Date and Time on the Internet: Timestamps with additional information
draft-ietf-sedate-datetime-extended-01

Serialising Extended Data About Times and Events               U. Sharma
Internet-Draft                                              Igalia, S.L.
Intended status: Standards Track                              C. Bormann
Expires: 23 April 2022                            Universität Bremen TZI
                                                         20 October 2021

 Date and Time on the Internet: Timestamps with additional information
                 draft-ietf-sedate-datetime-extended-01

Abstract

   This document defines an extension to the timestamp format defined in
   RFC3339 for representing additional information including a time
   zone.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 23 April 2022.

Copyright Notice

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Extended Date/Time format . . . . . . . . . . . . . . . . . .   4
     3.1.  Informative . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Namespaced  . . . . . . . . . . . . . . . . . . . . . . .   4
     3.3.  Multi-character Namespaces  . . . . . . . . . . . . . . .   5
     3.4.  Syntax Extensions to RFC 3339 . . . . . . . . . . . . . .   7
     3.5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Dates and times are used in a very diverse set of internet
   applications, all the way from server-side logging to calendaring and
   scheduling.

   Each distinct instant in time can be represented in a descriptive
   text format using a timestamp, and [ISO8601] standardizes a widely-
   adopted timestamp format, which forms the basis of [RFC3339].
   However, this format only allows timestamps to contain very little
   additional relevant information, which means that, beyond that, any
   contextual information related to a given timestamp needs to be
   either handled separately or attached to it in a non-standard manner.

   This is already a pressing issue for applications that handle each
   instant with an associated time zone name, to take into account
   things like DST transitions.  Most of these applications attach the
   timezone to the timestamp in a non-standard format, at least one of
   which is fairly well-adopted [JAVAZDT].  Furthermore, applications
   might want to attach even more information to the timestamp,
   including but not limited to the calendar system it needs to be
   represented in.

   This document defines an extension syntax for timestamps as specified
   in [RFC3339] that has the following properties:

   *  The extension suffix is completely optional, making existing
      [RFC3339] timestamps compatible with this format.

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   *  The format is compatible with the pre-existing popular syntax for
      attaching time zone names to timestamps ([JAVAZDT]).

   *  The format provides a generalized way to attach any additional
      information to the timestamp.

2.  Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   UTC:  Coordinated Universal Time, as maintained since 1988 by the
      Bureau International des Poids et Mesures (BIPM) in conjunction
      with leap seconds as announced by the International Earth Rotation
      and Reference Frames Service [IERS].  From 1972 through 1987 UTC
      was maintained entirely by Bureau International de l'Heure (BIH).
      Before 1972 UTC was not generally recognized and civil time was
      determined by individual jurisdictions using different techniques
      for attempting to follow Universal Time based on measuring the
      rotation of the earth.

      UTC is often mistakenly referred to as GMT, an earlier time scale
      UTC was designed to be a useful successor for.

   ABNF:  Augmented Backus-Naur Form, a format used to represent
      permissible strings in a protocol or language, as defined in
      [RFC5234].  The rules defined in Appendix B of [RFC5234] are
      imported implictly.

   Internet Date/Time Format:  The date/time format defined in section 3
      of this document.

   Timestamp:  This term is used in this document to refer to an
      unambiguous representation of some instant in time.

   Z:  A suffix which, when applied to a time, denotes a UTC offset of
      00:00; often spoken "Zulu" from the ICAO phonetic alphabet
      representation of the letter "Z".

   Time Zone:  A time zone that is a included in the Time Zone Database
      (often called tz or zoneinfo) maintained by IANA.

   CLDR:  Common locale data repository [CLDR], a project of the Unicode
      Consortium to provide locale data to applications.

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   For more information about time scales, see Appendix E of [RFC1305],
   Section 3 of [ISO8601], and the appropriate ITU documents
   [ITU-R-TF.460-6].

3.  Extended Date/Time format

   This section discusses desirable qualities of formats for the
   timestamp extension suffix and defines such a format that extends
   [RFC3339] for use in Internet protocols.

3.1.  Informative

   The format should allow implementations to specify additional
   important information in addition to the bare timestamp.  This is
   done by defining _tags_, each with a _key_ and a _value_ separated by
   an equals sign, and allowing implementations to include an
   informative _suffix_ at the end with as many tags as required.  The
   value of a tag can be a hyphen delimited list of multiple values.

   In case a key is repeated or conflicted, implementations MUST give
   precedence to whichever value is positioned first.

3.2.  Namespaced

   Since tags can include all sorts of additional information, different
   standards bodies/organizations need a way to identify which part
   adheres to their standards.  For this, all information needs to be
   namespaced.  Each key is therefore divided into two hyphen-separated
   sections: the namespace and the key.  For example, the calendar as
   defined by the Unicode consortium could be included as u-ca=<value>.

   All single-character namespaces are reserved for [BCP47] extensions
   recorded in the BCP47 extensions registry.  For these namespaces:

   *  Case differences are ignored.

   *  The namespace is restricted to single alphanum, corresponding to
      extension singletons ('x' can be used for a private use
      extension).

   *  In addition, for CLDR extensions:

      -  There must be a namespace-key and it is restricted to 2
         alphanum characters.

      -  A suffix-value is limited to 3*8alphanum.

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3.3.  Multi-character Namespaces

   Multi-character namespaces can be registered specifically for use in
   this format, see Section 4.  The registration policy requires the
   development of an RFC, which SHALL define the name, purpose,
   processes, and procedures for maintaining the tags using the
   namespace registered.

   (This subsection uses BCP 14 language to describe the requirements on
   the information interchanged indirectly by providing requirements on
   the RFC registering a namespace and the principles of its evolution.)

   The maintaining or registering authority, including name, contact
   email, discussion list email, and URL location of the registry, MUST
   be indicated clearly in the RFC.  The RFC MUST specify each of the
   following (directly or included by reference):

   *  The specification MUST reference the specific version or revision
      of this document that governs its creation and MUST reference this
      section of this document.

   *  The specification and all keys defined by the specification MUST
      follow the ABNF and other rules for the formation of keys as
      defined in this document.  In particular, it MUST specify that
      case is not significant and that keys MUST NOT exceed eight
      characters in length.

   *  The specification MUST specify a canonical representation.

   *  The specification of valid keys MUST be available over the
      Internet and at no cost.

   *  The specification MUST be in the public domain or available via a
      royalty-free license acceptable to the IETF and specified in the
      RFC.

   *  The specification MUST be versioned, and each version of the
      specification MUST be numbered, dated, and stable.

   *  The specification MUST be stable.  That is, namespace keys, once
      defined by a specification, MUST NOT be retracted or change in
      meaning in any substantial way.

   *  The specification MUST include, in a separate section, the
      registration form reproduced in this section (below) to be used in
      registering the namespace upon publication as an RFC.

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   *  IANA MUST be informed of changes to the contact information and
      URL for the specification.

   IANA will maintain a registry of allocated multi-character
   namespaces.  This registry MUST use the record-jar format described
   by the ABNF in [BCP47].  Upon publication of a namespace as an RFC,
   the maintaining authority defined in the RFC MUST forward this
   registration form to <mailto:iesg@ietf.org>, who MUST forward the
   request to <mailto:iana@iana.org>.  The maintaining authority of the
   namespace MUST maintain the accuracy of the record by sending an
   updated full copy of the record to <mailto:iana@iana.org> with the
   subject line "TIMESTAMP FORMAT NAMESPACE UPDATE" whenever content
   changes.  Only the 'Comments', 'Contact_Email', 'Mailing_List', and
   'URL' fields MAY be modified in these updates.

   Failure to maintain this record, maintain the corresponding registry,
   or meet other conditions imposed by this section of this document MAY
   be appealed to the IESG [RFC2028] under the same rules as other IETF
   decisions (see [RFC2026]) and MAY result in the authority to maintain
   the extension being withdrawn or reassigned by the IESG.

   %%
   Identifier:
   Description:
   Comments:
   Added:
   RFC:
   Authority:
   Contact_Email:
   Mailing_List:
   URL:
   %%

       Figure 1: Registration record for a multi-character namespace

   'Identifier' contains the multi-character sequence assigned to the
   namespace.  The Internet-Draft submitted to define the namespace
   SHOULD specify which sequence to use, although the IESG MAY change
   the assignment when approving the RFC.

   'Description' contains the name and description of the namespace.

   'Comments' is an OPTIONAL field and MAY contain a broader description
   of the namespace.

   'Added' contains the date the namespace's RFC was published in the
   "date-full" format specified in Figure 2.  For example: 2004-06-28
   represents June 28, 2004, in the Gregorian calendar.

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   'RFC' contains the RFC number assigned to the namespace.

   'Authority' contains the name of the maintaining authority for the
   namespace.

   'Contact_Email' contains the email address used to contact the
   maintaining authority.

   'Mailing_List' contains the URL or subscription email address of the
   mailing list used by the maintaining authority.

   'URL' contains the URL of the registry for this namespace.

   The determination of whether an Internet-Draft meets the above
   conditions and the decision to grant or withhold such authority rests
   solely with the IESG and is subject to the normal review and appeals
   process associated with the RFC process.

3.4.  Syntax Extensions to RFC 3339

   The following rules extend the ABNF syntax defined in [RFC3339] in
   order to allow the inclusion of an optional suffix: the extended
   date/time format is described by the rule date-time-ext.

   time-zone-initial = ALPHA / "." / "_"
   time-zone-char    = time-zone-initial / DIGIT / "-" / "+"
   time-zone-part    = time-zone-initial *13(time-zone-char)
                       ; but not "." or ".."
   time-zone-name    = time-zone-part *("/" time-zone-part)
   time-zone         = "[" time-zone-name "]"

   namespace         = 1*alphanum
   namespace-key     = 1*alphanum
   suffix-key        = namespace ["-" namespace-key]

   suffix-value      = 1*alphanum
   suffix-values     = suffix-value *("-" suffix-value)
   suffix-tag        = "[" suffix-key "=" suffix-values "]"
   suffix            = [time-zone] *suffix-tag

   date-time-ext     = date-time suffix

   alphanum          = ALPHA / DIGIT

              Figure 2: ABNF grammar of extensions to RFC 3339

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3.5.  Examples

   Here are some examples of Internet extended date/time format.

   1996-12-19T16:39:57-08:00

             Figure 3: RFC 3339 date-time with timezone offset

   Figure 3 represents 39 minutes and 57 seconds after the 16th hour of
   December 19th, 1996 with an offset of -08:00 from UTC.  Note that
   this is the same instant in time as 1996-12-20T00:39:57Z, expressed
   in UTC.

   1996-12-19T16:39:57-08:00[America/Los_Angeles]

                      Figure 4: Adding a timezone name

   Figure 4 represents the exact same instant as the previous example
   but additionally specifies the human time zone associated with it
   ("Pacific Time") for time-zone-aware implementations to take into
   account.

   1996-12-19T16:39:57-08:00[America/Los_Angeles][u-ca=hebrew]

                Figure 5: Projecting to the Hebrew calendar

   Figure 5 represents the exact same instant but it informs calendar-
   aware implementations that they should project it to the Hebrew
   calendar.

   1996-12-19T16:39:57-08:00[x-foo=bar][x-baz=bat]

              Figure 6: Adding tags in private use namespaces

   Figure 6, based on Figure 3, utilizes the private use namespace to
   declare two additional pieces of information in the suffix that can
   be interpreted by any compatible implementations and ignored
   otherwise.

4.  IANA Considerations

   Multi-character namespaces are assigned by IANA using the "IETF
   Review" policy defined by [RFC8126]; the IETF review process needs to
   be based on the requirements laid out in Section 3.3.

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5.  Security Considerations

   TBD

6.  References

6.1.  Normative References

   [BCP47]    Phillips, A. and M. Davis, "Matching of Language Tags",
              BCP 47, RFC 4647, September 2006.

              Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
              Languages", BCP 47, RFC 5646, September 2009.

              <https://www.rfc-editor.org/info/bcp47>

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, DOI 10.17487/RFC2026, October 1996,
              <https://www.rfc-editor.org/info/rfc2026>.

   [RFC2028]  Hovey, R. and S. Bradner, "The Organizations Involved in
              the IETF Standards Process", BCP 11, RFC 2028,
              DOI 10.17487/RFC2028, October 1996,
              <https://www.rfc-editor.org/info/rfc2028>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/info/rfc3339>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

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6.2.  Informative References

   [CLDR]     "Unicode CLDR Project", <https://cldr.unicode.org>.

   [IERS]     "International Earth Rotation Service Bulletins",
              <https://www.iers.org/IERS/EN/Publications/Bulletins/
              bulletins.html>.

   [ISO8601]  International Organization for Standardization, "Data
              elements and interchange formats — Information interchange
              — Representation of dates and times", ISO 8601:1988, June
              1988, <https://www.iso.org/standard/15903.html>.

   [ITU-R-TF.460-6]
              "ITU-R TF.460-6. Standard-frequency and time-signal
              emissions", February 2002,
              <https://www.itu.int/rec/R-REC-TF.460/en>.

   [JAVAZDT]  "Java SE 8, java.time.format, DateTimeFormatter:
              ISO_ZONED_DATE_TIME",
              <https://docs.oracle.com/javase/8/docs/api/java/time/
              format/DateTimeFormatter.html#ISO_ZONED_DATE_TIME>.

   [RFC1305]  Mills, D., "Network Time Protocol (Version 3)
              Specification, Implementation and Analysis", RFC 1305,
              DOI 10.17487/RFC1305, March 1992,
              <https://www.rfc-editor.org/info/rfc1305>.

Appendix A.  Acknowledgements

   TBD

Authors' Addresses

   Ujjwal Sharma
   Igalia, S.L.
   Bugallal Marchesi, 22, 1º
   15008 A Coruña
   Spain

   Email: ryzokuken@igalia.com

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   Carsten Bormann
   Universität Bremen TZI
   Postfach 330440
   D-28359 Bremen
   Germany

   Phone: +49-421-218-63921
   Email: cabo@tzi.org

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