This specification updates
This specification also defines a new STRUCTURED-DATA property for iCalendar
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This specification updates
This specification also defines a new STRUCTURED-DATA property for iCalendar
The currently existing iCalendar standard
Current practice is to embed this information as links in the description or to add non-standard properties as defined in
This document updates
For the purposes of this document, the following terms and definitions apply.
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.
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.
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
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 ‘tradition’ this specification defines a number of components rather than properties. This is a better match for the way
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.
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
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.
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.
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
An event can also be created for publication which will have a PARTICIPANT component for the pianist providing a reference to vCard
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.
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.
The following changes to the syntax defined in
ORDER
To define ordering for the associated property.
This parameter is defined by the following notation:
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.
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
To specify the schema used for the content of a “STRUCTURED-DATA” property value.
This parameter is defined by the following notation:
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.
DERIVED
To specify that the value of the associated property is derived from some other property value or values.
This parameter is defined by the following notation:
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.
This specification makes use of the NAME property which is defined in
LOCATION-TYPE
To specify the type(s) of a location.
The value type for this property is TEXT. The allowable values are defined below.
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.
This property is defined by the following notation:
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
PARTICIPANT-TYPE
To specify the type of participant.
The value type for this property is TEXT. The allowable values are defined below.
Non-standard parameters can be specified on this property.
This property MUST be specified once within a PARTICIPANT component.
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.
This property is defined by the following notation:
The registered values for the PARTICIPANT-TYPE property have the meanings described here:
A participant taking an active role — for example a team member.
A participant taking an inactive role — for example an audience member.
A sponsor of the event. The ORDER parameter may be used with this participant type to define the relative order of multiple sponsors.
Contact information for the event. The ORDER parameter may be used with this participant type to define the relative order of multiple contacts.
Contact information for reservations or payment
Contact in case of emergency
Contact for publicity
Contact for the event planner or organizer
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 at an event
RESOURCE-TYPE
To specify the type of resource.
The value type for this property is TEXT. The allowable values are defined below.
This property is defined by the following notation:
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.
A room for the event/meeting.
Projection equipment.
Audio remote conferencing facilities.
Video remote conferencing facilities.
CALENDAR-ADDRESS
To specify the calendar address for a participant.
CAL-ADDRESS
IANA-registered, or non-standard property parameters can be specified on this property.
This property MAY be specified once within a PARTICIPANT component.
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.
This property is defined by the following notation:
STYLED-DESCRIPTION
This property provides for one or more rich-text descriptions to replace that provided by the DESCRIPTION property.
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.
IANA-registered, non-standard, id, alternate text representation, format type, derived and language property parameters can be specified on this property.
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.
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
Multiple STYLED-DESCRIPTION properties may be used to provide different formats or different language variants. However all but one MUST have DERIVED=TRUE.
This property is defined by the following notation:
The following is an example of this property. It points to an html description.
STRUCTURED-DATA
This property specifies ancillary data associated with the calendar component.
There is no default value type for this property. The value type can be set to TEXT, BINARY or URI
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.
This property can be specified multiple times in an iCalendar object. Typically it would be used in “VEVENT”, “VTODO” or “VJOURNAL” calendar components.
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 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.
This property is defined by the following notation:
The following is an example of this property:
PARTICIPANT
This component provides information about a participant in an event or task.
This component can be specified multiple times in a “VEVENT”, “VTODO”, “VJOURNAL” or “VFREEBUSY” calendar component.
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.
This component is defined by the following notation:
When the PRIORITY is supplied it defines the ordering of PARTICIPANT components with the same value for the PARTICIPANT-TYPE property.
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.
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.
The following is an example for the primary contact.
The following is an example for a participant with contact and location.
A PARTICIPANT component may represent someone or something that needs to be scheduled as defined for ATTENDEE in
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
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. A LOCATION property within the PARTICIPANT component might allow better selection of meeting times when participants are in different timezones.
VLOCATION
This component provides rich information about the location of an event using the structured data property or optionally a plain text typed value.
This component can be specified multiple times in a “VEVENT”, “VTODO”, “VJOURNAL”, “VFREEBUSY” or “PARTICIPANT” calendar component.
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.
This component is defined by the following notation:
The NAME property is defined in
The following is an example of this component. It points to a venue.
VRESOURCE
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.
This component can be specified multiple times in a “VEVENT”, “VTODO”, “VJOURNAL”, “VFREEBUSY” or “PARTICIPANT” calendar component.
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.
This component is defined by the following notation:
The NAME property is defined in
The following is an example of this component. It refers to a projector.
The following are some examples of the use of the properties defined in this specification. They include additional properties defined in
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.
The following is an example of a VEVENT describing a meeting. One of the attendees is a remote participant.
This specification extends
See
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.
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.
When processing HTML content, applications need to be aware of the many security and privacy issues, as described in the IANA considerations section of
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.
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.
This document defines the following new iCalendar properties to be added to the registry defined in
| Property | Status | Reference |
|---|---|---|
| CALENDAR-ADDRESS | Current | RFCXXXX, |
| LOCATION-TYPE | Current | RFCXXXX, |
| PARTICIPANT-TYPE | Current | RFCXXXX, |
| RESOURCE-TYPE | Current | RFCXXXX, |
| STRUCTURED-DATA | Current | RFCXXXX, |
| STYLED-DESCRIPTION | Current | RFCXXXX, |
This document defines the following new iCalendar property parameters to be added to the registry defined in
| Property Parameter | Status | Reference |
|---|---|---|
| ORDER | Current | RFCXXXX, |
| SCHEMA | Current | RFCXXXX, |
| DERIVED | Current | RFCXXXX, |
This document defines the following new iCalendar components to be added to the registry defined in
| Component | Status | Reference |
|---|---|---|
| PARTICIPANT | Current | RFCXXXX, |
| VLOCATION | Current | RFCXXXX, |
| VRESOURCE | Current | RFCXXXX, |
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
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:
The following table has been used to initialize the participant types registry:
| Participant Type | Status | Reference |
|---|---|---|
| ACTIVE | Current | RFCXXXX, |
| INACTIVE | Current | RFCXXXX, |
| SPONSOR | Current | RFCXXXX, |
| CONTACT | Current | RFCXXXX, |
| BOOKING-CONTACT | Current | RFCXXXX, |
| EMERGENCY-CONTACT | Current | RFCXXXX, |
| PUBLICITY-CONTACT | Current | RFCXXXX, |
| PLANNER-CONTACT | Current | RFCXXXX, |
| PERFORMER | Current | RFCXXXX, |
| SPEAKER | Current | RFCXXXX, |
The following table has been used to initialize the resource types registry:
| Resource Type | Status | Reference |
|---|---|---|
| PROJECTOR | Current | RFCXXXX, |
| ROOM | Current | RFCXXXX, |
| REMOTE-CONFERENCE-AUDIO | Current | RFCXXXX, |
| REMOTE-CONFERENCE-VIDEO | Current | RFCXXXX, |
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.
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
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This memo defines the profile of the MIME Content-Type for directory information for a white-pages person object, based on a vCard electronic business card. [STANDARDS-TRACK]
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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]
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.
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JavaScript 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.
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