associated with the named resource, the f-component from the URN 528 can be applied (usually by the client) verbatim as the fragment of 529 that URL. If the URN does not resolve to a URL (e.g., is an abstract 530 designator), the interpretation of the f-component is undefined by 531 this specification. Thus, for URNs which may be resolved to a URL, 532 the semantics of f-components are identical to those of fragments for 533 that resource. 535 For the sake of consistency with RFC 3986, neither the general syntax 536 nor the semantics of f-components are defined by, or dependent on, 537 the namespace of the URN. In parallel with RFC 3896, specifics of 538 syntax and semantics, e.g., which keywords or terms are meaningful, 539 of course may depend on a particular namespace or even a particular 540 resource. 542 The f-component is indicated by the presence of a number sign ("#") 543 character and terminated by the end of the URI. Any characters 544 outside the ASCII range [RFC20] that appear in the f-component MUST 545 be percent-encoded using the method defined in Section 2.1 of the 546 generic URI specification [RFC3986]. 548 As described under Section 3, the f-component SHALL NOT be taken into 549 account when determining URN equivalence. 551 Clients SHOULD NOT pass f-components to resolution services unless 552 those services also perform object retrieval and interpretation 553 functions. 555 The f-component is primarily intended to distinguish the constituent 556 parts of resources named by URNs. Thus, for URNs that resolve to 557 URLs of the named resources, the semantics of an f-component are 558 defined by the media type of those resources, not by the namespace. 560 Consider the hypothetical example of obtaining resources that are 561 part of a larger entity (say, the chapters of a book). Each part 562 could be specified in the f-component, resulting in URNs such as: 564 urn:example:foo-bar-baz-qux#somepart 566 3. Equivalence of URNs 568 3.1. Procedure 570 For various purposes such as caching, it is often desirable to 571 determine if two URNs are "the same". This is done by testing for 572 equivalence (see Section 6.1 of [RFC3986]). 574 The generic URI specification [RFC3986] is very flexible about 575 equality comparisons, putting the focus on allowing false negatives 576 and avoiding false positives. If comparisons are made in a scheme- 577 independent way, i.e., as URI comparisons only, URNs that this 578 specification considers equal would be rejected. The discussion 579 below applies when the URIs involved are known to be URNs. 581 Two URNs are equivalent if their portions are octet- 582 by-octet equal after applying case normalization (as specified in 583 Section 6.2.2.1 of [RFC3986]) to the following constructs: 585 1. the URI scheme "urn", by conversion to lower case 587 2. the NID, by conversion to lower case 589 3. any percent-encoded characters in the NSS (that is, all character 590 triplets that match the production found in 591 Section 2.1 of the base URI specification [RFC3986]), by 592 conversion to upper case for the digits A-F. 594 Percent-encoded characters MUST NOT be decoded, i.e., percent- 595 encoding normalization (as specified in Section 6.2.2.2 of [RFC3986]) 596 MUST NOT be applied as part of the comparison process. 598 If a q-component, r-component, or f-component (or any combination 599 thereof) are included in a URN, they MUST be ignored for purposes of 600 determining equivalence. 602 URN namespace definitions MAY include additional rules for 603 equivalence, such as case-insensitivity of the NSS (or parts 604 thereof). Such rules MUST always have the effect of eliminating some 605 of the false negatives obtained by the procedure above and MUST NOT 606 result in treating two URNs as not equivalent if the procedure here 607 says they are equivalent. For related considerations with regard to 608 NID registration, see below. 610 3.2. Examples 612 This section shows a variety of URNs (using the "example" NID defined 613 in [RFC6963]) that highlight the equivalence rules. 615 First, because the scheme and NID are case-insensitive, the following 616 URNs are equivalent to each other: 618 o urn:example:a123,z456 620 o URN:example:a123,z456 621 o urn:EXAMPLE:a123,z456 623 Second, because the q-component and f-component are not taken into 624 account for purposes of testing equivalence, the following URNs are 625 equivalent to the first three examples above: 627 o urn:example:a123,z456?=abc 629 o urn:example:a123,z456#789 631 o urn:example:a123,z456#abc 633 Third, because the "/" character (and anything that follows it) in 634 the NSS is taken into account for purposes of equivalence, the 635 following URNs are not equivalent to each other or to the preceding 636 URNs: 638 o urn:example:a123,z456/foo 640 o urn:example:a123,z456/bar 642 o urn:example:a123,z456/baz 644 Fourth, because of percent-encoding, the following URNs are 645 equivalent only to each other (although %2C is the percent-encoded 646 transformation of "," from the previous examples, such sequences are 647 not decoded for purposes of testing equivalence): 649 o urn:example:a123%2Cz456 651 o URN:EXAMPLE:a123%2cz456 653 Fifth, because characters other than percent-encoded sequences in the 654 NSS are treated in a case-sensitive manner (unless otherwise 655 specified for the namespace in question), the following URNs are not 656 equivalent to the first three URNs: 658 o urn:example:A123,z456 660 o urn:example:a123,Z456 662 Sixth, on casual visual inspection of a URN presented in a human- 663 oriented interface the following URN might appear the same as the 664 first three URNs (because U+0430 CYRILLIC SMALL LETTER A can be 665 confused with U+0061 LATIN SMALL LETTER A), but it is not equivalent: 667 o urn:example:%D0%B0123,z456 669 4. URI Conformance 671 4.1. Use in URI Protocol Slots 673 Because a URN is, syntactically, a URI under the "urn" scheme, in 674 theory a URN can be placed in any protocol slot that allows for a URI 675 (e.g., the 'href' and 'src' attributes in HTML, the element 676 in HTML, the 'xml:base' attribute in XML [XML-BASE], and the 'xmlns' 677 attribute in XML for XML namespace names [XML-NAMES]). 679 However, this does not imply that, semantically, it always makes 680 sense in practice to place a URN in a given URI protocol slot; in 681 particular, because a URN might not specify the location of a 682 resource or even point indirectly to one, it might not be appropriate 683 to place a URN in a URI protocol slot that points to a resource 684 (e.g., the aforementioned 'href' and 'src' attributes). 686 Ultimately, guidelines regarding when it is appropriate to use URIs 687 under the "urn" scheme (or any other scheme) are the responsibility 688 of specifications for individual URI protocol slots (e.g., the 689 specification for the 'xml:base' attribute in XML might recommend 690 that it is inappropriate to use URNs in that protocol slot). This 691 specification cannot possibly anticipate all of the relevant cases, 692 and it is not the place of this specification to require or restrict 693 usage for individual protocol slots. 695 4.2. Parsing 697 In part because of the separation of URN semantics from more general 698 URI syntax [I-D.ietf-urnbis-semantics-clarif], generic URI processors 699 need to pay special attention to the parsing and analysis rules of 700 RFC 3986 and, in particular, must treat the URI as opaque unless the 701 scheme and its requirements are recognized. In the latter case, such 702 processors may be in a position to invoke scheme-appropriate 703 processing such as by a URN resolver. The URN resolver can either be 704 an external resolver that the URI resolver knows of, or it can be 705 functionality built into the URI resolver. Note that this 706 requirement might impose constraints on the contexts in which URNs 707 are appropriately used; see Section 4.1. 709 4.3. URNs and Relative References 711 Section 5.2 of [RFC3986] describes an algorithm for converting a URI 712 reference that might be relative to a given base URI into "parsed 713 components" of the target of that reference, which can then be 714 recomposed per RFC 3986 Section 5.3 into a target URI. This 715 algorithm cannot be applied directly to URNs because their syntax 716 does not support the necessary path components. Whenever a URN 717 resolves to a URL which may be used to access the resource, there is 718 a more specific interpretation of q-component and f-component: the 719 q-component is copied verbatim to the query portion of the URL (if 720 that URL scheme supports query), and the f-component is copied 721 verbatim to the fragment portion of the URL. Even though the notion 722 of a URN as a "persistent", "permanent" identifier does not reconcile 723 easily with relative referencing, resources named with URNs may 724 contain relative references that do not apply to the URN itself. 726 Given the foregoing, a relative reference SHOULD NOT be evaluated 727 directly with respect to a URN. Instead, a relative reference SHOULD 728 be evaluated indirectly with respect to one of the following: 730 1. a base URI (other than a URN) declared by the resource itself; or 732 2. a base URI (other than a URN) obtained through the URN resolution 733 process; or 735 3. the URL of the resource as obtained through the URN resolution 736 process 738 (Case 2 permits the resolution process to explicitly supply a base 739 URI if the resource content is supplied directly by the resolution 740 service rather than via an intermediate "location" URI.) 742 If no such base URI exists, use of a relative reference with respect 743 to a URN is an error. Client behavior in this case is undefined. 745 Resolution services SHOULD ensure that a base URI is supplied any 746 time they provide resource content directly to a client. 748 4.4. Transport and Display 750 When URNs are transported and exchanged, they MUST be represented in 751 the format defined herein. Further, all URN-aware applications MUST 752 offer the option of displaying URNs in this canonical form to allow 753 for direct transcription (for example by cut-and-paste techniques). 754 Such applications might support display of URNs in a more human- 755 friendly form and might use a character set that includes characters 756 that are not permitted in URN syntax as defined in this specification 757 (e.g., when displaying URNs to humans, such applications might 758 replace percent-encoded strings with characters from an extended 759 character repertoire such as Unicode [UNICODE]). 761 To minimize user confusion, a URI browser SHOULD display the complete 762 URN (including the "urn" scheme and any components) to ensure that 763 there is no confusion between URN namespace identifiers and URI 764 scheme identifiers. For example, a URI beginning with "urn:xmpp:" 766 [RFC4854] is very different from a URI beginning with "xmpp:" 767 [RFC5122]. Similarly, a potential DOI URI scheme [DOI-URI] is 768 different from, and possibly completely unrelated to, a possible DOI 769 URN namespace. 771 4.5. URI Design and Ownership 773 As mentioned, the assignment of URNs is a managed process, as is the 774 assignment of namespaces themselves. Although design of the URNs to 775 be assigned within a given namespace is ceded by this specification 776 to the namespace owner, doing so in a managed way avoids the problems 777 inherent in unmanaged generation of URIs as described in the 778 recommendations regarding URI design and ownership [RFC7320]. 780 5. URN Namespaces 782 A URN namespace is a collection of identifiers that obey three 783 constraints: each identifier is (1) unique, (2) assigned in a 784 consistent way, and (3) assigned according to a common definition. 786 1. The "uniqueness" constraint means that an identifier within the 787 namespace is never assigned to more than one resource and never 788 reassigned to a different resource (for the kind of "resource" 789 identified by URNs assigned within the namespace). This holds 790 true even if the identifier itself is deprecated or becomes 791 obsolete. 793 2. The "consistent assignment" constraint means that an identifier 794 within the namespace is assigned by an organization or created in 795 accordance with a process or algorithm that is always followed. 797 3. The "common definition" constraint means that there are clear 798 definitions for the syntax of identifiers within the namespace 799 and for the process of assigning or creating them. 801 A URN namespace is identified by a particular NID in order to ensure 802 the global uniqueness of URNs and, optionally, to provide a cue 803 regarding the structure of URNs assigned within a namespace. 805 With regard to global uniqueness, using different NIDs for different 806 collections of identifiers ensures that no two URNs will be the same 807 for different resources, since each collection is required to 808 uniquely assign each identifier. However, a single resource MAY have 809 more than one URN assigned to it, either in the same namespace (if 810 the namespace permits it) or in different namespaces, and either for 811 similar purposes or different purposes. (For example, if a publisher 812 assigns an ISBN to an electronic publication and that publication is 813 later incorporated into a digital long term archive operated by a 814 national library, the library might assign the publication a NBN, 815 resulting in two URNs referring to the same book.) Subject to other 816 constraints, such as those imposed by the URI syntax [RFC3986], the 817 rules of the URN scheme are intended to allow preserving the normal 818 and natural form of identifiers specified elsewhere when they are 819 treated as URN namespaces. 821 With regard to the structure of URNs assigned within a namespace, the 822 development of an identifier structure (and thereby a collection of 823 identifiers) depends on the requirements of the community defining 824 the identifiers, how the identifiers will be assigned and used, etc. 825 These issues are beyond the scope of URN syntax and the general rules 826 for URN namespaces, because they are specific to the community 827 defining a namespace (e.g., the bibliographic and publishing 828 communities in the case of the 'ISBN' and 'ISSN' namespaces, or the 829 developers of extensions to the Extensible Messaging and Presence 830 Protocol in the case of the 'XMPP' namespace). 832 URN namespaces inherit certain rights and responsibilities by the 833 nature of URNs, e.g.: 835 1. They uphold the general principles of a well-managed URN 836 namespace by providing persistent identification of resources and 837 unique assignment of identifier strings in accordance with a 838 common definition. 840 2. Optionally, they can be registered in global registration 841 services such as those described in [RFC2483]. 843 There are two types of URN namespace: formal and informal. These are 844 distinguished by the expected level of service, the information 845 needed to define the namespace, and the procedures for registration. 846 Because the majority of the namespaces registered so far have been 847 formal, this document concentrates on formal namespaces. 849 5.1. Formal Namespaces 851 A formal namespace provides benefit to some subset of users on the 852 Internet. In particular, it would not make sense for a formal 853 namespace to be used only by a community or network that is not 854 connected to the Internet. For example, it would be inappropriate 855 for a NID to effectively force someone to use a proprietary network 856 or service not open to the general Internet user. The intent is 857 that, while the community of those who might actively use the names 858 assigned within that NID might be small, the potential use of 859 identifiers within that NID is open to any user on the Internet. 860 Formal NIDs might be appropriate even when some aspects are not fully 861 open. For example, a namespace might make use of a fee-based, 862 privately managed, or proprietary registry for assignment of URNs in 863 the namespace. However, it might still benefit some Internet users 864 if the associated services have openly-published identifiers. 866 An organization that will assign URNs within a formal namespace 867 SHOULD meet the following criteria: 869 1. Organizational stability and the ability to maintain the URN 870 namespace for a long time; absent such evidence, it ought to be 871 clear how the namespace can remain viable if the organization can 872 no longer maintain the namespace. 874 2. Competency in name assignment. This will improve the likelihood 875 of persistence (e.g. to minimize the likelihood of conflicts). 877 3. Commitment to not reassigning existing names and to allowing old 878 names to continue to be valid (e.g., if the assignee of a name is 879 no longer a member or customer of the assigning organization, if 880 various information about the assignee or named entity happens to 881 change, or even if the assignee or the named entity itself is no 882 longer in existence; in all these cases, the name is still 883 valid). 885 A formal namespace establishes a particular NID, subject to the 886 following constraints (above and beyond the syntax rules already 887 specified): 889 1. It MUST NOT be an already-registered NID. 891 2. It MUST NOT start with "urn-" (which is reserved for informal 892 namespaces). 894 3. It MUST be more than two characters long. 896 4. It MUST NOT start with ALPHA ALPHA "-", i.e., any string 897 consisting of two letters followed by one hyphen. 899 5. It MUST NOT start with the string "xn--" or any other string 900 consisting of two letters followed by two hyphens. Such strings 901 are reserved for potential representation of DNS A-labels and 902 similar strings in the future [RFC5890]. 904 6. It MUST NOT start with the string "X-" so that it will not be 905 confused with or conflict any experimental namespace previously 906 permitted by [RFC3406]. 908 All two-letter strings, and all two-letter strings followed by "-" 909 and any sequence of valid NID characters, are reserved for potential 910 use as NIDs based on ISO alpha-2 country codes [ISO3166-1] for 911 eventual national registrations of URN namespaces. The definition 912 and scoping of rules for allocation of responsibility for such 913 country-code-based namespaces is beyond the scope of this document. 915 Applicants and reviewers considering new NIDs should also be aware 916 that they may be considered as names with semantic implications and 917 hence a source of conflict. Particular attention should be paid to 918 strings that might be construed as names of, or registered under the 919 authority of, countries (including ISO 3166-1 alpha-3 codes) and to 920 strings that might imply association with existing URI schemes, 921 identifier systems, or trademarks. However, in line with traditional 922 policies, disputes about "ownership" of particular strings are 923 disagreements among the parties involved; neither IANA nor the IETF 924 will become involved in such disputes except in response to orders 925 from a court of competent jurisdiction. 927 5.2. Informal Namespaces 929 Informal namespaces are full-fledged URN namespaces, with all the 930 associated rights and responsibilities. Informal namespaces differ 931 from formal namespaces in the process for assigning a NID: for an 932 informal namespace, the registrant does not designate the NID; 933 instead, IANA assigns a NID consisting of the string 'urn-' followed 934 by one or more digits (e.g., "urn-7") where the digits consist of the 935 next available number in the sequence of positive integers assigned 936 to informal namespaces. Thus the syntax of an informal namespace is: 938 InformalNamespaceName = "urn-" Number 939 Number = DigitNonZero 0*Digit 940 DigitNonZero = "1"/ "2" / "3" / "4"/ "5" 941 / "6" / "7" / "8" / "9" 942 Digit = "0" / DigitNonZero 944 The only restrictions on are that it (1) consist strictly of 945 ASCII digits, that it (2) not have leading zeros, and that it (3) not 946 cause the NID to exceed the length limitations defined for the URN 947 syntax. 949 6. Defining and Registering a URN Namespace 951 6.1. Overview 953 Because the space of URN namespaces is itself managed, the definition 954 of a namespace SHOULD pay particular attention to: 956 1. The purpose of the namespace. 958 2. The syntax of URNs assigned within the namespace, including the 959 internal syntax and anticipated effects of q-components or 960 r-components. (The syntax and interpretation of f-components are 961 defined in RFC 3986.) 963 3. The process for assigning URNs within the namespace. 965 4. The security implications of assigning URNs within the namespace 966 and using the assigned URNs. 968 5. Any potential interoperability issues with URNs assigned within 969 the namespace. 971 6. Optionally, the process for resolving URNs issued within the 972 namespace. 974 The section on completing the template (Section 6.4) explains these 975 matters in greater detail. Although the registration templates are 976 the same in all cases, slightly different procedures are used 977 depending on the source of the registration. 979 6.2. Registration Policy and Process: Community Registrations 981 The basic registration policy for URN namespaces is Expert Review as 982 defined in the "IANA Considerations" document [RFC5226]. For 983 namespaces or their definitions that are intended to become standards 984 or normative components of standards, the output of the Expert Review 985 process is intended to be a report, rather than instructions to IANA 986 to take action (see below). The key steps are: 988 1. Fill out the namespace registration template (see Section 6.4 and 989 Appendix A). This can be done as part of an Internet-Draft or a 990 specification in another series, although that is not necessary. 992 2. Send the completed template to the urn@ietf.org discussion list 993 for review. 995 3. If necessary to address comments received, repeat steps 1 and 2. 997 4. If the designated experts approve the request and no 998 standardization action is involved, the IANA will register the 999 requested NID. If standardization is anticipated, the designated 1000 experts will prepare a report and forward it to the appropriate 1001 standards approval body (the IESG in the case of the IETF); IANA 1002 will register the requested NID only after receiving directions 1003 from that body and a copy of the expert review report. 1005 A namespace registration can be revised by updating the registration 1006 template, following the same steps outlined above for new 1007 registrations. A revised registration MUST describe differences from 1008 prior versions and SHOULD make special note of any relevant changes 1009 in the underlying technologies or namespace management processes. 1011 Experience to date with namespace registration requests has shown 1012 that registrants sometimes do not initially understand some of the 1013 subtleties of URN namespaces, and that defining the namespace in the 1014 form of a specification enables the registrants to clearly formulate 1015 their "contract" with the intended user community. Therefore, 1016 although the registration policy for formal namespaces is Expert 1017 Review and a specification is not strictly required, registrants 1018 SHOULD provide a stable specification documenting the namespace 1019 definition and expanding upon the issues described herein. 1021 Because naming can be difficult and contentious, namespace 1022 registrants and the designated experts are strongly encouraged to 1023 work together in a spirit of good faith and mutual understanding to 1024 achieve rough consensus (see [RFC7282]) on handling registration 1025 requests. They are also encouraged to bring additional expertise 1026 into the discussion if that would be helpful in providing perspective 1027 or otherwise resolving issues. 1029 Especially when iterations in the registration process are prolonged, 1030 designated experts are expected to take reasonable precautions to 1031 avoid "race conditions" on proposed NID names and, if such situations 1032 arise, to encourage applicants to work out any conflicts among 1033 themselves. 1035 6.3. Registration Policy and Process: Fast Track for Standards 1036 Development Organizations, Scientific Societies, and Similar 1037 Bodies 1039 The IETF recognizes that situations will arise in which URN 1040 namespaces will be created to either embed existing and established 1041 standards, particularly identifier standards, or to reflect 1042 knowledge, terminology, or methods of organizing information that lie 1043 well outside the IETF's scope or the likely subject matter knowledge 1044 of its Designated Experts. In situations in which the registration 1045 request originates from, or is authorized by, a recognized standards- 1046 related organization, scientific society, or similar body, a somewhat 1047 different procedure is available at the option of that body: 1049 1. The namespace registration template is filled out and submitted 1050 as in steps 1 and 2 above. 1052 2. A specification is required that reflects or points to the needed 1053 external standards or specifications. Publication in the RFC 1054 Series or through an IETF process (e.g., posting as an Internet 1055 Draft) is not expected and would be appropriate only under very 1056 unusual circumstances. 1058 3. The reviews on the discussion list and by the designated experts 1059 are strictly advisory, with the decisions about what advice to 1060 accept and the length of time to allocate to the process strictly 1061 under the control of the external body. 1063 4. When that body concludes that the application is sufficiently 1064 mature, its represenative(s) will request that IANA complete the 1065 registration for the NID, and IANA will do so. 1067 Decisions about whether to recognize the requesting entity as a 1068 standards-related organization, scientific society, or similar body 1069 are the responsibility of the IESG. 1071 A model similar to this has already been defined for recognized 1072 standards-related organizations that wish to register Media Types. 1073 The document describing that mechanism [RFC6838] provides somewhat 1074 more information about the general approach. 1076 6.4. Completing the Template 1078 A template for defining and registering a URN namespace is provided 1079 in Appendix A. This section describes considerations for completing 1080 the template. 1082 6.4.1. Purpose 1084 The "Purpose" section of the template describes matters such as: 1086 1. The kinds of resources identified by URNs assigned within the 1087 namespace. 1089 2. The scope and applicability of the URNs assigned within the 1090 namespace; this might include information about the community of 1091 use (e.g., a particular nation, industry, technology, or 1092 organization), whether the assigned URNs will be used on public 1093 networks or private networks, etc. 1095 3. How the intended community (and the Internet community at large) 1096 will benefit from using or resolving the assigned URNs. 1098 4. How the namespace relates to and complements existing URN 1099 namespaces, URI schemes, and identifier systems. 1101 5. The kinds of software applications that can use or resolve the 1102 assigned URNs (e.g., by differentiating among disparate 1103 namespaces, identifying resources in a persistent fashion, or 1104 meaningfully resolving and accessing services associated with the 1105 namespace). 1107 6. Whether resolution services are available or will be available 1108 (and, if so, the nature or identity of the services). Examples 1109 of q-component and, when they are standardized, r-component, 1110 semantics and syntax are helpful here, even if detailed 1111 definitions are provided elsewhere later. 1113 7. Whether the namespace or its definition is expected to become an 1114 integral or normative element of a standard being developed in 1115 the IETF or some other recognized standards body. 1117 6.4.2. Syntax 1119 The "Syntax" section of the template contains: 1121 1. A description of the structure of URNs within the namespace, in 1122 conformance with the fundamental URN syntax. The structure might 1123 be described in terms of a formal definition (e.g., using 1124 Augmented BNF for Syntax Specifications (ABNF) as specified in 1125 [RFC5234]), an algorithm for generating conformant URNs, or a 1126 regular expression for parsing the identifier into components; 1127 alternatively, the structure might be opaque. 1129 2. Any special character encoding rules for assigned URNs (e.g., 1130 which character ought to always be used for quotes). 1132 3. Rules for determining equivalence between two identifiers in the 1133 namespace. Such rules ought to always have the effect of 1134 eliminating false negatives that might otherwise result from 1135 comparison. If it is appropriate and helpful, reference can be 1136 made to specific equivalence rules defined in the URI 1137 specification [RFC3986]. Examples of equivalence rules include 1138 equivalence between uppercase and lowercase characters in the 1139 Namespace Specific String, between hyphenated and non-hyphenated 1140 groupings in the identifier string, or between single-quotes and 1141 double-quotes. There may also be namespace-specific special 1142 encoding considerations, especially for URNs that contain 1143 embedded forms of other types of identifiers. (Note that these 1144 are not normative statements for any kind of best practice 1145 related to handling of equivalences between characters in 1146 general; such statements are limited to one particular namespace 1147 only.) 1149 4. Any special considerations necessary for conforming with the URN 1150 syntax. This is particularly applicable in the case of existing 1151 naming systems that are used in the context of URNs. For 1152 example, if a namespace is used in contexts other than URNs, it 1153 might make use of characters that are reserved in the URN syntax. 1154 This section ought to note any such characters, and outline 1155 necessary mappings to conform to URN syntax. Normally, this will 1156 be handled by percent-encoding the character as specified in 1157 Section 2.1 of the URI specification [RFC3986]. 1159 5. Any special considerations for the meaning of q-components (e.g., 1160 keywords) or f-components (e.g., predefined terms) in the context 1161 of this namespace. 1163 6.4.3. Assignment 1165 The "Assignment" section of the template describes matters such as: 1167 1. Mechanisms or authorities for assigning URNs to resources. It 1168 ought to make clear whether assignment is completely open (e.g., 1169 following a particular procedure such as first-come, first-served 1170 (FCFS)), completely closed (e.g., for a private organization), or 1171 limited in various ways (e.g., delegated to authorities 1172 recognized by a particular organization); if limited, it ought to 1173 explain how to become an assigner of identifiers or how to 1174 request assignment of identifiers from existing assignment 1175 authorities. 1177 2. Methods for ensuring that URNs within the namespace are unique. 1178 For example, identifiers might be assigned sequentially or in 1179 accordance with some well-defined process by a single authority, 1180 assignment might be partitioned among delegated authorities that 1181 are individually responsible for respecting uniqueness rules, or 1182 URNs might be created independently following an algorithm that 1183 itself guarantees uniqueness. 1185 6.4.4. Security and Privacy 1187 The "Security and Privacy" section of the template describes any 1188 potential issues related to security and privacy with regard to 1189 assignment, use, and resolution of identifiers within the namespace. 1190 Examples of such issues include: 1192 o The consequences of producing false negatives and false positives 1193 during comparison for equivalence (see "Issues in Identifier 1194 Comparison for Security Purposes" [RFC6943]) 1196 o Leakage of private information when identifiers are communicated 1197 on the public Internet 1199 o The potential for directory harvesting 1201 o Various issues discussed in the guidelines for security 1202 considerations in RFCs [RFC3552] and the privacy considerations 1203 for Internet protocols [RFC6973]. 1205 6.4.5. Interoperability 1207 The "Interoperability" section MUST specify any known potential 1208 issues related to interoperability. Examples include possible 1209 confusion with other URN namespaces or naming systems because of 1210 syntax (e.g., percent-encoding of certain characters) or scope (e.g., 1211 overlapping areas of interest). If at all possible, concerns that 1212 arise during the registration of a URN namespace (e.g., due to the 1213 syntax or scope of an identifier system) should be resolved as part 1214 of or in parallel to the registration process. 1216 6.4.6. Resolution 1218 The "Resolution" section MUST specify whether resolution mechanisms 1219 are intended or anticipated for URNs assigned within the namespace 1220 (e.g., URNs within some namespaces are intended to act as abstract 1221 designators and thus are not intended to be resolved). 1223 If resolution is intended, then this section SHOULD specify whether 1224 the organization that assigns URNs within the namespace intends to 1225 operate or recommend any resolution services for URNs within that 1226 namespace. In addition, if the assigning organization intends to 1227 implement registration for publicly advertised resolution services 1228 (for example using a system based on principles similar to those 1229 described in [RFC2276] and [RFC2483]), then this section SHOULD list 1230 or reference the requirements for being publicly advertised by the 1231 assigning organization. In addition, this section SHOULD describe 1232 any special considerations for the handilng of r-components in the 1233 context of this namespace. 1235 6.4.7. Additional Information 1237 Please include any additional information that would be useful to 1238 those trying to understand this registration or its relationship to 1239 others, such as comparisons to existing namespaces that might seem to 1240 overlap. 1242 This section of the template is optional. 1244 7. IANA Considerations 1246 7.1. URI Scheme 1248 This section updates the registration of the 'urn' URI scheme in the 1249 Permanent URI Registry [URI-Registry] . 1251 [Note to RFC Editor: please replace "[ this document ]" with "RFC" 1252 and the number assigned to this document upon publication.] 1254 URI Scheme Name: urn 1256 Status: permanent 1258 URI Scheme Syntax: See Section 2 of [ this document ]. 1260 URI Scheme Semantics: The 'urn' scheme identifies Uniform Resource 1261 Names, which are persistent, location-independent resource 1262 identifiers. 1264 Encoding Considerations: See Section 2 of [ this document ]. 1266 Applications/Protocols That Use This URI Scheme Name: Uniform 1267 Resource Names are used in a wide variety of applications, 1268 including bibliographic reference systems and as names for 1269 Extensible Markup Language (XML) namespaces. 1271 Interoperability Considerations: See Section 4 of [ this document ]. 1273 Security Considerations: See Section 6.4.4 and Section 8 of [ this 1274 document ]. 1276 Contact: URNBIS WG [mailto:urn@ietf.org] 1278 Author/Change Controller: This scheme is registered under the IETF 1279 tree. As such, the IETF maintains change control. 1281 References None. 1283 7.2. Registration of URN Namespaces 1285 This document outlines the processes for registering URN namespaces, 1286 and has implications for the IANA in terms of registries to be 1287 maintained (see especially Section 6). In all cases, the IANA ought 1288 to assign the appropriate NID (formal or informal) once the 1289 procedures outlined in this document have been completed. 1291 8. Security and Privacy Considerations 1293 The definition of a URN namespace needs to account for potential 1294 security and privacy issues related to assignment, use, and 1295 resolution of identifiers within the namespace (e.g., some namespace 1296 resolvers might assign special meaning to certain characters in the 1297 Namespace Specific String); see Section 6.4.4 for further discussion. 1299 In most cases, URN namespaces provide a way to declare public 1300 information. Normally, these declarations will have a relatively low 1301 security profile, however there is always the danger of "spoofing" 1302 and providing misinformation. Information in these declarations 1303 ought to be taken as advisory. 1305 9. References 1307 9.1. Normative References 1309 [RFC20] Cerf, V., "ASCII format for network interchange", RFC 20, 1310 October 1969. 1312 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1313 Requirement Levels", BCP 14, RFC 2119, March 1997. 1315 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 1316 Resource Identifier (URI): Generic Syntax", STD 66, 1317 RFC 3986, January 2005. 1319 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1320 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1321 May 2008. 1323 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 1324 Specifications: ABNF", STD 68, RFC 5234, January 2008. 1326 9.2. Informative References 1328 [DOI-URI] Paskin, N., Neylon, E., Hammond, T., and S. Sun, "The 1329 "doi" URI Scheme for the Digital Object Identifier (DOI)", 1330 June 2003, 1331 . 1333 [I-D.ietf-urnbis-semantics-clarif] 1334 Klensin, J., "URN Semantics Clarification", draft-ietf- 1335 urnbis-semantics-clarif-03 (work in progress), February 1336 2016. 1338 [ISO3166-1] 1339 ISO, "Codes for the representation of names of countries 1340 and their subdivisions -- Part 1: Country codes", 1341 ISO 3166-1:2013, 2013. 1343 [RFC1737] Sollins, K. and L. Masinter, "Functional Requirements for 1344 Uniform Resource Names", RFC 1737, December 1994. 1346 [RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997. 1348 [RFC2276] Sollins, K., "Architectural Principles of Uniform Resource 1349 Name Resolution", RFC 2276, January 1998. 1351 [RFC2483] Mealling, M. and R. Daniel, "URI Resolution Services 1352 Necessary for URN Resolution", RFC 2483, January 1999. 1354 [RFC3044] Rozenfeld, S., "Using The ISSN (International Serial 1355 Standard Number) as URN (Uniform Resource Names) within an 1356 ISSN-URN Namespace", RFC 3044, January 2001. 1358 [RFC3187] Hakala, J. and H. Walravens, "Using International Standard 1359 Book Numbers as Uniform Resource Names", RFC 3187, October 1360 2001. 1362 [RFC3406] Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom, 1363 "Uniform Resource Names (URN) Namespace Definition 1364 Mechanisms", BCP 66, RFC 3406, October 2002. 1366 [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC 1367 Text on Security Considerations", BCP 72, RFC 3552, July 1368 2003. 1370 [RFC4854] Saint-Andre, P., "A Uniform Resource Name (URN) Namespace 1371 for Extensions to the Extensible Messaging and Presence 1372 Protocol (XMPP)", RFC 4854, April 2007. 1374 [RFC5122] Saint-Andre, P., "Internationalized Resource Identifiers 1375 (IRIs) and Uniform Resource Identifiers (URIs) for the 1376 Extensible Messaging and Presence Protocol (XMPP)", 1377 RFC 5122, February 2008. 1379 [RFC5890] Klensin, J., "Internationalized Domain Names for 1380 Applications (IDNA): Definitions and Document Framework", 1381 RFC 5890, August 2010. 1383 [RFC6648] Saint-Andre, P., Crocker, D., and M. Nottingham, 1384 "Deprecating the "X-" Prefix and Similar Constructs in 1385 Application Protocols", BCP 178, RFC 6648, June 2012. 1387 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type 1388 Specifications and Registration Procedures", BCP 13, 1389 RFC 6838, January 2013. 1391 [RFC6943] Thaler, D., "Issues in Identifier Comparison for Security 1392 Purposes", RFC 6943, May 2013. 1394 [RFC6963] Saint-Andre, P., "A Uniform Resource Name (URN) Namespace 1395 for Examples", BCP 183, RFC 6963, May 2013. 1397 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 1398 Morris, J., Hansen, M., and R. Smith, "Privacy 1399 Considerations for Internet Protocols", RFC 6973, July 1400 2013. 1402 [RFC7282] Resnick, P., "On Consensus and Humming in the IETF", 1403 RFC 7282, June 2014. 1405 [RFC7320] Nottingham, M., "URI Design and Ownership", BCP 190, 1406 RFC 7320, July 2014. 1408 [RFC7613] Saint-Andre, P. and A. Melnikov, "Preparation, 1409 Enforcement, and Comparison of Internationalized Strings 1410 Representing Usernames and Passwords", RFC 7613, 1411 DOI 10.17487/RFC7613, August 2015, 1412 . 1414 [UAX31] The Unicode Consortium, "Unicode Standard Annex #31: 1415 Unicode Identifier and Pattern Syntax", June 2015, 1416 . 1418 [UNICODE] The Unicode Consortium, "The Unicode Standard", 2015, 1419 . 1421 [URI-Registry] 1422 IANA, "Permanent URI Schemes", 1423 . 1426 [XML-BASE] 1427 Marsh, J. and R. Tobin, "XML Base (Second Edition)", World 1428 Wide Web Consortium Recommendation REC-xmlbase-20090128, 1429 January 2009, 1430 . 1432 [XML-NAMES] 1433 Thompson, H., Hollander, D., Layman, A., Bray, T., and R. 1434 Tobin, "Namespaces in XML 1.0 (Third Edition)", World Wide 1435 Web Consortium Recommendation REC-xml-names-20091208, 1436 December 2009, 1437 . 1439 Appendix A. Registration Template 1441 Namespace ID: Requested of IANA (formal) or assigned by IANA 1442 (informal). 1444 Version: The version of the registration, starting with 1 and 1445 incrementing by 1 with each new version. 1447 Date: The date when the registration is requested of IANA, using the 1448 format YYYY-MM-DD. 1450 Registrant: The person or organization that has registered the NID, 1451 including the name and address of the registering organization, as 1452 well as the name and contact information (email, phone number, or 1453 postal address) of the designated contact person. If the 1454 registrant is a recognized standards development organization or 1455 scientific society requesting the fact track registration 1456 procedure (see Section 6.3), that information should be clearly 1457 indicated in this section of the template. 1459 Purpose: Described under Section 6.4.1 of this document. 1461 Syntax: Described under Section 6.4.2 of this document. Unless the 1462 registration explicitly says otherwise, use of q-components and 1463 f-components is not allowed for this namespace. 1465 Assignment: Described under Section 6.4.3 of this document. 1467 Security and Privacy: Described under Section 6.4.4 of this 1468 document. 1470 Interoperability: Described under Section 6.4.5 of this document. 1472 Resolution: Described under Section 6.4.6 of this document. 1474 Documentation: A pointer to an RFC, a specification published by 1475 another standards development organization, or another stable 1476 document that provides further information about the namespace. 1478 Additional Information Described under Section 6.4.7 of this 1479 document. 1481 Revision Information: Description of changes from prior version(s). 1482 (Applicable only when earlier registrations have been revised.) 1484 Additional Information: Any additional information that would be 1485 useful to the reader or those trying to understand the 1486 registration, perhaps in context with other work. May be a 1487 reference to another document or omitted if not needed. 1489 Appendix B. Changes from RFC 2141 1491 This document makes substantive changes from the syntax and semantics 1492 of [RFC2141]: 1494 B.1. Syntax changes from RFC 2141 1496 The syntax of URNs as provided in [RFC2141] was defined before the 1497 updated specification of URIs in [RFC3986]. The definition of URN 1498 syntax is updated in this document to do the following: 1500 o Ensure consistency with the URI syntax. 1502 o Facilitate the use of URNs with parameters similar to URI queries 1503 and fragments. 1505 o Permit parameters influencing URN resolution. 1507 o Ease the use of URNs with naming systems that include the '/' 1508 character. 1510 In particular, this specification does the following: 1512 o Extends URN syntax to explicitly allow the characters '/', "?", 1513 and "#", which were reserved for future use by RFC 2141. As 1514 described below, this change effectively also allows several 1515 components of the URI syntax although without necessarily tying 1516 those components to URI semantics. 1518 o Defines general syntax for an additional component that can be 1519 used in interactions with a URN resolution service. 1521 o Disallows "-" at the end of a NID. 1523 o Allows the "/", "~", and "&" characters in the namespace-specific 1524 string (NSS). 1526 o Makes several smaller syntax adjustments. 1528 B.2. Other changes from RFC 2141 1530 o Formally registers 'urn' as a URI scheme. 1532 o Allows what are now called q-components, r-components, and 1533 f-components. 1535 In addition, some of the text has been updated to be consistent with 1536 the definition of Uniform Resource Identifiers (URIs) [RFC3986] and 1537 the processes for registering information with the IANA [RFC5226], as 1538 well as more modern guidance with regard to security [RFC3552] and 1539 privacy [RFC6973] issues and identifier comparison [RFC6943]. 1541 Appendix C. Changes from RFC 3406 1543 This document makes the following substantive changes from [RFC3406]: 1545 1. Relaxes the registration policy for formal namespaces from "IETF 1546 Review" to "Expert Review" as discussed in Section 6.2. 1548 2. Removes the category of experimental namespaces, consistent with 1549 [RFC6648]. Experimental namespaces were denoted by prefixing the 1550 namespace identifier with the string "X-". Because experimental 1551 namespaces were never registered, removing the experimental 1552 category has no impact on the existing registries. Because they 1553 are not registered, strings that refer to experimental namespaces 1554 are not valid URNs. Truly experimental usages MAY, of course, 1555 employ the 'example' namespace [RFC6963]. 1557 3. Adds some information too, but generally simplifies, the 1558 registration template. 1560 Appendix D. Contributors 1562 RFC 2141, which provided the basis for the syntax portion of this 1563 document, was authored by Ryan Moats. 1565 RFC 3406, which provided the basis for the namespace portion of this 1566 document, was authored by Leslie Daigle, Dirk-Willem van Gulik, 1567 Renato Iannella, and Patrik Faltstrom. 1569 Their work is gratefully acknowledged. 1571 Appendix E. Acknowledgements 1573 Many thanks to Marc Blanchet, Leslie Daigle, Martin Duerst, Juha 1574 Hakala, Ted Hardie, Alfred Hoenes, Paul Jones, Barry Leiba, Sean 1575 Leonard, Larry Masinter, Keith Moore, Mark Nottingham, Julian 1576 Reschke, Lars Svensson, Henry S. Thompson, Dale Worley, and other 1577 participants in the URNBIS WG for their input. Alfred Hoenes in 1578 particular edited an earlier version of this document and served as 1579 co-chair of the URNBIS WG. 1581 Juha Hakala deserves special recognition for his dedication to 1582 successfully completing this work, as do Andrew Newton and Melinda 1583 Shore in their roles as working group co-chairs and Barry Leiba in 1584 his role as area director and then as co-chair. 1586 Appendix F. Change log for versions of draft-ietf-urnbis-rfc2141bis-urn 1588 [[RFC Editor: please remove this appendix before publication.]] 1590 F.1. Changes from -08 to -09 1592 o Altered the text in Section 4 to reflect list discussions about 1593 the earlier phrasing. Also added DOI example and citation to that 1594 section. 1596 o Clarified the naming rules for formal namespaces and their 1597 relationship to ISO 3166, IDNA, etc., reserved strings. 1599 o Added an explicit statement about use of URNs in various protocols 1600 and contexts to Section 4. 1602 o Clarified that experimental namespace NIDs, which were explicitly 1603 not registered, are not valid URNs (in Section 5. 1605 o Transformed the partial production in Section 5.2 into valid ABNF. 1607 o Added more text about p-/q-/f-components and recommendations about 1608 use. 1610 o Added clarifying note about "?" within q-components and 1611 f-components. 1613 o Added explicit requirement that revisions of existing 1614 registrations document the changes and added a slot for that 1615 description to the template. 1617 o Many small editorial changes and adjustments including adding 1618 additional references and cross-references for clarification. 1620 o Inserted a placeholder for additional examples. 1622 F.2. Changes from -09 to -10 1624 o Several clarifying editorial changes, most suggested by Ted Hardie 1625 and Henry S. Thompson (some of them off-list). 1627 o Added a large number of placeholders that identify issues that 1628 require WG consideration and resolution (or WG delegation to the 1629 editors). 1631 F.3. Changes from -10 to -11 1633 o Removed most of the placeholders added in -10. Supplied new text 1634 as required or suggested by on-list discussion of those issues. 1636 o Replaced the conformance examples Section 3.2 with a more complete 1637 collection and discussion. 1639 o Revised and consolidated the registration procedure, and added 1640 provisions for NIDs that are the subject of standards and for 1641 avoiding race conditions about NID strings. 1643 o In response to independent comments from Ted Hardie and Henry S. 1644 Thompson, called attention to the possibility of conflicts between 1645 NID strings and various claims of national, corporate, and other 1646 perogatives. 1648 o Changed the production for assigned-name as suggested by Lars 1649 Svensson. 1651 o Several clarifying editorial changes including correcting a glitch 1652 in instructions to the RFC Editor. 1654 F.4. Changes from -11 to -12 1656 o Removed p-components as a standalone construct, and instead folded 1657 them into the NSS. 1659 o Defined syntax for r-components as a way to pass information to 1660 resolvers, but left the semantics for future standardization 1661 efforts. 1663 o Further tuned the discussion of interoperability and related 1664 registration issues. 1666 o Made a number of editorial corrections and reorganized the syntax 1667 material in Section 2 somewhat to make it internally consistent 1668 and keep the relationship to RFC 3986 clear. 1670 F.5. Changes from -12 to -13 1672 o More precisely defined the semantics of the optional components. 1674 o Defined the term "resolution" and clarified several related 1675 matters throughout the text. 1677 o Clarified terminological relationship to RFC 3986. 1679 o Further cleansed the document of p-components. 1681 o Corrected several examples to avoid confusion with existing 1682 identifier systems. 1684 o Improved text regarding the purpose of namespaces being 1685 registered. 1687 F.6. Changes from -13 to -14 1689 o Reverted the ABNF to what had been defined in version -12. 1691 o Added fast-track approval process for standards-related 1692 organizations, scientific societies, and similar bodies (similar 1693 to RFC 6838 for Media Types). 1695 F.7. Changes from -14 to -15 1697 o Reorganized the Introduction slightly, adding new subsection 1.1 1698 and making Terminology (the former Section 2) Section 1.2. 1700 o Tightened the discussion of "resolution" somewhat to try to 1701 mitigate some on-list confusion. 1703 o Added some text about character set choices and repertoires 1704 (consistent with the Section 1.1 explanation). 1706 o Moved away from "?" and "??" for q-component and r-component 1707 delimiters and went to two-character sequences for each. This 1708 includes several changes to the text to remove or modify 1709 discussions of string termination and the role of a question mark 1710 not followed by one of the new delimiters. 1712 o Redefined r-component to be an ASCII resolver ID and a string. 1713 Neither is further defined in this specification and text has been 1714 added to say that. 1716 o Several editorial changes to improve clarity, most following up on 1717 comments made on the list. These included modifying the table of 1718 contents so that the subsections on optional components now appear 1719 there. 1721 F.8. Changes from -15 (2016-02-04) to -16 1723 o Rewrote the introductory material to make the relationship to 1724 other specifications more clear and allow removing or altering 1725 text that was stated in terms of changes from 2141. The 1726 specification is now self-contained with regard to the earlier 1727 definitions and descriptions of URNs. 1729 o Removed the parts of Section 2 that were really a description of 1730 changes from RFC 2141 to Appendix B, where such changes are 1731 enumerated. Similarly, removed most material describing changes 1732 from RFC 3406 to Appendix C. 1734 o Replaced one example. 1736 o Rearranged and rewrote text to improve clarity and relationships 1737 to other documents and to reduce redundant material. 1739 o Made it more clear that r-components, despite the partial syntax 1740 specification, are reserved for future standardization. 1742 o Clarified that there can be URNs that neither resolve to URLs nor 1743 are abstract designators. 1745 o Added pointers to make it clear that the Syntax material in 1746 Section 2 is not self-contained, e.g., that its subsections and 1747 other sections further restrict strings that can be used for NIDs 1748 and so on. 1750 o Added an "Additional Information" section to the registration 1751 template. See list discussion on and about 2016-03-18. 1753 o Minor editorial/ typographic fixes (per comment from Lars). 1755 Authors' Addresses 1757 Peter Saint-Andre 1758 Filament 1760 Email: peter@filament.com 1761 URI: https://filament.com/ 1762 John C Klensin 1763 1770 Massachusetts Ave, Ste 322 1764 Cambridge, MA 02140 1765 USA 1767 Phone: +1 617 245 1457 1768 Email: john-ietf@jck.com