Internet-Draft Event Publishing Extensions to iCalendar March 2021
Douglass Expires 27 September 2021 [Page]
Workgroup:
Network Working Group
Internet-Draft:
draft-ietf-calext-eventpub-extensions-19
Updates:
5545 (if approved)
Published:
Intended Status:
Standards Track
Expires:
Author:
M. Douglass
Bedework

Event Publishing Extensions to iCalendar

Abstract

This specification updates RFC5545 by introducing a number of new iCalendar properties and components which are of particular use for event publishers and in social networking.

This specification also defines a new STRUCTURED-DATA property for iCalendar RFC5545 to allow for data that is directly pertinent to an event or task to be included with the calendar data.

Status of This Memo

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

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 27 September 2021.

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Table of Contents

1. Introduction

The currently existing iCalendar standard [RFC5545] lacks useful methods for referencing additional, external information relating to calendar components. Additionally there is no standard way to provide rich text descriptions or meta-data associated with the event.

Current practice is to embed this information as links in the description or to add non-standard properties as defined in [RFC5545] section 3.8.8.2.

This document updates [RFC5545] to define a number of properties and components referencing such external information that can provide additional information about an iCalendar component. The intent is to allow interchange of such information between applications or systems (e.g., between clients, between client and server, and between servers). Formats such as vCard [RFC2426] are likely to be most useful to the receivers of such events as they may be used in other applications - such as address books.

1.1. Conventions Used in This Document

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.

1.2. Terms Used in This Document

Event:
When the (perhaps with a capitalised 'E') word 'event' is used we are referring to gatherings, formal or informal. For example a sports event, a party or a concert.
Social Calendaring:
Historically, calendar data and scheduling has been heavily biased towards meetings in a corporate environment. Some of the features defined in this document are to support a more informal, i.e. social, model. For example, we may want to record who is participating in a public event.

2. Components and properties

Previous extensions to the calendaring standards have been largely restricted to the addition of properties or parameters. This is partly because iCalendar libraries had trouble handling components nested deeper than those defined in [RFC5545].

In a break with this 'tradition' this specification defines a number of components rather than properties. This is a better match for the way [W3C.REC-xml-20081126] and JSON [RFC8259] handle such structures and allows richer definitions.

It also allows for the addition of extra properties inside the components and resolves some of the problems of trying to add detailed information as a parameter.

3. Typed References

The properties and components defined here can all reference external meta-data which may be used by applications to provide further information to users. By providing type information, clients and servers are able to discover interesting references and make use of them, perhaps for indexing or the presenting of additional related information for the user.

As always, clients should exercise caution in following references to external data.

The [RFC5545] LOCATION property provides only an unstructured single text value for specifying the location where an event (or task) will occur. This is inadequate for use cases where structured location information (e.g. address, region, country, postal code) is required or preferred, and limits widespread adoption of iCalendar in those settings.

Using the VLOCATION component, rich information about multiple locations can be communicated in a STRUCTURED-DATA property, for example, address, region, country, postal code as well as other information such as parking availability, nearby restaurants and the venue. Servers and clients can retrieve the objects when storing the event and use them to index by geographic location.

When a calendar client receives a calendar component it can search the set of locations looking for those of particular interest. The LOCATION-TYPE property and STRUCTURED-DATA FMTTYPE parameter, if supplied, can be used to help the selection.

The PARTICIPANT component is designed to handle common use cases in event publication. It is generally important to provide information about the organizers of such events. Sponsors wish to be referenced in a prominent manner. In social calendaring it is often important to identify the active participants in the event, for example a school sports team, and the inactive participants, for example the parents.

The PARTICIPANT component can be used to provide useful extra data about an attendee. For example a location inside the PARTICIPANT gives the actual location of a remote attendee. (But see the note about privacy.)

Alternatively the PARTICIPANT component can be used to provide a reference - perhaps the address for mailing lists.

3.1. Use Cases

The main motivation for these changes has been event publication but there are opportunities for use elsewhere. The following use cases will describe some possible scenarios.

3.1.1. Piano Concert Performance

In putting together a concert there are many participants: piano tuner, performer, stage hands etc. In addition there are sponsors and various contacts to be provided. There will also be a number of related locations. A number of events can be created, all of which relate to the performance in different ways.

There may be an iTIP [RFC5546] meeting request for the piano tuner who will arrive before the performance. Other members of staff may also receive meeting requests.

An event can also be created for publication which will have a PARTICIPANT component for the pianist providing a reference to vCard [RFC2426] information about the performer. This event would also hold information about parking, local subway stations and the venue itself. In addition, there may be sponsorship information for sponsors of the event and perhaps paid sponsorship properties essentially advertising local establishments.

3.1.2. Itineraries

These additions also provide opportunities for the travel industry. When booking a flight the PARTICIPANT component can be used to provide references to businesses at the airports and to car hire businesses at the destination.

The embedded location information can guide the traveler at the airport or to their final destination. The contact information can provide detailed information about the booking agent, the airlines, car hire companies and the hotel.

3.1.2.1. Reserving facilities

For a meeting, the size of a room and the equipment needed depends to some extent on the number of attendees actually in the room.

A meeting may have many attendees none of which are co-located. The current ATTENDEE property does not allow for the addition of such meta-data. The PARTICIPANT component allows attendees to specify their location.

4. Modifications to Calendar Components

The following changes to the syntax defined in iCalendar [RFC5545] are made here. New elements are defined in subsequent sections.

   ; Addition of PARTICIPANT, VLOCATION and VRESOURCE
   ; as valid components
   eventc     = "BEGIN" ":" "VEVENT" CRLF
                eventprop *alarmc *participantc *locationc *resourcec
                "END" ":" "VEVENT" CRLF

   ; Addition of properties STYLED-DESCRIPTION and STRUCTURED-DATA
   eventprop  =/ *styleddescription
                 *sdataprop

   ; Addition of PARTICIPANT, VLOCATION and VRESOURCE
   ; as valid components
   todoc      = "BEGIN" ":" "VTODO" CRLF
                todoprop *alarmc *participantc *locationc *resourcec
                "END" ":" "VTODO" CRLF

   ; Addition of properties STYLED-DESCRIPTION, STRUCTURED-DATA
   todoprop =/ *styleddescription
               *sdataprop

   ; Addition of PARTICIPANT, VLOCATION and VRESOURCE
   ; as valid components
   journalc   = "BEGIN" ":" "VJOURNAL" CRLF
                jourprop *participantc *locationc *resourcec
                "END" ":" "VJOURNAL" CRLF

   ; Addition of properties STYLED-DESCRIPTION, STRUCTURED-DATA
   jourprop =/ *styleddescription
               *sdataprop

   ; Addition of PARTICIPANT, VLOCATION and VRESOURCE
   ; as valid components
   freebusyc  = "BEGIN" ":" "VFREEBUSY" CRLF
                fbprop *participantc *locationc *resourcec
                "END" ":" "VFREEBUSY" CRLF

   ; Addition of property STYLED-DESCRIPTION
   fbprop     =/ *styleddescription

5. New Property Parameters

5.1. Order

Parameter name:
ORDER
Purpose:
To define ordering for the associated property.
Format Definition:

This parameter is defined by the following notation:

  orderparam    = "ORDER" "=" integer
                  ;           Must be greater than or equal to 1
Description:
The ORDER parameter is OPTIONAL and is used to indicate the relative ordering of the corresponding instance of a property. Its value MUST be an integer greater than or equal to 1 that specifies the order with 1 being the first in the ordering.
When the parameter is absent, the default MUST be to interpret the property instance as being ordered last, that is, the property will appear after any other instances of the same property with any value of ORDER.
When any ORDER parameters have the same value all the associated properties appear as a group within which there is no defined order.
Note that the value of this parameter is to be interpreted only in relation to values assigned to other corresponding instances of the same property in the same entity.
This parameter MUST NOT be applied to a property that does not allow multiple instances.
Example uses:
The ORDER may be applied to the PARTICIPANT-TYPE property to indicate the relative importance of the participant, for example as a sponsor or a performer. For example, ORDER=1 could define the principal performer or soloist.

5.2. Schema

Parameter Name:
SCHEMA
Purpose:
To specify the schema used for the content of a "STRUCTURED-DATA" property value.
Format Definition:

This parameter is defined by the following notation:

  schemaparam    = "SCHEMA" "=" DQUOTE uri DQUOTE
Description:
This property parameter SHOULD be specified on "STRUCTURED-DATA" properties. When present it provides identifying information about the nature of the content of the corresponding "STRUCTURED-DATA" property value. This can be used to supplement the media type information provided by the "FMTTYPE" parameter on the corresponding property.
Example:
  STRUCTURED-DATA;FMTTYPE=application/ld+json;
   SCHEMA="https://schema.org/FlightReservation";
   ENCODING=BASE64;VALUE=BINARY:ICAgIDxzY3JpcHQgdHlwZT0iYXBwb
   GljYXRpb24vbGQranNvbiI+CiAgICB7CiAgICAgICJAY29
   udGV4dCI6ICJodHRwOi8vc2NoZW1hLm9yZyIsCiAgICAgICJAdHlwZSI
   6ICJGbGlnaHRSZXNlcnZhdGlvbiIsCiAgICAgICJyZXNlcnZhdGlvbkl
   kIjogIlJYSjM0UCIsCiAgICAgICJyZXNlcnZhdGlvblN0YXR1cyI6ICJ
   odHRwOi8vc2NoZW1hLm9yZy9SZXNlcnZhdGlvbkNvbmZpcm1lZCIsCiA
   gICAgICJwYXNzZW5nZXJQcmlvcml0eVN0YXR1cyI6ICJGYXN0IFRyYWN
   rIiwKICAgICAgInBhc3NlbmdlclNlcXVlbmNlTnVtYmVyIjogIkFCQzE
   yMyIsCiAgICAgICJzZWN1cml0eVNjcmVlbmluZyI6ICJUU0EgUHJlQ2h
   lY2siLAogICAgICAidW5kZXJOYW1lIjogewogICAgICAgICJAdHlwZSI
   6ICJQZXJzb24iLAogICAgICAgICJuYW1lIjogIkV2YSBHcmVlbiIKICA
   gICAgfSwKICAgICAgInJlc2VydmF0aW9uRm9yIjogewogICAgICAgICJ
   AdHlwZSI6ICJGbGlnaHQiLAogICAgICAgICJmbGlnaHROdW1iZXIiOiA
   iVUExMTAiLAogICAgICAgICJwcm92aWRlciI6IHsKICAgICAgICAgICJ
   AdHlwZSI6ICJBaXJsaW5lIiwKICAgICAgICAgICJuYW1lIjogIkNvbnR
   pbmVudGFsIiwKICAgICAgICAgICJpYXRhQ29kZSI6ICJDTyIsCiAgICA
   gICAgICAiYm9hcmRpbmdQb2xpY3kiOiAiaHR0cDovL3NjaGVtYS5vcmc
   vWm9uZUJvYXJkaW5nUG9saWN5IgogICAgICAgIH0sCiAgICAgICAgInN
   lbGxlciI6IHsKICAgICAgICAgICJAdHlwZSI6ICJBaXJsaW5lIiwKICA
   gICAgICAgICJuYW1lIjogIlVuaXRlZCIsCiAgICAgICAgICAiaWF0YUN
   vZGUiOiAiVUEiCiAgICAgICAgfSwKICAgICAgICAiZGVwYXJ0dXJlQWl
   ycG9ydCI6IHsKICAgICAgICAgICJAdHlwZSI6ICJBaXJwb3J0IiwKICA
   gICAgICAgICJuYW1lIjogIlNhbiBGcmFuY2lzY28gQWlycG9ydCIsCiA
   gICAgICAgICAiaWF0YUNvZGUiOiAiU0ZPIgogICAgICAgIH0sCiAgICA
   gICAgImRlcGFydHVyZVRpbWUiOiAiMjAxNy0wMy0wNFQyMDoxNTowMC0
   wODowMCIsCiAgICAgICAgImFycml2YWxBaXJwb3J0IjogewogICAgICA
   gICAgIkB0eXBlIjogIkFpcnBvcnQiLAogICAgICAgICAgIm5hbWUiOiA
   iSm9obiBGLiBLZW5uZWR5IEludGVybmF0aW9uYWwgQWlycG9ydCIsCiA
   gICAgICAgICAiaWF0YUNvZGUiOiAiSkZLIgogICAgICAgIH0sCiAgICA
   gICAgImFycml2YWxUaW1lIjogIjIwMTctMDMtMDVUMDY6MzA6MDAtMDU
   6MDAiCiAgICAgIH0KICAgIH0KICAgIDwvc2NyaXB0Pg==

5.3. Derived

Parameter Name:
DERIVED
Purpose:
To specify that the value of the associated property is derived from some other property value or values.
Format Definition:

This parameter is defined by the following notation:

  derivedparam    = "DERIVED" "=" ("TRUE" / "FALSE")
  ; Default is FALSE
Description:
This property parameter MAY be specified on any property when the value is derived from some other property or properties. When present with a value of TRUE clients MUST NOT update the property.
As an example, if a STYLED-DESCRIPTION property is present with FMTTYPE="application/rtf" then there may be an additional STYLED-DESCRIPTION property with FMTTYPE="text/html" and DERIVED=TRUE and a value created from the rtf value.
Example:
  STYLED-DESCRIPTION;FMTTYPE=text/html;
   DERIVED=TRUE:<html>...</html>

6. New Properties

This specification makes use of the NAME property which is defined in [RFC7986]

6.1. Location Type

Property name:
LOCATION-TYPE
Purpose:
To specify the type(s) of a location.
Value type:
The value type for this property is TEXT. The allowable values are defined below.
Description:
This property MAY be specified in VLOCATION components and provides a way to differentiate multiple locations. For example, it allows event producers to provide location information for the venue and the parking.
Format Definition:

This property is defined by the following notation:

   loctype      = "LOCATION-TYPE" loctypeparam ":"
                  text *("," text)
                  CRLF

   loctypeparam   = *(";" other-param)
Multiple values may be used if the location has multiple purposes, for example a hotel and a restaurant.
Values for this parameter are taken from the values defined in [RFC4589] section 3. New location types SHOULD be registered in the manner laid down in section 5 of that specification.

6.2. Participant Type

Property name:
PARTICIPANT-TYPE
Purpose:
To specify the type of participant.
Value type:
The value type for this property is TEXT. The allowable values are defined below.
Property Parameters:
Non-standard parameters can be specified on this property.
Conformance:
This property MUST be specified once within a PARTICIPANT component.
Description:
This property defines the type of participation in events or tasks. Participants can be individuals or organizations, for example a soccer team, the spectators, or the musicians.
Format Definition:

This property is defined by the following notation:

  participanttype   = "PARTICIPANT-TYPE" partvalueparam ":"
                       partvalue CRLF

  partvalue    = ("ACTIVE"
                 / "INACTIVE"
                 / "SPONSOR"
                 / "CONTACT"
                 / "BOOKING-CONTACT"
                 / "EMERGENCY-CONTACT"
                 / "PUBLICITY-CONTACT"
                 / "PLANNER-CONTACT"
                 / "PERFORMER"
                 / "SPEAKER"
                 / iana-token)     ; Other IANA-registered
                                   ; values

  partvalueparam   = *(";" other-param)
Example:

The following is an example of this property:

   PARTICIPANT-TYPE:SPEAKER

The registered values for the PARTICIPANT-TYPE property have the meanings described here:

ACTIVE:
A participant taking an active role - for example a team member.
INACTIVE:
A participant taking an inactive role - for example an audience member.
SPONSOR:
A sponsor of the event. The ORDER parameter may be used with this participant type to define the relative order of multiple sponsors.
CONTACT:
Contact information for the event. The ORDER parameter may be used with this participant type to define the relative order of multiple contacts.
BOOKING-CONTACT:
Contact information for reservations or payment
EMERGENCY-CONTACT:
Contact in case of emergency
PUBLICITY-CONTACT:
Contact for publicity
PLANNER-CONTACT:
Contact for the event planner or organizer
PERFORMER:
A performer - for example the soloist or the accompanist. The ORDER parameter may be used with this participant type to define the relative order of multiple performers. For example, ORDER=1 could define the principal performer or soloist.
SPEAKER:
Speaker at an event

6.3. Resource Type

Property name:
RESOURCE-TYPE
Purpose:
To specify the type of resource.
Value type:
The value type for this property is TEXT. The allowable values are defined below.
Format Definition:

This property is defined by the following notation:

   restypeprop   = "RESOURCE-TYPE" restypeparam ":"
                   restypevalue CRLF

   restypevalue  = ("ROOM"
                  / "PROJECTOR"
                  / "REMOTE-CONFERENCE-AUDIO"
                  / "REMOTE-CONFERENCE-VIDEO"
                  / iana-token)     ; Other IANA-registered
                  ; values

   restypeparam   = *(";" other-param)
Description:
This property MAY be specified in VRESOURCE components and provides a way to differentiate multiple resources.
The registered values are described below. New resource types SHOULD be registered in the manner laid down in this specification.
ROOM:
A room for the event/meeting.
PROJECTOR:
Projection equipment.
REMOTE-CONFERENCE-AUDIO:
Audio remote conferencing facilities.
REMOTE-CONFERENCE-VIDEO:
Video remote conferencing facilities.

6.4. Calendar Address

Property name:
CALENDAR-ADDRESS
Purpose:
To specify the calendar address for a participant.
Value type:
CAL-ADDRESS
Property Parameters:
IANA-registered, or non-standard property parameters can be specified on this property.
Conformance:
This property MAY be specified once within a PARTICIPANT component.
Description:
This property provides a calendar user address for the participant. If there is an ATTENDEE property with the same value then the participant is schedulable.
Format Definition:

This property is defined by the following notation:

   calendaraddress   = "CALENDAR-ADDRESS" caladdressparam ":"
                  cal-address CRLF

    caladdressparam   = *(";" other-param)

6.5. Styled-Description

Property name:
STYLED-DESCRIPTION
Purpose:
This property provides for one or more rich-text descriptions to replace that provided by the DESCRIPTION property.
Value type:
There is no default value type for this property. The value type can be set to URI or TEXT. Other text-based value types can be used when defined in the future. Clients MUST ignore any properties with value types they do not understand.
Property Parameters:
IANA-registered, non-standard, id, alternate text representation, format type, derived and language property parameters can be specified on this property.
Conformance:
The property can be specified multiple times in the "VEVENT", "VTODO", "VJOURNAL", "VFREEBUSY", "PARTICIPANT", or "VALARM" calendar components.
If it does appear more than once there MUST be exactly one instance of the property with no DERIVED parameter or DERIVED=FALSE. All others MUST have DERIVED=TRUE.
Additionally, if there is one or more STYLED-DESCRIPTION property then the DESCRIPTION property should be either absent or have the parameter DERIVED=TRUE.
Description:
This property supports rich-text descriptions, for example HTML. Event publishers typically wish to provide more and better formatted information about the event.
This property is used in the "VEVENT" and "VTODO" to capture lengthy textual descriptions associated with the activity. This property is used in the "VJOURNAL" calendar component to capture one or more textual journal entries. This property is used in the "VALARM" calendar component to capture the display text for a DISPLAY category of alarm, and to capture the body text for an EMAIL category of alarm. In the PARTICIPANT component it provides a detailed description of the participant.
VALUE=TEXT is used to provide rich-text inline as the property value.
VALUE=URI is used to provide a link to rich-text content which is expected to be displayed inline as part of the event.
In either case the DESCRIPTION property should be absent or contain a plain text rendering of the styled text.
Applications MAY attempt to guess the media type of the resource via inspection of its content if and only if the media type of the resource is not given by the "FMTTYPE" parameter. If the media type remains unknown, calendar applications SHOULD treat it as type "text/html" and process the content as defined in [W3C.REC-html51-20171003]
Multiple STYLED-DESCRIPTION properties may be used to provide different formats or different language variants. However all but one MUST have DERIVED=TRUE.
Format Definition:

This property is defined by the following notation:

  styleddescription = "STYLED-DESCRIPTION" styleddescparam ":"
                     styleddescval CRLF

  styleddescparam   = *(
                     ; The following is REQUIRED,
                     ; but MUST NOT occur more than once.
                     ;
                     (";" "VALUE" "=" ("URI" / "TEXT")) /
                     ;
                     ; The following are OPTIONAL,
                     ; but MUST NOT occur more than once.
                     ;
                     (";" altrepparam) / (";" languageparam) /
                     (";" fmttypeparam) / (";" derivedparam) /
                     ;
                     ; the following is OPTIONAL
                     ; and MAY occur more than once
                     ;
                     (";" other-param)
                     )

  styleddescval   = ( uri / text )
  ;Value MUST match value type
Example:

The following is an example of this property. It points to an html description.

       STYLED-DESCRIPTION;VALUE=URI:http://example.org/desc001.html

6.6. Structured-Data

Property Name:
STRUCTURED-DATA
Purpose:
This property specifies ancillary data associated with the calendar component.
Value Type:
There is no default value type for this property. The value type can be set to TEXT, BINARY or URI
Property Parameters:
IANA-registered, non-standard, inline encoding and value data type property parameters can be specified on this property. The format type and schema parameters can be specified on this property and MUST be present for text or inline binary encoded content information.
Conformance:
This property can be specified multiple times in an iCalendar object. Typically it would be used in "VEVENT", "VTODO" or "VJOURNAL" calendar components.
Description:
The existing properties in iCalendar cover key elements of events and tasks such as start time, end time, location, summary, etc. However, different types of events often have other specific "fields" that it is useful to include in the calendar data. For example, an event representing an airline flight could include the airline, flight number, departure and arrival airport codes, check-in and gate-closing times etc. As another example, a sporting event might contain information about the type of sport, the home and away teams, the league the teams are in, information about nearby parking, etc.
This property is used to specify ancillary data in some structured format either directly (inline) as a "TEXT" or "BINARY" value or as a link via a "URI" value.
Rather than define new iCalendar properties for the variety of event types that might occur, it would be better to leverage existing schemas for such data. For example, schemas available at https://schema.org include different event types. By using standard schemas, interoperability can be improved between calendar clients and non-calendaring systems that wish to generate or process the data.
This property allows the direct inclusion of ancillary data whose schema is defined elsewhere. This property also includes parameters to clearly identify the type of the schema being used so that clients can quickly and easily spot what is relevant within the calendar data and present that to users or process it within the calendaring system.
iCalendar does support an "ATTACH" property which can be used to include documents or links to documents within the calendar data. However, that property does not allow data to be included as a "TEXT" value (a feature that "STRUCTURED-DATA" does allow), plus attachments are often treated as "opaque" data to be processed by some other system rather than the calendar client. Thus the existing "ATTACH" property is not sufficient to cover the specific needs of inclusion of schema data. Extending the "ATTACH" property to support a new value type would likely cause interoperability problems. Additionally some implementations manage attachments by stripping them out and replacing with a link to the resource. Thus a new property to support inclusion of schema data is warranted.
Format Definition:

This property is defined by the following notation:

   sdataprop    = "STRUCTURED-DATA" sdataparam
                    (
                      ";" "VALUE" "=" "TEXT"
                      ":" text
                    ) /
                    (
                      ";" "ENCODING" "=" "BASE64"
                      ";" "VALUE" "=" "BINARY"
                      ":" binary
                    ) /
                    (
                      ";" "VALUE" "=" "URI"
                      ":" uri
                    )
                    CRLF

  sdataparam  = *(
                   ;
                   ; The following is OPTIONAL for a URI value,
                   ; REQUIRED for a TEXT or BINARY value,
                   ; and MUST NOT occur more than once.
                   ;
                   (";" fmttypeparam) /
                   (";" schemaparam) /
                   ;
                   ; The following is OPTIONAL,
                   ; and MAY occur more than once.
                   ;
                   (";" other-param)
                   ;
                )
Example:

The following is an example of this property:

  STRUCTURED-DATA;FMTTYPE=application/ld+json;
   SCHEMA="https://schema.org/SportsEvent";
   VALUE=TEXT:{\n
     "@context": "http://schema.org"\,\n
     "@type": "SportsEvent"\,\n
     "homeTeam": "Pittsburgh Pirates"\,\n
     "awayTeam": "San Francisco Giants"\n
   }\n

7. New Components

7.1. Participant

Component name:
PARTICIPANT
Purpose:
This component provides information about a participant in an event or task.
Conformance:
This component can be specified multiple times in a "VEVENT", "VTODO", "VJOURNAL" or "VFREEBUSY" calendar component.
Description:
This component provides information about a participant in a calendar component. A participant may be an attendee in a scheduling sense and the ATTENDEE property may be specified in addition. Participants can be individuals or organizations, for example a soccer team, the spectators or the musicians.
STRUCTURED-DATA properties if present may refer to definitions of the participant - such as a vCard.
The CALENDAR-ADDRESS property if present will provide a cal-address. If an ATTENDEE property has the same value the participant is considered schedulable. The PARTICIPANT component can be used to contain additional meta-data related to the attendee.
Format Definition:

This component is defined by the following notation:

   participantc = "BEGIN" ":" "PARTICIPANT" CRLF
                  partprop *locationc *resourcec
                  "END" ":" "PARTICIPANT" CRLF

   partprop     = *(
                  ;
                  ; The following are REQUIRED,
                  ; but MUST NOT occur more than once.
                  ;
                  participanttype / uid /
                  ;
                  ; The following are OPTIONAL,
                  ; but MUST NOT occur more than once.
                  ;
                  calendaraddress / created / description / dtstamp /
                  geo / last-mod / priority / seq /
                  status / summary / url /
                  ;
                  ; The following are OPTIONAL,
                  ; and MAY occur more than once.
                  ;
                  attach / categories / comment /
                  contact / location / rstatus / related /
                  resources / strucloc / strucres / styleddescription /
                  sdataprop / iana-prop
                  ;
                  )
Note:
When the PRIORITY is supplied it defines the ordering of PARTICIPANT components with the same value for the PARTICIPANT-TYPE property.
Privacy Issues:
When a LOCATION is supplied it provides information about the location of a participant at a given time or times. This may represent an unacceptable privacy risk for some participants. User agents MUST NOT broadcast this information without the express permission of the participants whose location would be exposed. For further comments see Section 10
Example:

The following is an example of this component. It contains a STRUCTURED-DATA property which points to a vCard providing information about the event participant.

   BEGIN:PARTICIPANT
   UID: em9lQGZvb2GFtcGxlLmNvbQ
   PARTICIPANT-TYPE:PERFORMER
   STRUCTURED-DATA;VALUE=URI:
    http://dir.example.com/vcard/aviolinist.vcf
   END:PARTICIPANT
Example:

The following is an example for the primary contact.

    BEGIN:PARTICIPANT
    UID: em9lQGZvb2GFtcGxlLmNvbQ
    STRUCTURED-DATA;VALUE=URI;
     http://dir.example.com/vcard/contacts/contact1.vcf
    PARTICIPANT-TYPE:CONTACT
    DESCRIPTION:A contact
    END:PARTICIPANT
Example:

The following is an example for a participant with contact and location.

    BEGIN:PARTICIPANT
    UID: em9lQGZvb2GFtcGxlLmNdrt
    STRUCTURED-DATA;VALUE=URI;
     http://dir.example.com/vcard/contacts/my-card.vcf
    PARTICIPANT-TYPE:SPEAKER
    DESCRIPTION:A participant
    BEGIN:VLOCATION
    UID:123456-abcdef-98765432
    NAME:My home location
    STRUCTURED-DATA;VALUE=URI:
     http://dir.example.com/addresses/my-home.vcf
    END:VLOCATION
    END:PARTICIPANT

7.1.1. Schedulable Participant

A PARTICIPANT component may represent someone or something that needs to be scheduled as defined for ATTENDEE in [RFC5545] and [RFC5546]. The PARTICIPANT component may also represent someone or something that is NOT to receive scheduling messages.

For backwards compatibility with existing clients and servers when used to schedule events and tasks the ATTENDEE property MUST be used to specify the sheduling parameters as defined for that property.

For other, future uses the CALENDAR-ADDRESS property MUST be used to specify those parameters.

A PARTICIPANT component is defined to be schedulable if

  • It contains a CALENDAR-ADDRESS property
  • That property value is the same as the value for an ATTENDEE property.

If both of these conditions apply then the participant defined by the value of the URL property will take part in scheduling operations as defined in [RFC5546].

An appropriate use for the PARTICIPANT component in scheduling would be to store SEQUENCE and DTSTAMP properties associated with replies from each ATTENDEE. A LOCATION property within the PARTICIPANT component might allow better selection of meeting times when participants are in different timezones.

7.2. Location

Component name:
VLOCATION
Purpose:
This component provides rich information about the location of an event using the structured data property or optionally a plain text typed value.
Conformance:
This component can be specified multiple times in a "VEVENT", "VTODO", "VJOURNAL", "VFREEBUSY" or "PARTICIPANT" calendar component.
Description:
There may be a number of locations associated with an event. This component provides detailed information about a location.
When used in a component the value of this property provides information about the event venue or of related services such as parking, dining, stations etc..
STRUCTURED-DATA properties if present may refer to representations of the location - such as a vCard.
Format Definition:

This component is defined by the following notation:

   locationc    = "BEGIN" ":" "VLOCATION" CRLF
                  locprop
                  "END" ":" "VLOCATION" CRLF

   locprop      = *(
                  ;
                  ; The following are REQUIRED,
                  ; but MUST NOT occur more than once.
                  ;
                  uid /
                  ;
                  ; The following are OPTIONAL,
                  ; but MUST NOT occur more than once.
                  ;
                  description / geo / loctype / name /
                  ;
                  ; The following are OPTIONAL,
                  ; and MAY occur more than once.
                  ;
                  sdataprop / iana-prop
The NAME property is defined in [RFC7986]
Example:

The following is an example of this component. It points to a venue.

   BEGIN:VLOCATION
   UID:123456-abcdef-98765432
   NAME:The venue
   STRUCTURED-DATA;VALUE=URI:
    http://dir.example.com/venues/big-hall.vcf
   END:VLOCATION

7.3. Resource

Component name:
VRESOURCE
Purpose:
This component provides a typed reference to external information about a resource or optionally a plain text typed value. Typically a resource is anything that might be required or used by a calendar entity and possibly has a directory entry.
Conformance:
This component can be specified multiple times in a "VEVENT", "VTODO", "VJOURNAL", "VFREEBUSY" or "PARTICIPANT" calendar component.
Description:
When used in a component this component provides information about resources used for the event such as rooms, projectors, conferencing capabilities.
The RESOURCE-TYPE value registry provides a place in which resource types may be registered.
STRUCTURED-DATA properties if present may refer to representations of the resource - such as a vCard.
Format Definition:

This component is defined by the following notation:

   resourcec    = "BEGIN" ":" "VRESOURCE" CRLF
                  resprop
                  "END" ":" "VRESOURCE" CRLF

   resprop      = *(
                  ;
                  ; The following are REQUIRED,
                  ; but MUST NOT occur more than once.
                  ;
                  uid /
                  ;
                  ; The following are OPTIONAL,
                  ; but MUST NOT occur more than once.
                  ;
                  description / geo / name / restype /
                  ;
                  ; The following are OPTIONAL,
                  ; and MAY occur more than once.
                  ;
                  sdataprop / iana-prop
The NAME property is defined in [RFC7986]
Example:

The following is an example of this component. It refers to a projector.

   BEGIN:VRESOURCE
   UID:456789-abcdef-98765432
   NAME:The projector
   RESOURCE-TYPE:projector
   STRUCTURED-DATA;VALUE=URI:http://dir.example.com/projectors/3d.vcf
   END:VRESOURCE

8. Extended examples

The following are some examples of the use of the properties defined in this specification. They include additional properties defined in [RFC7986] which includes IMAGE.

8.1. Example 1

The following is an example of a VEVENT describing a concert. It includes location information for the venue itself as well as references to parking and restaurants.

BEGIN:VEVENT
CREATED:20200215T145739Z
DESCRIPTION: Piano Sonata No 3\n
 Piano Sonata No 30
DTSTAMP:20200215T145739Z
DTSTART;TZID=America/New_York:20200315T150000Z
DTEND;TZID=America/New_York:20200315T163000Z
LAST-MODIFIED:20200216T145739Z
SUMMARY:Beethoven Piano Sonatas
UID:123456
IMAGE;VALUE=URI;DISPLAY=BADGE;FMTTYPE=image/png:h
 ttp://example.com/images/concert.png
BEGIN:PARTICIPANT
PARTICIPANT-TYPE:SPONSOR
UID:dG9tQGZvb2Jhci5xlLmNvbQ
STRUCTURED-DATA;VALUE=URI:http://example.com/sponsor.vcf
END:PARTICIPANT
BEGIN:PARTICIPANT
PARTICIPANT-TYPE:PERFORMER:
UID:em9lQGZvb2GFtcGxlLmNvbQ
STRUCTURED-DATA;VALUE=URI:http://www.example.com/people/johndoe.vcf
END:PARTICIPANT
BEGIN:VLOCATION
UID:123456-abcdef-98765432
NAME:The venue
STRUCTURED-DATA;VALUE=URI:http://dir.example.com/venues/big-hall.vcf
END:VLOCATION
BEGIN:VLOCATION
UID:123456-abcdef-87654321
NAME:Parking for the venue
STRUCTURED-DATA;VALUE=URI:http://dir.example.com/venues/parking.vcf
END:VLOCATION
END:VEVENT

8.2. Example 2

The following is an example of a VEVENT describing a meeting. One of the attendees is a remote participant.

BEGIN:VEVENT
CREATED:20200215T145739Z
DTSTAMP:20200215T145739Z
DTSTART;TZID=America/New_York:20200315T150000Z
DTEND;TZID=America/New_York:20200315T163000Z
LAST-MODIFIED:20200216T145739Z
SUMMARY:Conference planning
UID:123456
ORGANIZER:mailto:a@example.com
ATTENDEE;PARTSTAT=ACCEPTED;CN=A:mailto:a@example.com
ATTENDEE;RSVP=TRUE;CN=B:mailto:b@example.com
BEGIN:PARTICIPANT
PARTICIPANT-TYPE:ACTIVE:
UID:v39lQGZvb2GFtcGxlLmNvbQ
STRUCTURED-DATA;VALUE=URI:http://www.example.com/people/b.vcf
LOCATION:At home
END:PARTICIPANT
END:VEVENT

9. Security Considerations

This specification extends [RFC5545] and makes further use of possibly linked data. While calendar data is not unique in this regard it is worth reminding implementors of some of the dangers and safeguards.

9.1. URIs

See [RFC3986] for a discussion of the security considerations relating to URIs. Because of the issues discussed there and below, clients SHOULD NOT follow URIs and fetch content automatically, and should only do so at the explicit request of the user.

Fetching remote resources carries inherent risks. Connections must only be allowed on well known ports, using allowed protocols (generally just HTTP/HTTPS on their default ports). The URL must be resolved externally and not allowed to access internal resources. Connecting to an external source reveals IP (and therefore generally location) information.

A maliciously constructed iCalendar object may contain a very large number of URIs. In the case of published calendars with a large number of subscribers, such objects could be widely distributed. Implementations should be careful to limit the automatic fetching of linked resources to reduce the risk of this being an amplification vector for a denial-of-service attack.

9.2. Malicious Content

For the "STRUCTURED-DATA" property, agents need to be aware that a client could attack underlying storage by sending extremely large values and could attack processing time by uploading a recurring event with a large number of overrides and then repeatedly adding, updating and deleting structured data.

Agents should set reasonable limits on storage size and number of instances and apply those constraints. Calendar protocols should ensure there is a way to report on such limits being exceeded.

Malicious content could be introduced into the calendar server by way of the "STRUCTURED-DATA" property and propagated to many end users via scheduling. Servers SHOULD check this property for malicious or inappropriate content. Upon detecting such content, servers SHOULD remove the property,

9.3. HTML Content

When processing HTML content, applications need to be aware of the many security and privacy issues, as described in the IANA considerations section of [W3C.REC-html51-20171003]

10. Privacy Considerations

10.1. Tracking

Properties with a "URI" value type can expose their users to privacy leaks as any network access of the URI data can be tracked both by a network observer and by the entity hosting the remote resource. Clients SHOULD NOT automatically download data referenced by the URI without explicit instruction from users.

To help alleviate some of the concerns protocols and services could provide proxy services for downloading referenced data.

10.2. Revealing Locations

The addition of location information to the new participant component provides information about the location of participants at a given time. This information MUST NOT be distributed to other participants without those participant's express permission. Note that there may be a number of participants who may be unaware of their inclusion in the data.

Agents processing and distributing calendar data must be aware that it has the property of providing information about a future time when a given individual may be at a particular location, which could enable targeted attacks against that individual.

The same may be true of other information contained in the participant component. In general, revealing only as much as is absolutely necessary should be the approach taken.

For example, there may be some privacy considerations relating to the ORDER parameter, as it provides an indication of the organizer's perception of the relative importance of other participants.

11. IANA Considerations

11.1. Additional iCalendar Registrations

11.1.1. Properties

This document defines the following new iCalendar properties to be added to the registry defined in Section 8.2.3 of [RFC5545]:

Table 1
Property Status Reference
CALENDAR-ADDRESS Current RFCXXXX, Section 6.4
LOCATION-TYPE Current RFCXXXX, Section 6.1
PARTICIPANT-TYPE Current RFCXXXX, Section 6.2
RESOURCE-TYPE Current RFCXXXX, Section 6.3
STRUCTURED-DATA Current RFCXXXX, Section 6.6
STYLED-DESCRIPTION Current RFCXXXX, Section 6.5

11.1.2. Parameters

This document defines the following new iCalendar property parameters to be added to the registry defined in Section 8.2.4 of [RFC5545]:

Table 2
Property Parameter Status Reference
ORDER Current RFCXXXX, Section 5.1
SCHEMA Current RFCXXXX, Section 5.2
DERIVED Current RFCXXXX, Section 5.3

11.1.3. Components

This document defines the following new iCalendar components to be added to the registry defined in Section 8.3.1 of [RFC5545]:

Table 3
Component Status Reference
PARTICIPANT Current RFCXXXX, Section 7.1
VLOCATION Current RFCXXXX, Section 7.2
VRESOURCE Current RFCXXXX, Section 7.3

11.2. New Registration Tables

This section defines new registration tables for PARTICIPANT-TYPE and RESOURCE-TYPE values. These tables are updated using the same approaches laid down in Section 8.2.1 of [RFC5545]

This document creates new IANA registries for participant and resource types. IANA will maintain these registries and, following the policies outlined in [RFC8126], new tokens are assigned after Expert Review. The Expert Reviewer will generally consult the IETF GeoPRIV working group mailing list or its designated successor. Updates or deletions of tokens from the registration follow the same procedures. The expert review should be guided by a few common sense considerations. For example, tokens should not be specific to a country, region, organization, or company; they should be well- defined and widely recognized. The expert's support of IANA will include providing IANA with the new token(s) when the update is provided only in the form of a schema, and providing IANA with the new schema element(s) when the update is provided only in the form of a token. To ensure widespread usability across protocols, tokens MUST follow the character set restrictions for XML Names [3]. Each registration must include the name of the token and a brief description similar to the ones offered herein for the initial registrations contained this document:

11.2.1. Participant Types

The following table has been used to initialize the participant types registry.

Table 4
Participant Type Status Reference
ACTIVE Current RFCXXXX, Section 6.2
INACTIVE Current RFCXXXX, Section 6.2
SPONSOR Current RFCXXXX, Section 6.2
CONTACT Current RFCXXXX, Section 6.2
BOOKING-CONTACT Current RFCXXXX, Section 6.2
EMERGENCY-CONTACT Current RFCXXXX, Section 6.2
PUBLICITY-CONTACT Current RFCXXXX, Section 6.2
PLANNER-CONTACT Current RFCXXXX, Section 6.2
PERFORMER Current RFCXXXX, Section 6.2
SPEAKER Current RFCXXXX, Section 6.2

11.2.2. Resource Types

The following table has been used to initialize the resource types registry.

Table 5
Resource Type Status Reference
PROJECTOR Current RFCXXXX, Section 6.3
ROOM Current RFCXXXX, Section 6.3
REMOTE-CONFERENCE-AUDIO Current RFCXXXX, Section 6.3
REMOTE-CONFERENCE-VIDEO Current RFCXXXX, Section 6.3

12. Acknowledgements

The author would like to thank Chuck Norris of eventful.com for his work which led to the development of this RFC.

The author would also like to thank the members of CalConnect, The Calendaring and Scheduling Consortium, the Event Publication technical committee and the following individuals for contributing their ideas and support:

Cyrus Daboo, John Haug, Dan Mendell, Ken Murchison, Scott Otis.

13. Normative References

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC2426]
Dawson, F. and T. Howes, "vCard MIME Directory Profile", RFC 2426, DOI 10.17487/RFC2426, , <https://www.rfc-editor.org/info/rfc2426>.
[RFC3986]
Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, , <https://www.rfc-editor.org/info/rfc3986>.
[RFC4589]
Schulzrinne, H. and H. Tschofenig, "Location Types Registry", RFC 4589, DOI 10.17487/RFC4589, , <https://www.rfc-editor.org/info/rfc4589>.
[RFC5545]
Desruisseaux, B., Ed., "Internet Calendaring and Scheduling Core Object Specification (iCalendar)", RFC 5545, DOI 10.17487/RFC5545, , <https://www.rfc-editor.org/info/rfc5545>.
[RFC5546]
Daboo, C., Ed., "iCalendar Transport-Independent Interoperability Protocol (iTIP)", RFC 5546, DOI 10.17487/RFC5546, , <https://www.rfc-editor.org/info/rfc5546>.
[RFC7986]
Daboo, C., "New Properties for iCalendar", RFC 7986, DOI 10.17487/RFC7986, , <https://www.rfc-editor.org/info/rfc7986>.
[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, , <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, , <https://www.rfc-editor.org/info/rfc8174>.
[RFC8259]
Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, , <https://www.rfc-editor.org/info/rfc8259>.
[W3C.REC-html51-20171003]
Faulkner, S., Eicholz, A., Leithead, T., and A. Danilo, "HTML 5.1 2nd Edition", World Wide Web Consortium Recommendation REC-html51-20171003, , <https://www.w3.org/TR/2017/REC-html51-20171003>.
[W3C.REC-xml-20081126]
Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth Edition)", World Wide Web Consortium Recommendation REC-xml-20081126, , <https://www.w3.org/TR/2008/REC-xml-20081126>.

Appendix A. Open issues

None at the moment

Appendix B. Change log

To be deleted on publication

calext-v19 2021-03-25 MD

calext-v18 2021-??-?? MD

calext-v17 2021-01-03 MD

calext-v16 2019-10-09 MD

calext-v15 2019-10-08 MD

calext-v14 2019-06-11 MD

calext-v13 2019-05-26 MD

calext-v12 2019-02-28 MD

calext-v11 2019-02-27 MD

calext-v09 2018-08-30 MD

calext-v08 2018-07-06 MD

calext-v04 2017-10-11 MD

calext-v03 2017-10-09 MD

calext-v02 2017-04-20 MD

calext-v01 2017-02-18 MD

calext-v00 2016-08-?? MD

v06 2016-06-26 MD

v05 2016-06-14 MD

v04 2014-02-01 MD

v03 2013-03-06 MD

v02 2012-11-02 MD

v01 2012-10-18 MD Many changes.

2011-01-07

v00 2007-10-19 MD Initial version

Author's Address

Michael Douglass
Bedework
226 3rd Street
Troy, NY 12180
United States of America
URI: http://bedework.com