Event Publishing Extensions to iCalendarBedework226 3rd StreetTroyNY12180United States of Americamdouglass@bedework.comhttp://bedework.com
ART
iCalendarproperties
This specification updates RFC 5545 by
introducing a number of new iCalendar
properties and components that are of particular use for event
publishers and in social networking.
This specification also defines a new "STRUCTURED-DATA" property for
iCalendar (RFC 5545) 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 is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 7841.
Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
. Introduction
. Conventions Used in This Document
. Terms Used in This Document
. Components and Properties
. Typed References
. Use Cases
. Piano Concert Performance
. Itineraries
. Reserving Facilities
. Modifications to Calendar Components
. New Property Parameters
. Order
. Schema
. Derived
. New Properties
. Location Type
. Participant Type
. Resource Type
. Calendar Address
. Styled-Description
. Structured-Data
. New Components
. Participant
. Schedulable Participant
. Location
. Resource
. Extended Examples
. Example 1
. Example 2
. Security Considerations
. URIs
. Malicious Content
. HTML Content
. Privacy Considerations
. Tracking
. Revealing Locations
. IANA Considerations
. Additional iCalendar Registrations
. Properties
. Parameters
. Components
. Participant Types and Resource Types Registries
. Participant Types
. Resource Types
. Normative References
Acknowledgements
Author's Address
Introduction
The currently existing iCalendar standard lacks
useful methods for referencing additional, external information
relating to calendar components. Additionally, there is no standard
way to provide rich-text descriptions or metadata associated with
the event.
Current practice is to embed this information as links
in the description or to add nonstandard properties, as defined in
.
This document updates 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 the interchange of such information between
applications or systems (e.g., between clients, between client and server,
and between servers). Formats, such as vCard ,
are likely to be
most useful to the receivers of such events as they may be used
in other applications -- such as address books.
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
when, and only when, they appear in all capitals, as shown here.
The notation used in this memo is the ABNF notation of as
used by iCalendar . Any syntax elements shown below that
are not explicitly defined in this specification come from iCalendar .Terms Used in This Document
Event:
When the word 'event' (perhaps with a capitalized 'E') 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.
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 .
In a break with this 'convention', this specification defines
a number of components rather than properties. This
is a better match for the way
and JSON 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.
Typed References
The properties and components defined here can all reference
external metadata, 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
presenting additional, related information for the user.
As always, clients should exercise caution in following
references to external data.
The "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, or
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;
examples include address, region,
country, postal code, parking availability, nearby restaurants, and
the venue, among others. 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 "FMTTYPE" parameter applied to the "STRUCTURED-DATA" property, 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
(e.g,, a school sports team) and the inactive participants (e.g., the parents) in the event.
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.
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.
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 iCalendar Transport-independent Interoperability Protocol (iTIP) 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 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.
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 rental car businesses
at the destination.
The embedded location information can guide the traveler around the airport itself
or to their final destination. The contact information can provide
detailed information about the booking agent, airlines, car hire
companies, and hotel.
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 metadata. The "PARTICIPANT" component allows attendees to
specify their location.
Modifications to Calendar Components
The following changes to the syntax defined in iCalendar
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 and 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 and 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
New Property ParametersOrder
Parameter name:
ORDER
Purpose:
This parameter defines 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.
Schema
Parameter Name:
SCHEMA
Purpose:
This parameter specifies 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.
This parameter specifies 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, as well as a value created from the rtf value.
New Properties
This specification makes use of the "NAME" property,
which is defined in .
Location Type
Property Name:
LOCATION-TYPE
Purpose:
This property specifies 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
. New location
types SHOULD be
registered in the manner laid down in .
Participant Type
Property Name:
PARTICIPANT-TYPE
Purpose:
This property specifies the type of participant.
Value Type:
The value type for this property is TEXT. The
allowable values are defined below.
Property Parameters:
Nonstandard 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.
Resource Type
Property Name:
RESOURCE-TYPE
Purpose:
This property specifies 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.
Calendar Address
Property Name:
CALENDAR-ADDRESS
Purpose:
This property specifies the calendar address for a participant.
Value Type:
CAL-ADDRESS
Property Parameters:
IANA-registered or nonstandard 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)
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, nonstandard, 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 either be 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" components 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
.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
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, nonstandard, 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 the "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 are 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 include
different event types. By using standard schemas, interoperability
can be improved between calendar clients and noncalendaring
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
New ComponentsParticipant
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 metadata
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" property is supplied, it defines the ordering of
"PARTICIPANT" components with the same value for the
"PARTICIPANT-TYPE" property.
Privacy Issues:
When a "LOCATION" property 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 .
Example:
The following is an example of this component. It
contains a "STRUCTURED-DATA" property that 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
Schedulable Participant
A "PARTICIPANT" component may represent someone or something that
needs to be scheduled, as defined for ATTENDEE in
and . 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 scheduling
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 and
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 .
An appropriate use for the "PARTICIPANT" component in scheduling
would be to store "SEQUENCE" and "DTSTAMP" properties associated with
replies from each "ATTENDEE" property. A "LOCATION" property within the
"PARTICIPANT" component might allow better selection of meeting times
when participants are in different time zones.
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 .
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
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, and 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 .
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
Extended Examples
The following are some examples of the use of the properties defined in
this specification. They include additional properties defined in
, which includes "IMAGE".
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
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
Security Considerations
This specification extends 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.
URIs
See 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.
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.
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
.
Privacy ConsiderationsTracking
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.
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.
IANA ConsiderationsAdditional iCalendar RegistrationsProperties
This document defines the following iCalendar properties
that have been added to the "Properties" registry defined in :
Additions to the Properties Registry
Property
Status
Reference
CALENDAR-ADDRESS
Current
RFC 9073,
LOCATION-TYPE
Current
RFC 9073,
PARTICIPANT-TYPE
Current
RFC 9073,
RESOURCE-TYPE
Current
RFC 9073,
STRUCTURED-DATA
Current
RFC 9073,
STYLED-DESCRIPTION
Current
RFC 9073,
Parameters
This document defines the following iCalendar property parameters
that have been added to the "Parameters" registry defined in :
Additions to the Parameters Registry
Parameter
Status
Reference
ORDER
Current
RFC 9073,
SCHEMA
Current
RFC 9073,
DERIVED
Current
RFC 9073,
Components
This document defines the following iCalendar components that have been
added to the "Components" registry defined in :
Additions to the Components Registry
Component
Status
Reference
PARTICIPANT
Current
RFC 9073,
VLOCATION
Current
RFC 9073,
VRESOURCE
Current
RFC 9073,
Participant Types and Resource Types Registries
This section defines new registration tables for PARTICIPANT-TYPE
and RESOURCE-TYPE values. These tables are updated using the same
approaches laid down in .
This document creates new IANA registries for participant and resource
types.
IANA will maintain these registries and, following the policies
outlined in , 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 .
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.
Participant Types
Initial Contents of the Participant Types Registry
Participant Type
Status
Reference
ACTIVE
Current
RFC 9073,
INACTIVE
Current
RFC 9073,
SPONSOR
Current
RFC 9073,
CONTACT
Current
RFC 9073,
BOOKING-CONTACT
Current
RFC 9073,
EMERGENCY-CONTACT
Current
RFC 9073,
PUBLICITY-CONTACT
Current
RFC 9073,
PLANNER-CONTACT
Current
RFC 9073,
PERFORMER
Current
RFC 9073,
SPEAKER
Current
RFC 9073,
Resource Types
Initial Contents of the Resource Types Registry
Resource Type
Status
Reference
PROJECTOR
Current
RFC 9073,
ROOM
Current
RFC 9073,
REMOTE-CONFERENCE-AUDIO
Current
RFC 9073,
REMOTE-CONFERENCE-VIDEO
Current
RFC 9073,
Normative ReferencesKey words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.Uniform Resource Identifier (URI): Generic SyntaxA Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK]Location Types RegistryThis document creates a registry for describing the types of places a human or end system might be found. The registry is then referenced by other protocols that need a common set of location terms as protocol constants. Examples of location terms defined in this document include aircraft, office, and train station. [STANDARDS-TRACK]Augmented BNF for Syntax Specifications: ABNFInternet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK]Internet Calendaring and Scheduling Core Object Specification (iCalendar)This document defines the iCalendar data format for representing and exchanging calendaring and scheduling information such as events, to-dos, journal entries, and free/busy information, independent of any particular calendar service or protocol. [STANDARDS-TRACK]iCalendar Transport-Independent Interoperability Protocol (iTIP)This document specifies a protocol that uses the iCalendar object specification to provide scheduling interoperability between different calendaring systems. This is done without reference to a specific transport protocol so as to allow multiple methods of communication between systems. Subsequent documents will define profiles of this protocol that use specific, interoperable methods of communication between systems.The iCalendar Transport-Independent Interoperability Protocol (iTIP) complements the iCalendar object specification by adding semantics for group scheduling methods commonly available in current calendaring systems. These scheduling methods permit two or more calendaring systems to perform transactions such as publishing, scheduling, rescheduling, responding to scheduling requests, negotiating changes, or canceling. [STANDARDS-TRACK]vCard Format SpecificationThis document defines the vCard data format for representing and exchanging a variety of information about individuals and other entities (e.g., formatted and structured name and delivery addresses, email address, multiple telephone numbers, photograph, logo, audio clips, etc.). This document obsoletes RFCs 2425, 2426, and 4770, and updates RFC 2739. [STANDARDS-TRACK]New Properties for iCalendarThis document defines a set of new properties for iCalendar data and extends the use of some existing properties to the entire iCalendar object.Guidelines for Writing an IANA Considerations Section in RFCsMany protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA).To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry.This is the third edition of this document; it obsoletes RFC 5226.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.The JavaScript Object Notation (JSON) Data Interchange FormatJavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data.This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance.HTML 5.1 2nd EditionExtensible Markup Language (XML) 1.0 (Third Edition)Extensible Markup Language (XML) 1.0 (Fifth Edition)Acknowledgements
The author would like to thank 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:
, , , , and .
Author's AddressBedework226 3rd StreetTroyNY12180United States of Americamdouglass@bedework.comhttp://bedework.com