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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 November 1997 Ron Daniel Jr. 4 Intended category: Experimental Los Alamos National Laboratory 5 draft-ietf-urn-resolution-services-04.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 new ones to be written by others, the requirements below are 95 placed on any documents that seek to specify new operations. Any 96 specification of a member of this set of operations MUST contain at 97 least the following pieces of information with respect to its operands, 98 its algorithm, output, and errors. 100 At this stage it is unclear whether or not the registration of these 101 operations is required. In the future if it becomes apparent that these 102 functions are widely used and extended then some registration scheme 103 will need to be developed. 105 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 106 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 107 document are to be interpreted as described in RFC 2119. 109 2.1 Operands 111 Operands must contain the following pieces of information: 113 * name of the operation 114 * case insensitive mnemonic for the operation 115 * number of operands 116 * type of each operand 117 * format of each operand 119 2.2 Algorithm 121 The exact algorithm for the operation must be specified, or it must 122 be specified that the algorithm is opaque and defined by the server. 124 2.3 Output 126 Output must specify one of the following: 128 * there is no output 129 * the output is undefined 130 * the output itself and its content 131 * the fact that the output is an object and the object's 132 type and format 133 * any non-protocol specific errors 135 2.4 Error Conditions 137 All errors that are considered applicable across all implementations 138 and application environments must be included. Errors that depend on 139 the system conveying the service are not included. Thus, many of the 140 expected errors such as service availability or operation syntax are 141 not included in this document since they are implementation dependent. 143 2.5 Security Considerations 145 Any security considerations relating to the service provided must be 146 specified. This does NOT include considerations dealing with the 147 protocol used to convey the service or to those that normally accompany 148 the results of the service. For example, an I2L service would need to 149 discuss the situation where someone maliciously inserts an incorrect 150 URL into the resolver but NOT the case where someone sends personal 151 information across the Internet to the resource identified by the 152 correct URL. 154 3. Encoding The Operations 156 To be useful, these operations have to be used within some system or 157 protocol. In many cases, these systems and protocols will place 158 restrictions on which operations make sense and how those that do are 159 syntactically represented. It is sufficient for those protocols to 160 define new operations within their own protocol specification 161 documents but care should be taken to make this fact well known. 163 Also, a given system or protocol will have its own output formats 164 that will restrict the output formats of a given operation. 165 Additionally, a given protocol may have better solution for output 166 than the ones given here. For example, the I2L result may be 167 encoded in a protocol-specific manner that conveys information about 168 the closeness of each resource on the network. 170 Thus, the requirements on encoding these operations within a given 171 system are as follows: 173 * which subset of the operations are allowed 174 * how the operator is encoded 175 * how the operands are encoded 176 * how the error codes are returned 178 For those systems that can use it, MIME [4] is the suggested output 179 format. The operations listed here use the text/uri-list Internet Media 180 Type (IMT) [4] that is specified in Section 6. Other systems are 181 strongly encouraged to use this IMT. In the case where a system does 182 not use an IMT, a justification should be given. 184 4. The Incomplete Set 186 4.1 I2L (URI to URL) 188 * Name: URI to URL 189 * Mnemonic: I2L 190 * Number of Operands: 1 191 * Type of Each Operand: First operand is a URI. 192 * Format of Each Operand: First operand is encoded as a URI. 193 * Algorithm: Opaque 194 * Output: One and only one URL encoded in a text/uri-list 195 * Errors Conditions: 196 o Malformed URI 197 o URI is syntactically valid but does not exist in any form. 198 o URI exists but there is no available output from this 199 operation. 200 o URI existed in the past but nothing is currently known 201 about it. 202 o Access denied 204 * Security Considerations: 205 o Malicious Redirection 206 One of the fundamental dangers related to any service such as 207 this is that a malicious entry in a resolver's database will 208 cause clients to resolve the URI into the wrong URL. The 209 possible intent may be to cause the client to retrieve a 210 resource containing fraudulent or damaging material. 211 o Denial of Service 212 By removing the URL to which the URI maps, a malicious 213 intruder may remove the client's ability to retrieve the 214 resource. 216 This operation is used to map a single URI to a single URL. It is 217 used by lightweight clients that do not have the ability to select from 218 a list of URLs or understand a URC. The algorithm for this mapping is 219 dependent on the URI scheme. 221 4.2 I2Ls (URI to URLs) 223 * Name: URI to URLs 224 * Mnemonic: I2LS 225 * Number of Operands: 1 226 * Type of Each Operand: First operand is a URI. 227 * Format of Each Operand: First operand is encoded as a URI. 228 * Algorithm: Opaque 229 * Output: A list of zero or more URLs encoded in a text/uri-list 230 * Errors: 231 o Malformed URI 232 o URI is syntactically valid but does not exist in any form. 233 o URI exists but there is no available output from this 234 operation. 235 o URI existed in the past but nothing is currently known 236 about it. 237 o Access denied 238 * Security Considerations: 239 o Malicious Redirection (see I2L) 240 o Denial of Service (see I2L) 242 This operation is used to map a single URI to 0 or more URLs. It is 243 used by a client that can pick from a list of URLs based on some 244 criteria that are important to the client. The client should not make 245 any assumptions about the order of the URLs returned. No matter what 246 the particular media type, the result MUST be a list of the URLs that 247 may be used to obtain an instance of the resource identified by the 248 URI. All URIs shall be encoded according to the URI specification [3]. 250 4.3 I2R (URI to Resource) 252 * Name: URI to Resource 253 * Mnemonic: I2R 254 * Number of Operands: 1 255 * Type of Each Operand: First operand is a URI. 256 * Format of Each Operand: First operand is encoded as a URI. 257 * Algorithm: Opaque 258 * Output: An instance of the resource named by the URI. Encoding is 259 not specified. 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 Encoding is not specified but MIME multipart/alternative is 286 encouraged. 287 * Errors: 288 o Malformed URI 289 o URI is syntactically valid but does not exist in any form. 290 o URI exists but there is no available output from this 291 operation. 292 o URI existed in the past but nothing is currently known 293 about it. 294 o Access denied 295 * Security Considerations: 296 o Malicious Redirection (see I2L) 297 o Denial of Service (see I2L) 299 This operation is used to return multiple instances of a resource, 300 for example, GIF and JPEG versions of an image. The judgment about the 301 resources being "the same" resides with the naming authority that 302 issued the URI. 304 The output shall be a MIME multipart/alternative [4] message with 305 the alternative versions of the resource in separate body parts. If 306 there is only one version of the resource identified by the URN, it MAY 307 be returned without the multipart/alternative wrapper. 309 4.5 I2C (URI to URC) 311 * Name: URI to URC 312 * Mnemonic: I2C 313 * Number of Operands: 1 314 * Type of Each Operand: First operand is a URI. 315 * Format of Each Operand: First operand is encoded as a URI. 316 * Algorithm: Opaque 317 * Output: A URC. Encoding is not specified. 318 * Errors: 319 o Malformed URI 320 o URI is syntactically valid but does not exist in any form. 321 o URI exists but there is no available output from this 322 operation. 323 o URI existed in the past but nothing is currently known 324 about it. 325 o Access denied 326 * Security Considerations: 327 o Malicious Redirection (see I2L) 328 o Denial of Service (see I2L) 330 Uniform Resource Characteristics are descriptions of resources. This 331 request allows the client to obtain a description of the resource 332 identified by a URI, as opposed to the resource itself or simply the 333 resource's URLs. The description might be a bibliographic citation, a 334 digital signature, or a revision history. This draft does not specify 335 the content of any response to a URC request. That content is expected 336 to vary from one server to another. 338 4.6 I2CS (URI to URCs) 340 * Name: URI to URCs 341 * Mnemonic: I2CS 342 * Number of Operands: 1 343 * Type of Each Operand: First operand is a URI. 344 * Format of Each Operand: First operand is encoded as a URI. 345 * Algorithm: Opaque 346 * Output: Zero or more URCs. Encoding is not specified. 347 * Errors: 348 o Malformed URI 349 o URI is syntactically valid but does not exist in any form. 350 o URI exists but there is no available output from this 351 operation. 352 o URI existed in the past but nothing is currently known 353 about it. 354 o Access denied 355 * Security Considerations: 356 o Malicious Redirection (see I2L) 357 o Denial of Service (see I2L) 359 URCs can come in different formats and types. This operation returns 360 zero or more URCs that are appropriate for the given URI. 362 4.7 I2N (URI to URN) 364 * Name: URI to URN 365 * Mnemonic: I2N 366 * Number of Operands: 1 367 * Type of Each Operand: First operand is a URN. 368 * Format of Each Operand: First operand is encoded as a URI. 369 * Algorithm: Opaque 370 * Output: One URN encoded in a text/uri-list IMT. 371 * Errors: 372 o Malformed URI 373 o URI is syntactically valid but does not exist in any form. 374 o URI exists but there is no available output from this 375 operation. 376 o URI existed in the past but nothing is currently known 377 about it. 378 o Access denied 379 * Security Considerations: 380 o Malicious Redirection (see I2L) 381 o Denial of Service (see I2L) 383 While URNs are supposed to identify one and only one resource, that 384 does not mean that a resource may have one and only one URN. For 385 example, consider a resource that one organization wishes to name 386 'foo'; another organization, in agreement with the first, wants to call 387 the resource 'bar'. Both organizations can agree that both names 'name' 388 the same resource and that the URNs 'foo' and 'bar' are equivalent. 390 The result is a URN, known to the server, that identifies the same 391 resource as the input URN. The result shall be encoded in a 392 text/uri-list IMT. 394 Extreme care should be taken with this service as it toys with the 395 idea of equality with respect to URNs. As mentioned in several URN 396 documents, the idea of equality is very domain specific. For example, 397 a URN pointing to a weather map for a particular day and a URN pointing 398 to the map as it changes from day to day would NOT be returned in this 399 example because they point to do different resources. Some other concept 400 of temporary equivalence is at work. This service instead deals with 401 resources that have two different names where there is a binding 402 between the names that is agreed by both name assigners. I.e., both 403 namespaces must have agreed that the each name can be used in place of 404 the other and the meaning does not change. 406 4.8 I2Ns (URI to URNs) 408 * Name: URI to URNs 409 * Mnemonic: I2NS 410 * Number of Operands: 1 411 * Type of Each Operand: First operand is a URI. 412 * Format of Each Operand: First operand is encoded as a URI. 413 * Algorithm: Opaque 414 * Output: A list of URNs encoded in a text/uri-list IMT 415 * Errors: 416 o Malformed URI 417 o URI is syntactically valid but does not exist in any form. 418 o URI exists but there is no available output from this 419 operation. 420 o URI existed in the past but nothing is currently known 421 about it. 422 o Access denied 423 * Security Considerations: 424 o Malicious Redirection (see I2L) 425 o Denial of Service (see I2L) 427 This operation simply returns zero or more URNs following the same 428 criteria and cautions as the I2N operation. 430 4.9 I=I (Is URI equal to URI): 432 * Name: URI = URI 433 * Mnemonic: I=I 434 * Number of Operands: 2 435 * Type of Each Operand: Both operands are URIs. 436 * Format of Each Operand: Both operands are encoded as a URIs. 437 * Algorithm: Opaque 438 * Output: TRUE or FALSE 439 * Errors: 440 o Malformed URIs 441 o URIs are syntactically valid but do not exist in any form. 442 o URIs exist but there is no available output from this 443 operation. 444 o URIs existed in the past but nothing is currently known 445 about them. 446 o Access denied 447 * Security Considerations: 448 o Malicious Redirection (see I2L) 449 o Denial of Service (see I2L) 451 This operation is used to determine whether two given URIs are 452 considered to be equal by the server being asked the question. The 453 algorithm used to determine equality is opaque. No assertions are made 454 about whether or not the URIs exhibits characteristics of URNs or URLs. 456 5. The text/uri-list Internet Media Type 458 [This section will be augmented or replaced by the registration of 459 the text/uri-list IMT once that registration has been performed]. 461 Several of the resolution service requests, such as I2Ls, I2Ns, 462 result in a list of URIs being returned to the client. The 463 text/uri-list Internet Media Type is defined to provide a simple format 464 for the automatic processing of such lists of URIs. 466 The format of text/uri-list resources is as follows. 468 1. Any lines beginning with the '#' character are comment lines and 469 are ignored during processing. (Note that '#' is a character that 470 may appear in URIs, so it only denotes a comment when it is the 471 first character on a line.) 472 2. The remaining non-comment lines MUST be URIs (URNs or URLs), 473 encoded according to the URI specification RFC[3]. Each URI shall 474 appear on one and only one line. 475 3. As for all text/* formats, lines are terminated with a CR LF pair, 476 although clients should be liberal in accepting lines with only 477 one of those characters. 478 4. The order of the URIs given MUST be preserved upon retransmission. 479 The client should not make any inferences about what the order of 480 the returned list means. 482 In applications where one URI has been mapped to a list of URIs, 483 such as in response to the I2Ls request, the first line of the 484 text/uri-list response SHOULD be a comment giving the original URI. An 485 example of such a result for the I2L request is shown below in Figure 1. 487 ------------------------------------------ 489 # urn:cid:foo@huh.org 490 http://www.huh.org/cid/foo.html 491 http://www.huh.org/cid/foo.pdf 492 ftp://ftp.foo.org/cid/foo.txt 494 Figure 1: Example of the text/uri-list format 495 ------------------------------------------ 497 6. Security Considerations 499 Communications with a server may be of a sensitive nature. Some 500 servers will hold information that should only be released to 501 authorized users. The results from servers may be the target of 502 spoofing, especially once electronic commerce transactions are common 503 and there is money to be made by directing users to pirate repositories 504 rather than repositories that pay royalties to rights-holders. Server 505 requests may be of interest to traffic analysts. The requests may also 506 be subject to spoofing. 508 The "Access denied" error message assumes a system within which the 509 operation is being performed that can convey an authenticated concept 510 of access control. Thus, the "Access denied" message should only be 511 returned by systems that have an appropriate method of determining 512 access control. 514 7. References 516 [1] Daniel, R., and Mealling, M., "Resolution of Uniform Resource 517 Identifiers using the Domain Name System", RFC2168, February, 1997. 519 [2] R. Moats, "URN Syntax", RFC2141, January, 1997. 521 [3] Berners-Lee, T., "Universal Resource Identifiers in WWW: A Unifying 522 Syntax for the Expression of Names and Addresses of Objects on the 523 Network as Used in the World-Wide Web", RFC 1630, June, 1994. 525 [4] Borenstein, N. and Freed, N., "MIME (Multipurpose Internet Mail 526 Extensions) Part One: Mechanisms for Specifying and Describing the 527 Format of Internet Message Bodies", RFC 1521, Bellcore, Innosoft, 528 September, 1993. 530 [5] Sollins, K., draft-ietf-urn-req-frame-02, "Guidelines and a 531 Framework for URN Resolution Systems", MIT/LCS, June, 1997. 532 [Note to RFC Editor: Please change this reference to point to the 533 correct RFC number for the draft] 535 [6] Kunze, J., "Functional Recommendations for Internet Resource 536 Locators", RFC1736, IS&T, UC Berkeley, February, 1995. 538 [7] Berners-Lee, T., Masinter, L., McCahill, M., et al., "Uniform 539 Resource Locators (URL)", RFC1738, December, 1994. 541 8. Author Contact Information 543 Michael Mealling Ron Daniel 544 Network Solutions Advanced Computing Lab, MS B287 545 505 Huntmar Park Drive Los Alamos National Laboratory 546 Herndon, VA 22070 Los Alamos, NM, USA, 87545 547 voice: (703) 742-0400 voice: (505) 665-0597 548 fax: (703) 742-9552 fax: (505) 665-4939 549 email: michaelm@rwhois.net email: rdaniel@lanl.gov 551 This document expires 6 months from November, 1997