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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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 23 April 2022.
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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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