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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 URN Working Group M.Mealling 2 INTERNET-DRAFT Network Solutions, Inc. 3 Expires six months from March 1998 Ron Daniel Jr. 4 Intended category: Experimental Los Alamos National Laboratory 5 draft-ietf-urn-resolution-services-05.txt 7 URI Resolution Services 8 Necessary for URN Resolution 10 Status of this Memo 12 This document is an Internet-Draft. Internet-Drafts are working 13 documents of the Internet Engineering Task Force (IETF), its areas, 14 and its working groups. Note that other groups may also distribute 15 working documents as Internet-Drafts. 17 Internet-Drafts are draft documents valid for a maximum of six months 18 and may be updated, replaced, or obsoleted by other documents at 19 any time. It is inappropriate to use Internet-Drafts as reference 20 material or to cite them other than as work in progress. 22 To learn the current status of any Internet-Draft, please check the 23 1id-abstracts.txt listing contained in the Internet-Drafts Shadow 24 Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe), 25 ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). 27 Abstract 29 Retrieving the resource identified by a Uniform Resource Identifier 30 (URI) [3] is only one of the operations that can be performed on a URI. 31 One might also ask for and get a list of other identifiers that are 32 aliases for the original URI or a bibliographic description of the 33 resource the URI denotes, for example. This applies to both Uniform 34 Resource Names (URNs) and Uniform Resource Locators (URLs). Uniform 35 Resource Characteristics (URCs) are discussed in this document but only 36 as descriptions of resources rather than identifiers. 38 A service in the network providing access to a resource may provide 39 one or some of these options, but it need not provide all of them. This 40 memo specifies an initial set of these functions, to be used to 41 describe the functions provided by any given access service and the 42 requirements that must be met when those operations are encoded in a 43 protocol. 45 1. Introduction 47 In the course of formulating current proposals [1] regarding URNs 48 [2], it became apparent that requiring servers to deal with all desired 49 functions or requiring clients to deal with complicated information 50 returned by a server was unrealistic and a barrier to adoption. There 51 needed to be some way for a client to be able to pick between a server 52 that specialized in the complex and another that specialized in the 53 simple (but fast). Also, in subsequent conversations it became obvious 54 that, in most cases, some of the operations were inappropriate or 55 difficult for certain identifiers. 57 The Problem 59 In the process of learning about a resource in the Internet, there 60 are a variety of possible functions that may be important or useful, 61 such as discovery of locators, names, descriptions, and accessing the 62 resource itself. A given service may support only a subset of these; 63 hence, it is important to describe such an access service by the types 64 of functions it supports, those resources about which it knows 65 anything. For example, in the framework for an RDS described in [5] the 66 RDS itself may provide URLs [6][7], while the resolvers may provide 67 descriptions, URLs, or even the resources themselves. The design of an 68 RDS, as proposed in RFC 2168 [1], may be more generous and provide all 69 of the above. 71 This problem requires some well understood set of identifiers that 72 identify those operations. But an exhaustive set would both be 73 impossible and not very necessary. Thus, this document will list 74 several operations as well as lay out requirements for specifying new 75 operations. 77 The purpose of this document is to define a list of such functions 78 and short names for them and use them in defining the interface to an 79 access service. Previous versions of this document referred to services 80 where the arguments were specific types of URIs such as URNs or URLs. 81 These services were called "N2L" and "L2L",for example. Their use has 82 been changed in favor of the more general URI form. 84 Design Criteria 86 The design criteria used to meet these requirements were fairly 87 simple. The need to identify the operation with some token and know its 88 operands, algorithm, and errors was sufficient to meet the 89 requirements. 91 2. General Specification 93 To provide a framework both for the specifications in this document 94 and for future work to be written by others, the guidelines below are 95 suggested for documents that seek to specify new operations. Any 96 specification of a member of this set of operations should address 97 these issues with respect to its operands, its algorithm, output, and errors. 99 Due to the small number of listed functions, a registration mechanism 100 was dismissed as premature. If this list grows, a registration mechanism 101 will probably be needed. 103 Also, due to the experimental nature of this document and the systems 104 that use its specifications, the use of words like MUST and SHALL are 105 limited. Where used they reflect a case where this specification could 106 cause harm to existing, non-experimental systems such as HTTP and URNs. 107 Thus, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 108 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 109 document are to be interpreted as described in RFC 2119. 111 2.1 Operands 113 Operands must contain the following pieces of information: 115 * name of the operation 116 * case insensitive mnemonic for the operation 117 * number of operands 118 * type of each operand 119 * format of each operand 121 2.2 Algorithm 123 The exact algorithm for the operation must be specified, or it must 124 be specified that the algorithm is opaque and defined by the server. 126 2.3 Output 128 Output must specify one of the following: 130 * there is no output 131 * the output is undefined 132 * the output itself and its content 133 * the fact that the output is an object and the object's 134 type and format 135 * any non-protocol specific errors 137 2.4 Error Conditions 139 All errors that are considered applicable across all implementations 140 and application environments must be included. Errors that depend on 141 the system conveying the service are not included. Thus, many of the 142 expected errors such as service availability or operation syntax are 143 not included in this document since they are implementation dependent. 145 2.5 Security Considerations 147 Any security considerations relating to the service provided must be 148 specified. This does NOT include considerations dealing with the 149 protocol used to convey the service or to those that normally accompany 150 the results of the service. For example, an I2L service would need to 151 discuss the situation where someone maliciously inserts an incorrect 152 URL into the resolver but NOT the case where someone sends personal 153 information across the Internet to the resource identified by the 154 correct URL. 156 3. Encoding The Operations 158 To be useful, these operations have to be used within some system or 159 protocol. In many cases, these systems and protocols will place 160 restrictions on which operations make sense and how those that do are 161 syntactically represented. It is sufficient for those protocols to 162 define new operations within their own protocol specification 163 documents but care should be taken to make this fact well known. 165 Also, a given system or protocol will have its own output specifications 166 that may restrict the output formats of a given operation. 167 Additionally, a given protocol may have better solution for output 168 than the ones given here. For example, the I2L result may be 169 encoded in a protocol-specific manner that conveys information about 170 the closeness of each resource on the network. 172 Thus, the requirements on encoding these operations within a given 173 system are as follows: 175 * which subset of the operations are allowed 176 * how the operator is encoded 177 * how the operands are encoded 178 * how the error codes are returned 180 The text/uri-list MIME Media Type is specified in Section 5. This Media Type 181 is merely a suggestion for experimental systems that need a simple 182 implementation. It is included here merely as an example to show 183 completeness (however simple it may be). 185 4. The Incomplete Set 187 4.1 I2L (URI to URL) 189 * Name: URI to URL 190 * Mnemonic: I2L 191 * Number of Operands: 1 192 * Type of Each Operand: First operand is a URI. 193 * Format of Each Operand: First operand is encoded as a URI. 194 * Algorithm: Opaque 195 * Output: One and only one URL 196 * Errors Conditions: 197 o Malformed URI 198 o URI is syntactically valid but does not exist in any form. 199 o URI exists but there is no available output from this 200 operation. 201 o URI existed in the past but nothing is currently known 202 about it. 203 o Access denied 205 * Security Considerations: 206 o Malicious Redirection 207 One of the fundamental dangers related to any service such as 208 this is that a malicious entry in a resolver's database will 209 cause clients to resolve the URI into the wrong URL. The 210 possible intent may be to cause the client to retrieve a 211 resource containing fraudulent or damaging material. 212 o Denial of Service 213 By removing the URL to which the URI maps, a malicious 214 intruder may remove the client's ability to retrieve the 215 resource. 217 This operation is used to map a single URI to a single URL. It is 218 used by lightweight clients that do not have the ability to select from 219 a list of URLs or understand a URC. The algorithm for this mapping is 220 dependent on the URI scheme. 222 4.2 I2Ls (URI to URLs) 224 * Name: URI to URLs 225 * Mnemonic: I2LS 226 * Number of Operands: 1 227 * Type of Each Operand: First operand is a URI. 228 * Format of Each Operand: First operand is encoded as a URI. 229 * Algorithm: Opaque 230 * Output: A list of zero or more URLs 231 * Errors: 232 o Malformed URI 233 o URI is syntactically valid but does not exist in any form. 234 o URI exists but there is no available output from this 235 operation. 236 o URI existed in the past but nothing is currently known 237 about it. 238 o Access denied 239 * Security Considerations: 240 o Malicious Redirection (see I2L) 241 o Denial of Service (see I2L) 243 This operation is used to map a single URI to 0 or more URLs. It is 244 used by a client that can pick from a list of URLs based on some 245 criteria that are important to the client. The client should not make 246 any assumptions about the order of the URLs returned. No matter what 247 the particular media type, the result should be a list of the URLs that 248 may be used to obtain an instance of the resource identified by the 249 URI. All URIs shall be encoded according to the URI specification [3]. 251 4.3 I2R (URI to Resource) 253 * Name: URI to Resource 254 * Mnemonic: I2R 255 * Number of Operands: 1 256 * Type of Each Operand: First operand is a URI. 257 * Format of Each Operand: First operand is encoded as a URI. 258 * Algorithm: Opaque 259 * Output: An instance of the resource named by the URI. 260 * Errors: 261 o Malformed URI 262 o URI is syntactically valid but does not exist in any form. 263 o URI exists but there is no available output from this 264 operation. 265 o URI existed in the past but nothing is currently known 266 about it. 267 o Access denied 268 * Security Considerations: 269 o Malicious Redirection (see I2L) 270 o Denial of Service (see I2L) 272 This operation is used to return a single instance of the resource 273 that is named by the URI. The format of the output is dependent on the 274 resource itself. 276 4.4 I2Rs (URI to Resources) 278 * Name: URI to Resources 279 * Mnemonic: I2Rs 280 * Number of Operands: 1 281 * Type of Each Operand: First operand is a URI. 282 * Format of Each Operand: First operand is encoded as a URI. 283 * Algorithm: Opaque 284 * Output: Zero or more instances of the resource named by the URI. 285 * Errors: 286 o Malformed URI 287 o URI is syntactically valid but does not exist in any form. 288 o URI exists but there is no available output from this 289 operation. 290 o URI existed in the past but nothing is currently known 291 about it. 292 o Access denied 293 * Security Considerations: 294 o Malicious Redirection (see I2L) 295 o Denial of Service (see I2L) 297 This operation is used to return multiple instances of a resource, 298 for example, GIF and JPEG versions of an image. The judgment about the 299 resources being "the same" resides with the naming authority that 300 issued the URI. 302 The output shall be a MIME multipart/alternative [4] message with 303 the alternative versions of the resource in separate body parts. If 304 there is only one version of the resource identified by the URN, it MAY 305 be returned without the multipart/alternative wrapper. 307 4.5 I2C (URI to URC) 309 * Name: URI to URC 310 * Mnemonic: I2C 311 * Number of Operands: 1 312 * Type of Each Operand: First operand is a URI. 313 * Format of Each Operand: First operand is encoded as a URI. 314 * Algorithm: Opaque 315 * Output: A URC 316 * Errors: 317 o Malformed URI 318 o URI is syntactically valid but does not exist in any form. 319 o URI exists but there is no available output from this 320 operation. 321 o URI existed in the past but nothing is currently known 322 about it. 323 o Access denied 324 * Security Considerations: 325 o Malicious Redirection (see I2L) 326 o Denial of Service (see I2L) 328 Uniform Resource Characteristics are descriptions of resources. This 329 request allows the client to obtain a description of the resource 330 identified by a URI, as opposed to the resource itself or simply the 331 resource's URLs. The description might be a bibliographic citation, a 332 digital signature, or a revision history. This draft does not specify 333 the content of any response to a URC request. That content is expected 334 to vary from one server to another. 336 4.6 I2CS (URI to URCs) 338 * Name: URI to URCs 339 * Mnemonic: I2CS 340 * Number of Operands: 1 341 * Type of Each Operand: First operand is a URI. 342 * Format of Each Operand: First operand is encoded as a URI. 343 * Algorithm: Opaque 344 * Output: Zero or more URCs 345 * Errors: 346 o Malformed URI 347 o URI is syntactically valid but does not exist in any form. 348 o URI exists but there is no available output from this 349 operation. 350 o URI existed in the past but nothing is currently known 351 about it. 352 o Access denied 353 * Security Considerations: 354 o Malicious Redirection (see I2L) 355 o Denial of Service (see I2L) 357 URCs can come in different formats and types. This operation returns 358 zero or more URCs that are appropriate for the given URI. 360 4.7 I2N (URI to URN) 362 * Name: URI to URN 363 * Mnemonic: I2N 364 * Number of Operands: 1 365 * Type of Each Operand: First operand is a URN. 366 * Format of Each Operand: First operand is encoded as a URI. 367 * Algorithm: Opaque 368 * Output: One and only one URN 369 * Errors: 370 o Malformed URI 371 o URI is syntactically valid but does not exist in any form. 372 o URI exists but there is no available output from this 373 operation. 374 o URI existed in the past but nothing is currently known 375 about it. 376 o Access denied 377 * Security Considerations: 378 o Malicious Redirection (see I2L) 379 o Denial of Service (see I2L) 381 While URNs are supposed to identify one and only one resource, that 382 does not mean that a resource may have one and only one URN. For 383 example, consider a resource that one organization wishes to name 384 'foo'; another organization, in agreement with the first, wants to call 385 the resource 'bar'. Both organizations can agree that both names 'name' 386 the same resource and that the URNs 'foo' and 'bar' are equivalent. 388 The result is a URN, known to the server, that identifies the same 389 resource as the input URN. 391 Extreme care should be taken with this service as it toys with the 392 idea of equality with respect to URNs. As mentioned in several URN 393 documents, the idea of equality is very domain specific. For example, 394 a URN pointing to a weather map for a particular day and a URN pointing 395 to the map as it changes from day to day would NOT be returned in this 396 example because they point to do different resources. Some other concept 397 of temporary equivalence is at work. This service instead deals with 398 resources that have two different names where there is a binding 399 between the names that is agreed by both name assigners. I.e., both 400 namespaces MUST have agreed that the each name can be used in place of 401 the other and the meaning does not change. 403 4.8 I2Ns (URI to URNs) 405 * Name: URI to URNs 406 * Mnemonic: I2NS 407 * Number of Operands: 1 408 * Type of Each Operand: First operand is a URI. 409 * Format of Each Operand: First operand is encoded as a URI. 410 * Algorithm: Opaque 411 * Output: A list of URNs 412 * Errors: 413 o Malformed URI 414 o URI is syntactically valid but does not exist in any form. 415 o URI exists but there is no available output from this 416 operation. 417 o URI existed in the past but nothing is currently known 418 about it. 419 o Access denied 420 * Security Considerations: 421 o Malicious Redirection (see I2L) 422 o Denial of Service (see I2L) 424 This operation simply returns zero or more URNs following the same 425 criteria and cautions as the I2N operation. 427 4.9 I=I (Is URI equal to URI): 429 * Name: URI = URI 430 * Mnemonic: I=I 431 * Number of Operands: 2 432 * Type of Each Operand: Both operands are URIs. 433 * Format of Each Operand: Both operands are encoded as a URIs. 434 * Algorithm: Opaque 435 * Output: TRUE or FALSE 436 * Errors: 437 o Malformed URIs 438 o URIs are syntactically valid but do not exist in any form. 439 o URIs exist but there is no available output from this 440 operation. 441 o URIs existed in the past but nothing is currently known 442 about them. 443 o Access denied 444 * Security Considerations: 445 o Malicious Redirection (see I2L) 446 o Denial of Service (see I2L) 448 This operation is used to determine whether two given URIs are 449 considered to be equal by the server being asked the question. The 450 algorithm used to determine equality is opaque. No assertions are made 451 about whether or not the URIs exhibits characteristics of URNs or URLs. 453 5. The text/uri-list Internet Media Type 455 [This section will be augmented or replaced by the registration of 456 the text/uri-list IMT once that registration has been performed]. 458 Several of the resolution service requests, such as I2Ls, I2Ns, 459 result in a list of URIs being returned to the client. The 460 text/uri-list Internet Media Type is defined to provide a simple format 461 for the automatic processing of such lists of URIs. 463 The format of text/uri-list resources is as follows. 465 1. Any lines beginning with the '#' character are comment lines and 466 are ignored during processing. (Note that '#' is a character that 467 may appear in URIs, so it only denotes a comment when it is the 468 first character on a line.) 469 2. The remaining non-comment lines MUST be URIs (URNs or URLs), 470 encoded according to the URI specification RFC[3]. Each URI shall 471 appear on one and only one line. 472 3. As for all text/* formats, lines are terminated with a CR LF pair, 473 although clients should be liberal in accepting lines with only 474 one of those characters. 475 4. The order of the URIs given MUST be preserved upon retransmission. 476 The client should not make any inferences about what the order of 477 the returned list means. 479 In applications where one URI has been mapped to a list of URIs, 480 such as in response to the I2Ls request, the first line of the 481 text/uri-list response SHOULD be a comment giving the original URI. An 482 example of such a result for the I2L request is shown below in Figure 1. 484 ------------------------------------------ 486 # urn:cid:foo@huh.org 487 http://www.huh.org/cid/foo.html 488 http://www.huh.org/cid/foo.pdf 489 ftp://ftp.foo.org/cid/foo.txt 491 Figure 1: Example of the text/uri-list format 492 ------------------------------------------ 494 6. Security Considerations 496 Communications with a server may be of a sensitive nature. Some 497 servers will hold information that should only be released to 498 authorized users. The results from servers may be the target of 499 spoofing, especially once electronic commerce transactions are common 500 and there is money to be made by directing users to pirate repositories 501 rather than repositories that pay royalties to rights-holders. Server 502 requests may be of interest to traffic analysts. The requests may also 503 be subject to spoofing. 505 The "Access denied" error message assumes a system within which the 506 operation is being performed that can convey an authenticated concept 507 of access control. Thus, the "Access denied" message should only be 508 returned by systems that have an appropriate method of determining 509 access control. 511 7. References 513 [1] Daniel, R., and Mealling, M., "Resolution of Uniform Resource 514 Identifiers using the Domain Name System", RFC2168, February, 1997. 516 [2] R. Moats, "URN Syntax", RFC2141, January, 1997. 518 [3] Berners-Lee, T., "Universal Resource Identifiers in WWW: A Unifying 519 Syntax for the Expression of Names and Addresses of Objects on the 520 Network as Used in the World-Wide Web", RFC 1630, June, 1994. 522 [4] Borenstein, N. and Freed, N., "MIME (Multipurpose Internet Mail 523 Extensions) Part One: Mechanisms for Specifying and Describing the 524 Format of Internet Message Bodies", RFC 1521, Bellcore, Innosoft, 525 September, 1993. 527 [5] Sollins, K., draft-ietf-urn-req-frame-02, "Guidelines and a 528 Framework for URN Resolution Systems", MIT/LCS, June, 1997. 529 [Note to RFC Editor: Please change this reference to point to the 530 correct RFC number for the draft] 532 [6] Kunze, J., "Functional Recommendations for Internet Resource 533 Locators", RFC1736, IS&T, UC Berkeley, February, 1995. 535 [7] Berners-Lee, T., Masinter, L., McCahill, M., et al., "Uniform 536 Resource Locators (URL)", RFC1738, December, 1994. 538 8. Author Contact Information 540 Michael Mealling Ron Daniel 541 Network Solutions Advanced Computing Lab, MS B287 542 505 Huntmar Park Drive Los Alamos National Laboratory 543 Herndon, VA 22070 Los Alamos, NM, USA, 87545 544 voice: (703) 742-0400 voice: (505) 665-0597 545 fax: (703) 742-9552 fax: (505) 665-4939 546 email: michaelm@rwhois.net email: rdaniel@lanl.gov 548 This document expires 6 months from November, 1997