Telechat Review of draft-ietf-cbor-time-tag-10
review-ietf-cbor-time-tag-10-iotdir-telechat-wu-2023-10-17-00

This document is well written and defines CBOR tags for time duration and
period respectively. I feel these CBOR tags introduces rich semantics to
represent extended time format, which seems not suitable for resource
constraint IoT environment, please correct me if I am wrong. Here are a few
comments on the v-10: 1.Abstract One CBOR tag or three CBOR tags? It looks this
document defines and register 3 CBOR tags, why in this abstract say only one
CBOR tag is defined, together two CBOR tags? Does this mean that the other 2
CBOR tags are CBOR tags documented in some other specifications? 2.Introduction
The Same comment of the abstract is applied to the introduction, Why not say 3
CBOR tags are defined in this present document? 3.Section 1.1 mentions
including C++14's 0bnnn binary literals, Can you provide a reference for this?
4.Section 2 said: " Indication of timescale. Tags 0 and 1 are for UTC; however,
some interchanges are better performed on TAI. " Can tag 0 and tag 1 be applied
to TAI? For TAI, or only new CBOR tag should be applied to TAI? 5.Section 2
also said: " Intents might include information about time zones, daylight
savings times, preferred calendar representations, etc. " Has this additional
information such as time zones already been supported by 3 CBOR tags defined by
this document? Or leave this for future extension, e.g., extension defined in
section 3.7? Why leave this for future extension? Write another document for
these future extensions? 6.Section 2 said: " The present specification does not
take a position on whether tag 1 can be "fixed" to include, e.g., Decimal or
BigFloat representations.  It does define how to use these representations with
the extended time format. " Confused, does this mean that time format defined
in RFC8949 is not backward compatible with extended data format defined in this
document since tag 1 can not be fixed to support decimalfraction and bigfloat
while in this document key 4 and key 5 in extended data format can be used to
support decimalfraction and bigfloat。 7.Section 3 I am under impression that
the extended time format defined in this document choose to define different
CBOR tag, rather than extend from existing time related tags defined in
RFC8949, which seems to me , backward compatible to the time related tags
defined in RFC8949, I am wondering whether the extended time format defined in
this document is intended to replace time format defined in RFC 8949？ 8.Section
3 said: " Supplementary information may also be provided by additional unsigned
integer keys that are explicitly defined to provide supplementary information
("critical"; as these are required to be understood, there can be no confusion
with Base Time keys). Negative integer and text string keys always supply
supplementary information ("elective", and this will not be explicitly stated
below)." What is the difference between critical and elective? Not clear when I
have to choose to use critical, when I have to choose to use elective? In my
impression critical is related to unsigned integer while elective is related to
negative integer, so is there any use cases while only critical is allowed
while elective is forbidden? 9.Section 3 said: " Additional keys can be defined
by registering them in the Map Key Registry (Section 7.3).  Future keys may add:
   *  intent information such as timezone and daylight savings time,
      and/or possibly positioning coordinates, to express information
      that would indicate a local time."
I feel this paragraph is duplicated, which has already be described in section
2, paragraph 2. 10.In the formal definition of Tag 1001 in CDDL in section 3,
nint/text is used, what does nint in "nint/text" mean? uint or unsigned
integer? 11.Section 3.4 said: "If key -1 is not present, timescale value 0 is
implied." Does this mean timescale value 0 is default value? I also feel "value
0 is implied" is not formal language. 12.Section 3.5.4 said: "For this
document, uncertainty is defined as in Section 2.2.3 of [GUM]: "parameter,
associated with the result of a measurement, that characterizes the dispersion
of the values that could reasonably be attributed to the measurand".  More
specifically, the value for this key represents the extended uncertainty for k
= 2, in seconds. " What does measurand in this paragraph mean? Is K in “K=2”
Key 2? Can you provide reference for k=2? It is hard to understand without
context information. Can you provide a usage example for key = -7? 13.Section
3.6 Please clarify with an example on what key semantics difference between key
10 and key -10 14.Section 3.7 Section 3.6 and section 3.7 specify the rules for
key 10,-10, key 11,-11. Why allow key -10 and key 10 both present while not
allow key -11 and key 11 both present? Present in the same map or in two
different map? 15.Section 4 "In combination with an epoch identified in the
context, a duration can also be used to express an absolute time. " Can you
provide an example to use Duration as an absolute time? 16.Section 5 Is #6
representing CBOR major type 6? If yes, it seems not consistent with the text
in section 3 " An extended time is indicated by CBOR tag 1001, the content of
which is a map data item (CBOR major type 5)."