Support for iCalendar Relationships
draft-ietf-calext-ical-relations-11

[Ballot comment]
Thanks to Spencer Dawkins for his ARTART review.

There's a lot of missing punctuation in here, such as the prose in Sections 11.2 through 11.5, the end of the second and final paragraphs of 1.4, first paragraph of 2, "Property Parameters" of and the latter two examples in 8.2, etc.

This document needs a normative reference to ABNF (RFC 5234), and should mention explicitly that a lot of the ABNF tokens (e.g., "dur-value") are imported from RFC 5545.

[Ballot comment]
Thanks to Spencer Dawkins for his ARTART review.

There's a lot of missing punctuation in here, such as the prose in Sections 11.2 through 11.5, the end of the second and final paragraphs of 1.4, first paragraph of 2, "Property Parametes" of and the latter two examples in 8.2, etc.

This document needs a normative reference to ABNF (RFC 5234), and should mention explicitly that a lot of the ABNF tokens (e.g., "dur-value") are imported from RFC 5545.

[Ballot comment]
There's a lot of missing punctuation in here, such as the prose in Sections 11.2 through 11.5, the end of the second and final paragraphs of 1.4, first paragraph of 2, "Property Parametes" of and the latter two examples in 8.2, etc.

This document needs a normative reference to ABNF (RFC 5234), and should mention explicitly that a lot of the ABNF tokens (e.g., "dur-value") are imported from RFC 5545.

[Ballot comment]
Thank you to Catherine Meadows for the SECDIR review.

** Abstract.  The abstract text needs to mention that it is updating RFC5545.

** Section 6.2.  Typo. s/temporaly/temporarily/

** Section 8.1.  Per the example, “CONCEPT:http://example.com/event-types/arts/music” should this use https?

** Section 10.  Thanks for noting the RFC3986 considerations on using URIs.  Digging a bit more into the implementation approaches of the CONCEPT parameter, would clients be expected dereference the taxonomy URI in real-time?  I’m wondering if there would be a chance for tracking mechanism akin to a “web bug” on a web page or in HTML email.  For example, an .ics file is sent via an asynchronous mechanism (email) with a CONCEPT URI to something unique/unknown to the end-client and to a destination controlled by the sender or even a third party.  Could it function as a read-receipt or to harvest an identifier for the system the client is on (IP address)?

[Ballot discuss]
The ABNF for linkparam (§8.2) incorporates a "langparam" production, but
that is not defined in any of this document, RFC 5455, RFC 8288, or RFC
7986.  We need to define it somehow, whether by reference or directly.
RFC 5545 does define a LANGUAGE parameter (our prose references a "LANG"
parameter) and languageparam ABNF production, which is perhaps the
simplest explanation for what was intended.

[Ballot comment]
A couple broad comments before getting into the section-by-section
details:

I'm a little unclear on the value gained by having RELTYPE=REFID and
RELTYPE=CONCEPT.  If the semantics were just supposed to be "is a member
of the indicated group", then why do we need a relation type to say so.
But if there's some other semantics associated, where do we define those
semantics?

There are a number of places (e.g., §1.4) where this document uses the
term "collection" in a context that suggests that it should be a defined
term of iCalendar, corresponding roughly to a "site" or administrative
domain, but I didn't find any usage in RFC 5545 that would correspond to
what's being described here.  Can we say more about what level of grouping
this is intended to refer to?

Section 1.1

  The iCalendar [RFC5545] RELATED-TO property has no support for
  temporal relationships as used by standard project management tools.

I am admittedly not really the target audience of this specification, but
I have no idea what the "standard project management tools" are that are
being referred to.  Would (informative) references to a handful be
appropriate?

Section 1.2

  REFID is used to identify a key allowing the association of
  components that are related to the same object and retrieval of a
  component based on this key.  [...]

This says "related to the same *object*" (emphasis mine), but the rest of
the section just talks about an unstructured grouping.  It seems like we
could give some hint of the nature of the "object" to which all the
elements of the group are related, prior to the RELTYPE=REFID definition
in §5.

Section 1.3

  The current [RFC5545] CATEGORY property is used as a free form
  'tagging' field.  [...]

In light of the discussion in the previous section about grouping without
semantics, we might consider mentioning here that this is "tagging with
semantics", just vaguely defined ones, as opposed to the REFID-type
"tagging without semantics".

Section 1.4

  server-side management and stripping of inline data.  Clients may
  choose to handle attachments differently from the LINK property as
  they are often an integral part of the message - for example, the
  agenda.

(See the NITS entries as well, but) is it particularly noteworthy that
clients might handle LINKs different from ATTACHments?  They are different
properties after all -- why would someone assume equivalent treatment?

Section 1.5

  To facilitate offline display the link type may identify important
  pieces of data which should be downloaded in advance.

  In general, the calendar entity should be self explanatory without
  the need to download referenced meta-data such as a web page.

I'm not sure how to relate these two statements.  It sounds like a "
may happen, but in general don't do " scenario, in which case it might
flow better to give the general advice first, followed by the specific
scenario in which there is an exception to the general guidance.

Section 2

  The actual reference value can take three forms specified by the type
  parameter

Is this list fixed for eternity or do we want to give some guidance that
implementations need to prepare for future extensibility?

  REFERENCE:  In an XML environment it may be necessary to refer to a

This qualification in the description ("XML environment") suggests that
perhaps the name being used for these semantics is an overly generic name.

Section 4

We do have some text here about the GAP parameter that specifies the lead
or lag time here, but then we go on to describe the various RELTYPE values
in language like "cannot start until", "can only be completed after",
etc., that is very absolute and does not acknowledge the potential for a
GAP.  I think it would be helpful to reframe as that we are making a
comparison between the indicated pair of events, and that the relationship
between when the events occur is affected by the GAP interval.
(Also, the text in this section on the GAP parameter doesn't give a great
sense that the lead time would be a negative gap.)

Section 5

  RELTYPE=FIRST:  Indicates that the referenced calendar component is
      the first in a series the referenced calendar component is part
      of.

I wonder if we want to explicitly contrast this with PARENT and provide an
example of them being different.

Section 6.1

      In addition to the values defined here any value defined in
      [RFC8288] may be used.  However these uses SHOULD be documented in
      an RFC updating both [RFC5545] and [RFC8288]

In some sense this feels a little like saying "the current document SHOULD
have documented this stuff, but we didn't".  Is there anything useful to
say about why this documenting can't be done now?  (Oh, I guess there are
rather more values in the registry than I remembered, though the number of
them actually defined in RFC 8288 might be zero?)

Section 8.1

  Conformance:  This property can be specified zero or more times in
      any iCalendar component.
  [...]
      Within the "VEVENT", "VTODO", or "VJOURNAL" calendar components,
      more than one formal category can be specified by using multiple
      CONCEPT properties.

Are these two statements fully compatible?  The former seems to give
leeway to put multiple CONCEPT properties in any iCalendar component, but
the latter seems to limit to the "more than one" ability to just the three
named components.

Section 8.2

I am not entirely sure when the TEXT value type would be used.  If it's
just there to allow for certain types of extensibility, that might be
worth stating specifically.

      There is no mapping for [RFC8288] "title*", "anchor", "rev" or
      "media".

Maybe "there is currently no mapping"?  Or is the definition of such
mapping prevented for some technical reason(s)?

Section 9

  This specification updates the RELATED-TO property defined in
  Section 3.8.4.5 of [RFC5545].

I'd consider adding a note that "the contents of Section 9.1 below replace
Section 3.8.4.5 of [RFC5545]" to clarify the relationship between the two
sections.

Section 9.1

      By default, the property value points to another calendar
      component that has a PARENT relationship to the referencing
      object.  The "RELTYPE" property parameter is used to either
      explicitly state the default PARENT relationship type to the
      referenced calendar component or to override the default PARENT
      relationship type and specify either a CHILD or SIBLING
      relationship or a temporal relationship.

We allow some new relationship types that are neither CHILD/SIBLING nor
temporal (e.g., CONCEPT, REFID).  Should those get some text in the
description too?  (I am not sure if DEPENDS-ON and FIRST should get lumped
in as "temporal", either -- we don't do so in §5.)

      The FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH or STARTTOSTART
      relationships define temporal relationships as specified in the
      reltype parameter definition.

Likewise here, it seems some more discussion is in order for the other
relationship types.

      Changes to a calendar component referenced by this property can
      have an implicit impact on the related calendar component.  For

Do we want to say anything about changes to a component referenced by this
property using any of the new relationship types?

Section 10

Many thanks for referencing the URI security considerations and calling
out "reliability and consistency"!

We might say that the security considerations of RFC 5545 continue to
apply.

There are perhaps some privacy considerations if a user uses the new
CATEGORY or REFID functionality to expose information about a related
group of events, but it's a little hard to concoct a scenario where this
information gets to an attacker other than the calendar server, which is
already in something of a trusted position with respect to the user.

Are there any considerations about the new linking and relation operators
exposing information to other users about calendar components that they're
not authorized to access?

Very large "gap" parameters seem likely to lead to unexpected behavior.

NITS

Section 1.4

  iCalendar component.  This new LINK property is closely aligned to
  the LINK header defined in [RFC8288]

There are probably some pedantic distinctions that could be made here
relating to how RFC 8288 defines the generic concept of Web Linking (which
is not intrinsically tied to HTTP), as well as its expression in an HTTP
header *field*.

Also, please put a full stop at the end of the sentence.

  The ATTACH property defined in [RFC5545] is being extended to handle
  server-side management and stripping of inline data.  [...]

It's hard (at least on first read) to tell if this sentence is referring
to the RFC 8607 work or something being done by this document.

                                                        Clients may
  choose to handle attachments differently from the LINK property as
  they are often an integral part of the message - for example, the
  agenda.

Please clarify whether "they" refers to attachments of the LINK property.
The singular/plural signal implies it's "attachments" but we could
probably be more clear to the reader.

Also, two hyphens for an em dash.

Section 4

  This section defines the usual temporal relationships for use with

What's the context behind "usual"?  I don't remember (but may have missed)
a previous reference giving context for temporal relationships.

  RELTYPE=FINISHTOFINISH:  Task-B can only be completed after Task-A is
      finished.  The related tasks may run in parallel before
      completion.

      For example, if the goal is to prepare a meal, we start the
      potatoes, then the meat then the peas but they should all be
      cooked at the same time.

This doesn't look like a great example for "finish-to-finish", as we
prefer all things to finish at the same time, rather than with a strict
ordering between end times.

Section 6.1

  Registration:  These relation types are registered in [RFC8288]

I think we mean '''registered in the "Link Relation Types" registry
established by [RFC8288]'''.

Section 8.2

  Property Parameters:  The VALUE parameter is required.  Non-standard,
      reference type or format type parameters can also be specified on
      this property.  The LABEL parameter is defined in [RFC7986]

I'm not sure I see what in the ABNF would correspond to the "reference
type" parameters.  The closest seems to be the linkrelparam, but that's a
relation type, not a reference type.

Section 9.1

Looking at the diff from RFC 5545, we should title case "Property Name"
and "Value Type".  We also have changed the order in which we list the
options for property parameters but that seems unimportant.

Section 11.1

  The following iCalendar property names have been added to the
  iCalendar Properties Registry defined in Section 8.3.2 of [RFC5545]

Pedantically, RELATED-TO is not "added" but is rather covered by the "has
added a reference to this document where ... have been updated by this
document".  So if we were to keep this phrasing we might make two tables,
or we could try to fudge the wording here a bit.

[Ballot comment]
Thank you for the work put into this document. It appears to be useful especially if calendaring applications want to morph into project management style of calendaring.

Please find below some non-blocking COMMENT points (but replies would be appreciated even if only for my own education).

Special thanks to Bron Gondwana for the shepherd's write-up including the section about the WG consensus.

I hope that this helps to improve the document,

Regards,

-éric


https://www6.ietf.org/tools/idnits?url=https://www.ietf.org/archive/id/draft-ietf-calext-ical-relations-09.txt flags multiple errors and warnings. All of them look easy to address.

I also support Erik Kline's comment about the use of "https" everywhere.


## Section 4

It would be nice to add some explanations around the direction of the arrow.

Figure 2, I like the example, but the graphic has 2 elements while the example text has 3.

# Section 6.2

Even if obvious, "dur-value" is not described in the text of this section.

May I also assume that CALEXT has duration types ? So, that there is no need to describe the syntex of this value ?

[Ballot comment]
[S2; nit]

* "it's use" -> "its use", I think

[S8.1, S8.2, S9.1; nit]

* Is "http" important to the examples, or should/could these be "https"?

(Via drafts-lastcall@iana.org): IESG/Authors/WG Chairs:

The IANA Functions Operator has completed its review of draft-ietf-calext-ical-relations-08. If any part of this review is inaccurate, please let us know.

The IANA Functions Operator has a question about one of the actions requested in the IANA Considerations section of this document.

The IANA Functions Operator understands that, upon approval of this document, there are six actions which we must complete.

First, in the Properties registry on the iCalendar Element Registries page located at:

https://www.iana.org/assignments/icalendar/

Three new registrations are to be made as follows:

Property: CONCEPT
Status: Current
Reference: [ RFC-to-be; Section 8.1 ]

Property: LINK
Status: Current
Reference: [ RFC-to-be; Section 8.2 ]

Property: REFID
Status: Current
Reference: [ RFC-to-be; Section 8.3 ]

As this document requests registrations in an Expert Review (see RFC 8126) registry, we will initiate the required Expert Review via a separate request. This review must be completed before the document's IANA state can be changed to "IANA OK."

Second, also in the Properties registry on the iCalendar Element Registries page located at:

https://www.iana.org/assignments/icalendar/

the existing registration for

Property: RELATED-TO

will have its reference updated by the addition of [ RFC-to-be; Section 9 ]

Third, in the Parameters registry also on the iCalendar Element Registries page located at:

https://www.iana.org/assignments/icalendar/

two new registrations will be made as follows:

Parameter: GAP
Status: Current
Reference: [ RFC-to-be; Section 6.2 ]

Parameter: REL
Status: Current
Reference: [ RFC-to-be; Section 6.1 ]

As this also requests registrations in an Expert Review (see RFC 8126) registry, we will initiate the required Expert Review via a separate request. This review must be completed before the document's IANA state can be changed to "IANA OK."

Fourth, in the Value Data Types registry also on the iCalendar Element Registries page located at:

https://www.iana.org/assignments/icalendar/

two new registrations will be made as follows:

Value Data Type: REFERENCE
Status: Current
Reference: [ RFC-to-be; Section 7 ]

Value Data Type: UID
Status: Current
Reference: [ RFC-to-be; Section 7 ]

As this also requests registrations in an Expert Review (see RFC 8126) registry, we will initiate the required Expert Review via a separate request. This review must be completed before the document's IANA state can be changed to "IANA OK."

Fifth, in the Relationship Types registry also on the iCalendar Element Registries page located at:

https://www.iana.org/assignments/icalendar/

eight new registrations will be made as follows:

Relationship Type: CONCEPT
Status: Current
Reference: [ RFC-to-be; Section 5 ]

Relationship Type: DEPENDS-ON
Status: Current
Reference: [ RFC-to-be; Section 5 ]

Relationship Type: FINISHTOFINISH
Status: Current
Reference: [ RFC-to-be; Section 4 ]

Relationship Type: FINISHTOSTART
Status: Current
Reference: [ RFC-to-be; Section 4 ]

Relationship Type: FIRST
Status: Current
Reference: [ RFC-to-be; Section 5 ]

Relationship Type: REFID
Status: Current
Reference: [ RFC-to-be; Section 5 ]

Relationship Type: STARTTOFINISH
Status: Current
Reference: [ RFC-to-be; Section 4 ]

Relationship Type: STARTTOSTART
Status: Current
Reference: [ RFC-to-be; Section 4 ]

As this also requests registrations in an Expert Review (see RFC 8126) registry, we will initiate the required Expert Review via a separate request. This review must be completed before the document's IANA state can be changed to "IANA OK."

Sixth, section 11.5 of the current document requests:

"The following link relation values have been added to the Reference Types Registry defined in Section 6.2.2 of [RFC8288]"

IANA Question --> is this request correct? RFC8288 does not have a section 6.2.2. In addition, the link relation types registry established by RFC8288 requires a relation name and description.

Relation Name:
Description:
Reference: [ RFC-to-be ]

The IANA Functions Operator understands that these are the only actions required to be completed upon approval of this document.

Note: The actions requested in this document will not be completed until the document has been approved for publication as an RFC. This message is meant only to confirm the list of actions that will be performed.

Thank you,

Sabrina Tanamal
Lead IANA Services Specialist

The following Last Call announcement was sent out (ends 2021-10-28):

From: The IESG
To: IETF-Announce
CC: Bron Gondwana , brong@fastmailteam.com, calext-chairs@ietf.org, calsify@ietf.org, draft-ietf-calext-ical-relations@ietf.org, francesca.palombini@ericsson.com
Reply-To: last-call@ietf.org
Sender:
Subject: Last Call:  (Support for iCalendar Relationships) to Proposed Standard


The IESG has received a request from the Calendaring Extensions WG (calext)
to consider the following document: - 'Support for iCalendar Relationships'
  as Proposed Standard

The IESG plans to make a decision in the next few weeks, and solicits final
comments on this action. Please send substantive comments to the
last-call@ietf.org mailing lists by 2021-10-28. Exceptionally, comments may
be sent to iesg@ietf.org instead. In either case, please retain the beginning
of the Subject line to allow automated sorting.

Abstract


  This specification updates RELATED-TO defined in iCalendar (RFC5545)
  and introduces new iCalendar properties LINK, CONCEPT and REFID to
  allow better linking and grouping of iCalendar components and related
  data.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-calext-ical-relations/



No IPR declarations have been submitted directly on this I-D.

Document Shepherd Write-Up for draft-ietf-calext-ical-relations

1. This document is being requested as an Proposed Standard because it
extends an existing Proposed Standard (RFC5545).

The request type is indicated in the title page header as "Standards Track".

2.

Technical Summary

  This spec extends the iCalendar format (RFC5545) to add new
  properties (LINK, CONCEPT and REFID) to allow better linking
  and grouping of related iCalendar records.

Working Group Summary

  This document has been around for a long time and been through
  multiple revisions and discussions since it was first proposed
  in 2013, and first accepted by this working group in 2016.

  The main delay has been my (Bron, document Shepherd) fault, as
  it's had multiple working group last calls, and then I've just
  not gotten around to submitting it until the document expired.
  Blame 2020.

Document Quality

  The extensions to iCalendar are all very easy to understand and
  to implement.  The concepts in this document have already been
  implemented in the jscalendar format (RFC8984) - though there is
  not need to cross-reference them, as that will be done in a
  separate mapping document between the two protocols, which is
  still being finalised, and will reference both this docuement
  and that one (draft-ietf-calext-jscalendar-icalendar).

Personnel

  Document Shepherd - Bron Gondwana (CALEXT co-chair)
  Responsible Area Director - Francesca Palombini


3. The Document Shepherd has read the document through in detail.

4. There are no concerns about reviews, this document has been well reviewed.

5. There is no review required for the document by other areas.

6. There are no concerns with this document that IESG should be aware of.

7. Yes, the author has been contacted and confirmed and confirmed that
they have no disclosures.

8. There have been no IPR disclosures filed.

9. The WG consensus is solid.

10. There has been no discontent.

11. idnits notices a missing reference to RFC3986, which appears to
be a tooling bug and easily resolved in the editing process.

12. This document doesn't define anything which needs formal review
outside the working group.

13. All references have been identified as normative.

14. All normative references are published standards at the IETF or W3C.

15. There is a downref to an informational RFC, RFC8607.  Per that RFC:

  Although this extension to CalDAV has wide deployment, its design does
  not comply with some of the best current practices of HTTP. Rather
  than creating interoperability problems with deployed code, it was
  decided to simply document how existing implementations interoperate.

  So this reference is required to specify how this extension will also
  interact with the deployed base of managed attachments.

16. This RFC does not change the status of any other RFC.

17. The IANA considerations ask for entries to be added 5 separate
icalendar registries.  The registrations are formatted as tables and
clearly specify the values for all the fields in each registry.
The author of this specification is one of the expert reviewers for
these registries.

18. There are no new registries created.

19. The ABNF section is spread through the document, and was validated with
Chris Newman's tool.

Document Shepherd Write-Up for draft-ietf-calext-ical-relations

1. This document is being requested as an Proposed Standard because it
extends an existing Proposed Standard (RFC5545).

The request type is indicated in the title page header as "Standards Track".

2.

Technical Summary

  This spec extends the iCalendar format (RFC5545) to add new
  properties (LINK, CONCEPT and REFID) to allow better linking
  and grouping of related iCalendar records.

Working Group Summary

  This document has been around for a long time and been through
  multiple revisions and discussions since it was first proposed
  in 2013, and first accepted by this working group in 2016.

  The main delay has been my (Bron, document Shepherd) fault, as
  it's had multiple working group last calls, and then I've just
  not gotten around to submitting it until the document expired.
  Blame 2020.

Document Quality

  The extensions to iCalendar are all very easy to understand and
  to implement.  The concepts in this document have already been
  implemented in the jscalendar format (RFC8984) - though there is
  not need to cross-reference them, as that will be done in a
  separate mapping document between the two protocols, which is
  still being finalised, and will reference both this docuement
  and that one (draft-ietf-calext-jscalendar-icalendar).

Personnel

  Document Shepherd - Bron Gondwana (CALEXT co-chair)
  Responsible Area Director - Francesca Palombini


3. The Document Shepherd has read the document through in detail.

4. There are no concerns about reviews, this document has been well reviewed.

5. There is no review required for the document by other areas.

6. There are no concerns with this document that IESG should be aware of.

7. Yes, the author has been contacted and confirmed and confirmed that
they have no disclosures.

8. There have been no IPR disclosures filed.

9. The WG consensus is solid.

10. There has been no discontent.

11. idnits notices a missing reference to RFC3986, which appears to
be a tooling bug and easily resolved in the editing process.

12. This document doesn't define anything which needs formal review
outside the working group.

13. All references have been identified as normative.

14. All normative references are published standards at the IETF or W3C.

15. There is a downref to an informational RFC, RFC8607.  Per that RFC:

  Although this extension to CalDAV has wide deployment, its design does
  not comply with some of the best current practices of HTTP. Rather
  than creating interoperability problems with deployed code, it was
  decided to simply document how existing implementations interoperate.

  So this reference is required to specify how this extension will also
  interact with the deployed base of managed attachments.

16. This RFC does not change the status of any other RFC.

17. The IANA considerations ask for entries to be added 5 separate
icalendar registries.  The registrations are formatted as tables and
clearly specify the values for all the fields in each registry.
The author of this specification is one of the expert reviewers for
these registries.

18. There are no new registries created.

19. The ABNF section is spread through the document, and was validated with
Chris Newman's tool.