idnits 2.17.1 draft-freed-sieve-notary-08.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** You're using the IETF Trust Provisions' Section 6.b License Notice from 12 Sep 2009 rather than the newer Notice from 28 Dec 2009. (See https://trustee.ietf.org/license-info/) Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (May 3, 2010) is 5078 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'COMPARATOR' is mentioned on line 263, but not defined == Missing Reference: 'ADDRESS-PART' is mentioned on line 263, but not defined == Missing Reference: 'MATCH-TYPE' is mentioned on line 264, but not defined -- Obsolete informational reference (is this intentional?): RFC 3501 (Obsoleted by RFC 9051) Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group N. Freed 3 Internet-Draft Oracle 4 Intended status: Standards Track May 3, 2010 5 Expires: November 4, 2010 7 Sieve Email Filtering: Delivery Status Notifications and Deliver-By 8 Extensions 9 draft-freed-sieve-notary-08 11 Abstract 13 This document describes the "envelope-dsn", "redirect-dsn", 14 "envelope-deliverby", and "redirect-deliverby" extensions to the 15 Sieve email filtering language. The "envelope-dsn" and "envelope- 16 deliverby" extensions provide access to additional envelope 17 information provided by the delivery status notification and 18 deliver-by SMTP extensions, respectively. The "redirect-dsn" and 19 "redirect-deliverby" extensions extend Sieve's redirect action to 20 provide control over delivery status notification and deliver-by 21 parameters, respectively. 23 Change History (to be removed prior to publication as an RFC 25 Correct RFC 2852 section reference. 27 Removed some extraneous [ characters from a couple of figures. 29 Clarified orcpt decoding. 31 Changed the ABNF for notary values to disallow spaces. 33 Fixed several typos. 35 Changed name of extension from notary to envelope-dsn. 37 Added the redirect-dsn extension. 39 Updated references. 41 Added a note about the use of ADDRESS-PART arguments with the new 42 envelope-part strings defined by the envelope-dsn extension. 44 Fleshed out the redirect-dsn extension. 46 Changed document title to agree with new extension names. 48 Added some examples. 50 Fixed more typos. 52 Changed dsn-envelope and dsn-redirect to envelope-dsn and redirect- 53 dsn, respectively. 55 Added a redirect-dsn example. 57 Added the two deliver-by extensions. 59 Added requirements text regarding envelope sender address selection. 61 Added various clarifications about negative by-time values. 63 Added a pointer to the conventions section to where Sieve errors are 64 discussed. 66 Clearified test failure text in both envelope extensions. 68 Addeed the ability to deal with by-times as either absolute ISO 8601 69 or relative integer values. 71 Status of this Memo 73 This Internet-Draft is submitted to IETF in full conformance with the 74 provisions of BCP 78 and BCP 79. 76 Internet-Drafts are working documents of the Internet Engineering 77 Task Force (IETF), its areas, and its working groups. Note that 78 other groups may also distribute working documents as Internet- 79 Drafts. 81 Internet-Drafts are draft documents valid for a maximum of six months 82 and may be updated, replaced, or obsoleted by other documents at any 83 time. It is inappropriate to use Internet-Drafts as reference 84 material or to cite them other than as "work in progress." 86 The list of current Internet-Drafts can be accessed at 87 http://www.ietf.org/ietf/1id-abstracts.txt. 89 The list of Internet-Draft Shadow Directories can be accessed at 90 http://www.ietf.org/shadow.html. 92 This Internet-Draft will expire on November 4, 2010. 94 Copyright Notice 96 Copyright (c) 2010 IETF Trust and the persons identified as the 97 document authors. All rights reserved. 99 This document is subject to BCP 78 and the IETF Trust's Legal 100 Provisions Relating to IETF Documents 101 (http://trustee.ietf.org/license-info) in effect on the date of 102 publication of this document. Please review these documents 103 carefully, as they describe your rights and restrictions with respect 104 to this document. Code Components extracted from this document must 105 include Simplified BSD License text as described in Section 4.e of 106 the Trust Legal Provisions and are provided without warranty as 107 described in the BSD License. 109 1. Introduction 111 Sieve [RFC5228] is a language for filtering email messages at or 112 around the time of final delivery. It is designed to be 113 implementable on either a mail client or mail server. It is suitable 114 for running on a mail server where users may not be allowed to 115 execute arbitrary programs, such as on black box Internet Message 116 Access Protocol [RFC3501] servers, as it has no user-controlled loops 117 or the ability to run external programs. 119 The base sieve specification defines the envelope extension and test 120 to access information in the message envelope. Only information 121 available in regular SMTP [RFC5321] is provided; additional 122 information added to the SMTP envelope by SMTP extensions cannot be 123 accessed. 125 The "envelope-dsn" extension extends the envelope test to allow 126 access to the additional envelope fields defined by the SMTP 127 extension for delivery status notification specified in RFC 3461 128 [RFC3461]. The "envelope-deliverby" extension extends the envelope 129 test to allow access to the additional envelope fields defined by the 130 deliver-by SMTP extension defined in [RFC2852]. 132 The base sieve specification also defines the redirect action, which 133 sends the message to a different address. Redirect only allows 134 specification of the new recipient address. The "redirect-dsn" 135 extension extends redirect to allow specification of some fields 136 defined by the delivery status notification SMTP extension. 137 "redirect-deliverby" in turn provides the ability to set a time limit 138 for delivery as specified in RFC 2852 [RFC2852]. 140 2. Conventions used in this document 142 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 143 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 144 document are to be interpreted as described in [RFC2119]. 146 The terms used to describe the various components of the Sieve 147 language are taken from Section 1.1 of [RFC5228]. The nature and 148 handling of Sieve errors is described in Section 2.10.6. 150 This document uses the ABNF notation specified in [RFC5234], and 151 refers to the ABNF productions notify-esmtp-value defined in Section 152 4.1 of [RFC3461]. 154 3. Capability Identifiers 156 The capability strings associated with the extensions defined in this 157 document are "envelope-dsn", "redirect-dsn", "envelope-deliverby", 158 and "redirect-deliverby". 160 4. Envelope-dsn Extension 162 The "envelope-dsn" extension does not define any new tests or 163 actions, rather, it adds four values to the list of possible (case- 164 insensitive) envelope-part strings defined in Section 5.4 of 165 [RFC5228]: 167 notify - Match the list of notification conditions, or NOTIFY 168 values, associated with the TO address used in the SMTP RCPT TO 169 command that resulted in this message getting delivered to this 170 user. More than one notification condition can be in effect at 171 once; each condition that is in effect is tested separately and 172 any match causes the test to succeed. The syntax and semantics of 173 the NOTIFY parameter are defined in Section 4.1 of RFC 3461 174 [RFC3461] . Currently the possible notification condition values 175 are "NEVER", "SUCCESS", "FAILURE" and "DELAY". Note that the 176 value "NEVER" is never combined with any other value. 178 orcpt - Match the original recipient, or ORCPT, value associated 179 with the TO address used in the SMTP RCPT TO command that resulted 180 in this message getting delivered to this user, with xtext 181 encoding removed. The syntax and semantics of the ORCPT parameter 182 are defined in Section 4.2 of RFC 3461 [RFC3461]. 184 ret - Match the return of content, or RET, value given in the SMTP 185 MAIL FROM command. The syntax and semantics of the RET parameter 186 are defined in Section 4.3 of RFC 3461 [RFC3461]. The possible 187 return of content values are "FULL" and "HDRS". 189 envid - Match the envelope identifier, or ENVID, value in decoded 190 form given in the SMTP MAIL FROM command. The syntax and 191 semantics of the ENVID parameter are defined in Section 4.4 of RFC 192 3461 [RFC3461]. 194 The envelope test fails unconditionally for each of these envelope- 195 part strings if the specified envelope parameter does not exist for 196 the current message or recipient. 198 The envelope test's ADDRESS-PART argument assumes the string being 199 tested has the syntax of an email address. None of the new envelope 200 parts defined here have address syntax, accordingly, it is an error 201 to specify an ADDRESS-PART argument in conjunction with these new 202 envelope parts. 204 The "relational" extension [RFC5231] adds a match type called 205 ":count". The count of an envelope test with an envelope-part of 206 "orcpt", "ret", and "envid" is 1 if the corresponding SMTP parameter 207 is present and 0 otherwise. The count of an envelope test with an 208 envelope-part of "notify" is equal to the number of notification 209 conditions specified and 0 if the NOTIFY parameter is not present. 211 4.1. Examples 213 The fact that the NOTIFY envelope parameter is multivalued and the 214 notify envelope-part turns this into a list of values makes it easy 215 to check to see if a given value is present without having to worry 216 about other values: 218 require ["envelope", "envelope-dsn"]; 220 # Check whether SUCCESS notifications were requested, 221 # irrespective of any other requests that were made 222 if envelope "notify" "SUCCESS" 223 { 224 # do whatever 225 } 227 Checking to see if a given request is the only one present is a 228 little trickier, however: 230 require ["envelope", "envelope-dsn", "relational", 231 "comparator-i;ascii-numeric"]; 233 # Check whether only FAILURE notifications were requested 234 if allof ( envelope "notify" "FAILURE", 235 envelope :comparator "i;ascii-numeric" 236 :count "eq" "notify" "1" 237 ) 238 { 239 # do whatever 240 } 242 The orcpt envelope-part always contains an address type indicator 243 prefix in addition to an address, which must be taken into account in 244 any tests: 246 require ["envelope", "envelope-dsn"]; 248 # See if the orcpt is an RFC822 address in the example.com 249 # domain 250 if envelope :matches "orcpt" "rfc822;*@example.com" 251 { 252 # do whatever 253 } 255 5. Envelope-deliverby Extension 257 The "envelope-deliverby" extension does not define any new tests or 258 actions, rather, it adds four values to the list of possible (case- 259 insensitive) envelope-part strings defined in Section 5.4 of 260 [RFC5228] and an optional :zone tagged argument. This updates the 261 usage description for envelope to: 263 Usage: envelope [COMPARATOR] [ADDRESS-PART] 264 [MATCH-TYPE] [:zone ] 265 266 268 These new envelope parts correspond to the new MAIL FROM parameters 269 defined in Section 4 of [RFC2852]. They are: 271 bytimeabsolute - Match the current value of the initial integer part 272 of the deliver-by extension's BY parameter on the SMTP MAIL FROM 273 command, converted into an absolute time represented in restricted 274 ISO 8601 format. The restricted ISO 8601 format is specified by 275 the date-time ABNF production given in [RFC3339], Section 5.6, 276 with the added restrictions that the letters "T" and "Z" MUST be 277 in upper case, and a time zone offset of zero MUST be represented 278 by "Z" and not "+00:00". 280 bytimerelative - Match the current value of the initial integer part 281 of the deliver-by extension's BY parameter specified in the SMTP 282 MAIL FROM command. 284 bymode - Match a string computed from the by-mode part of the 285 deliver-by extension's BY parameter. The possible values are 286 "notify" and "return", which correspond to the BY parameter mode 287 specifier characters "N" and "R" respectively. 289 bytrace - Match the trace modifier computed from the by-trace 290 modifier on the deliver-by extension's BY parameter. The possible 291 values are "trace" and "" (the empty string). These values 292 correspond to the presence or absence of the by-trace "T" modifier 293 respectively. 295 The envelope test fails unconditionally for each of these envelope- 296 part strings if the BY SMTP MAIL FROM parameter does not exist for 297 the current message or recipient. 299 The new :zone argument specifies a time zone offset string that any 300 bytimeabsolute value is to be shifted to prior to testing. :zone has 301 no effect on envelope-parts other than bytimeabsolute. The value of 302 time zone offset string MUST be an offset relative to UTC with the 303 following syntax: 305 time-zone = ( "+" / "-" ) 4DIGIT 307 The "+" or "-" indicates whether the time-of-day is ahead of (i.e., 308 east of) or behind (i.e., west of) UTC. The first two digits 309 indicate the number of hours difference from Universal Time, and the 310 last two digits indicate the number of minutes difference from 311 Universal Time. Note that this agrees with the RFC 2822 format for 312 time zone offsets, not the ISO 8601 format. The local time zone MUST 313 be used for bytimeabsolute if the :zone argument is omitted. 315 The envelope test's ADDRESS-PART argument assumes the string being 316 tested has the syntax of an email address. None of the new envelope 317 parts defined here have address syntax, accordingly, it is an error 318 to specify an ADDRESS-PART argument in conjunction with these new 319 envelope parts. 321 The "relational" extension [RFC5231] adds a match type called 322 ":count". The count of an envelope test with an envelope-part of 323 "bytime", "bymode", and "bytrace" is 1 if the BY parameter is present 324 and 0 otherwise. 326 It is important to note that the deliver-by by-time is decremented as 327 the message passes through the transport infrastructure. 328 Accordingly, it is not possible to tell what the message originator 329 set the value to, only the amount of time remaining at the moment the 330 sieve is run. Additionally, note that bytimerelative values can be 331 negative, making it necessary to either perform additional checks or 332 else use a comparator which, unlike i;ascii-numeric, is capable of 333 handling signed integers. 335 5.1. Example 337 As noted above, this extension does not provide access to the 338 originator's initial by-time setting for the simple reason that this 339 information is not part of the envelope. It can, however, be used to 340 check and see if the message was delivered within the alloted time. 341 Note the additional check to see if the value is negative. 343 require ["envelope", "envelope-deliverby", "relational", 344 "comparator-i;ascii-numeric"]; 346 # Check to see if this message didn't make it in the time alloted by 347 # the originator. 348 if anyof (envelope :contains "bytimerelative" "-", 349 envelope :value "eq" :comparator "i;ascii-numeric" 350 "bytimerelative" "0") 351 { 352 # do whatever 353 } 355 This operation can be done more simply if the date and variables 356 extensions are available: 358 require ["envelope", "envelope-deliverby", "relational", "date" 359 "variables"]; 361 # Check to see if this message didn't make it in the time alloted by 362 # the originator. 363 if currentdate :matches "iso8601" "*" { 364 set "cdate" "${0}"; 365 if envelope :value "ge" "bytimeabsolute" "${cdate}") 366 { 367 # do whatever 368 } 369 } 371 6. redirect-dsn extension 373 The "redirect-dsn" extension does not define any new tests or 374 actions, rather, it adds two new arguments, NOTIFY and RET, to the 375 redirect action defined in Section 4.2 of [RFC5228]. This updates 376 the usage description for redirect to: 378 Usage: redirect [:notify "value"] [:ret "FULL"|"HDRS"] 379 381 The syntax for the NOTIFY and RET arguments are: 383 NOTIFY = ":notify" notify-value 384 notify-value = DQUOTE ("NEVER" / notify-esmtp-list) DQUOTE 385 notify-esmtp-list = notify-list-element *("," notify-list-element) 387 RET = ":ret" ret-value 388 ret-value = DQUOTE ("FULL" / "HDRS") DQUOTE 390 The notify-list-element production is defined in Section 4.1 of 391 [RFC3461]. 393 When these arguments are specified, they set the corresponding NOTIFY 394 ESMTP RCPT TO and RET ESMTP MAIL FROM parameters, respectively. 395 These arguments are only honored if the delivery status notification 396 (DSN) ESMTP extension is available. When the DSN extension is not 397 available, these arguments MUST be ignored and MUST NOT cause an 398 error. 400 6.1. MAIL FROM address selection 402 RFC 5228 does not require any particular envelope sender address be 403 associated with redirected messages. However, the redirect-dsn 404 extension isn't terribly useful if the place where the delivery 405 status notifications are sent isn't known. Accordingly, when either 406 :notify or :ret is specified and the envelope sender address isn't 407 empty, implementations MUST set the envelope sender address to the 408 address of the sieve owner. 410 6.2. Example 412 One possible use of :notify on redirect is to combine the copy 413 extension [RFC3894] with the ability to suppress nondelivery 414 notifications to generate a private copy of selected messages with no 415 side effects or error notifications: 417 require ["copy", "redirect-dsn"]; 419 # Make a private copy of messages from user@example.com 420 if address "from" "user@example.com" 421 { 422 redirect :copy :notify "NEVER" "elsewhere@example.com"; 423 } 425 7. redirect-deliverby extension 427 The "redirect-deliverby" extension does not define any new tests or 428 actions, rather, it adds three new arguments, BYTIME, BYMODE, and 429 BYTRACE, to the redirect action defined in Section 4.2 of [RFC5228]. 430 This updates the usage description for redirect to: 432 Usage: redirect [:bytimerelative / 433 :bytimeabsolute 434 [:bymode "notify"|"return"] [:bytrace]] 435 437 :bytimerelative specifies the number of seconds within which the 438 message should be delivered. This parameter does not allow 439 specification of negative values; it should not be necessary specify 440 such values in this context. :bytimeabsolute specifies an absolute 441 time limit on delivery. The limit in this case is specified in the 442 restricted ISO 8601 format specified by the date-time ABN production 443 given in [RFC3339] 445 :bymode specifies whether a notification should be sent or the 446 message simply returned if the time limit is exceeded. The default 447 is "return" if :bymode is not specified. :bytrace, if specified, 448 activiates message tracing. 450 The semantics of delivery time limits and these parameters are 451 specified and discussed at length in [RFC2852]. 453 It is an error to specify either :bymode or :bytrace without either 454 :bytimeabsolute or :bytimerelative. 456 When these arguments are specified, they are used to construct the 457 corresponding BY ESMTP MAIL FROM parameter. The :bytimeabsolute or 458 :bytimerelative value becomes the by-time, the :bymode becomes the 459 by-mode value, and :bytrace sets the by-trace modifier. If the 460 deliver-by extension is unavailable, the handling of reredirected 461 message MUST conform to the semantics specified in [RFC2852] section 462 4.1.4 for relaying to a server that does not support the deliver-by 463 SMTP extension. 465 7.1. MAIL FROM address selection 467 RFC 5228 does not require any particular envelope sender address be 468 associated with redirected messages. However, the redirect-deliverby 469 extension, like the redirect-dsn extension, isn't terribly useful if 470 the place where any delivery status notifications are sent isn't 471 known. Accordingly, when :bymode is specified and the envelope 472 sender address isn't empty, implementations MUST set the envelope 473 sender address to the address of the sieve owner. 475 7.2. Example 477 The obvious use of "redirect-deliverby" is to specify a limit on 478 delivery attempts for a redirected message: 480 require ["copy", "redirect-deliverby"]; 482 # Send a copy to my cell phone, time out after 10 minutes 483 if address "from" "user@example.com" 484 { 485 redirect :copy :bytimerelative 600 "cellphone@example.com"; 486 } 488 Limits on delivery after a particular time of day may also be 489 constructed: 491 require ["copy", "redirect-deliverby", "date", "variables", 492 "relational", "comparator-i;ascii-numeric"]; 494 # Send a copy to my cell phone to be delivered before 10PM 495 if currentdate :value "lt" 496 :comparator "i;ascii-numeric" "hour" "22" 497 { 498 if currentdate :matches "date" "*" {set "date" "${0}";} 499 if currentdate :matches "zone" "*" {set "zone" "${0}";} 500 redirect :copy :bytimeabsolute "${date}T20:00:00${zone}" 501 :bymode "return" "cellphone@example.com"; 502 } 504 8. Security Considerations 506 The envelope-dsn and envelope-deliverby extensions provide access to 507 additional message envelope information. This is not believed to 508 raise any additional security issues beyond those for the Sieve 509 "envelope" test. 511 The redirect-dsn extension allows specification of the delivery 512 status notification's NOTIFY parameter which can cause the generation 513 of notification messages that might otherwise not be generated, 514 especially if notification in the event of successful delivery is 515 required. Sites which limit the ability to request success 516 notifications will also need to restrict the ability to request them 517 using the redirect-dsn extension. 519 Similarly, the redirect-deliverby extension is used to control how 520 long the transport infrastructure will continue to attempt to deliver 521 a message before giving up, which could result in the generation of 522 additional notification messages. While the underlying Deliver-By 523 extension does have a minimum by-time limit, sites may wish to impose 524 additional limits on the minimum by-time allowed in a redirect 525 action. 527 All of the security considerations given in the base Sieve 528 specification also apply to this extension. 530 9. IANA Considerations 532 The following template specifies the IANA registration of the Sieve 533 extension specified in this document: 535 To: iana@iana.org 536 Subject: Registration of new Sieve extensions 538 Capability name: envelope-dsn 539 Description: The "envelope-dsn" extension extends the envelope 540 test to allow checking of information associated 541 with the DSN ESMTP extension defined in RFC 3461. 542 RFC number: RFC XXXX 543 Contact address: Sieve discussion list 545 Capability name: envelope-deliverby 546 Description: The "envelope-deliverby" extension extends the 547 envelope test to allow checking of information 548 associated with the Deliver-By ESMTP extension 549 defined in RFC 2852. 550 RFC number: RFC XXXX 551 Contact address: Sieve discussion list 553 Capability name: redirect-dsn 554 Description: The "redirect-dsn" extension extends the redirect 555 action to allow specification of the NOTIFY and 556 RET ESMTP parameters associated with the DSN SMTP 557 extension defined in RFC 3461. 558 RFC number: RFC XXXX 559 Contact address: Sieve discussion list 561 Capability name: redirect-deliverby 562 Description: The "redirect-deliverby" extension extends the 563 redirect action to allow specification of the BY 564 ESMTP parameter associated with the Deliver-By SMTP 565 extension defined in RFC 2852. 566 RFC number: RFC XXXX 567 Contact address: Sieve discussion list 569 This information should be added to the list of sieve extensions 570 given on http://www.iana.org/assignments/sieve-extensions. 572 10. References 573 10.1. Normative references 575 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 576 Requirement Levels", BCP 14, RFC 2119, March 1997. 578 [RFC2852] Newman, D., "Deliver By SMTP Service Extension", RFC 2852, 579 June 2000. 581 [RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the 582 Internet: Timestamps", RFC 3339, July 2002. 584 [RFC3461] Moore, K., "Simple Mail Transfer Protocol (SMTP) Service 585 Extension for Delivery Status Notifications (DSNs)", 586 RFC 3461, January 2003. 588 [RFC5228] Guenther, P. and T. Showalter, "Sieve: An Email Filtering 589 Language", RFC 5228, January 2008. 591 [RFC5231] Segmuller, W. and B. Leiba, "Sieve Email Filtering: 592 Relational Extension", RFC 5231, January 2008. 594 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 595 Specifications: ABNF", STD 68, RFC 5234, January 2008. 597 [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, 598 October 2008. 600 10.2. Informative references 602 [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 603 4rev1", RFC 3501, March 2003. 605 [RFC3894] Degener, J., "Sieve Extension: Copying Without Side 606 Effects", RFC 3894, October 2004. 608 Appendix A. Acknowledgements 610 Cyrus Daboo, Derek Diget, Philip Guenther, Arnt Gulbrandsen, Tero 611 Kivinen, Barry Leiba, Andrew McKeon, Alexey Melnikov, Chris Newman, 612 Aaron Stone, and Alexandros Vellis provided helpful suggestions and 613 corrections. 615 Author's Address 617 Ned Freed 618 Oracle 619 800 Royal Oaks 620 Monrovia, CA 91016-6347 621 USA 623 Phone: +1 909 457 4293 624 Email: ned.freed@mrochek.com