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Internet calsify The Internet Calendaring and Scheduling Core Object Specification (iCalendar) (RFC5545) VTODO calendar component has seen limited adoption and use, mainly for personal reminders and to-do lists. This document updates and defines extensions to VTODO to provide improved status tracking, scheduling and specification of tasks to allow its use in other contexts, such as process control and project management. It also defines how Calendaring Extensions to WebDAV (CalDAV) (RFC 4791) servers can be extended to support certain automated task management behaviours.

Introduction This document specifies extensions to the Internet Calendaring and Scheduling Core Object Specification (iCalendar) , and associated protocols, in order to enhance the structured communication and execution of tasks. The enhancements allow for the communication, time planning and scheduling of tasks by and between automated systems (e.g. taxi dispatch systems, in smart power grids (see ), business process management systems) as well as for human centered tasks. A "task" is a representation of an item of work assigned to an individual or organization. In the iCalendar Object Model the representation of tasks is by "VTODO" calendar components. Tasks can be identified in a number of situations, either informally as ad-hoc tasks in personal "to-do" lists or more formally in: Business processes - ranging from repetitive workflows to adaptive cases and trouble ticketing Project Management - whether for large scale construction projects or collaborative software development The extensions specified in this document enhance and standardize the following:

The specification of tasks:

how a task type is defined and the relationships between tasks See .

Task planning and scheduling:

Improved specification of deadlines and estimated time for completion. See

Task assignment and status reporting:

The addition of VSTATUS, () allows for more detailed reports. See .

These extensions are defined within the context of an overall architecture for task calendaring and scheduling, which elaborates that supported by and related standards.

Terms and Definitions 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 to (re-)define iCalendar elements is the ABNF notation of as used by . Any syntax elements shown below that are not explicitly defined in this specification come from iCalendar . Calendaring and scheduling roles are referred to in quoted-strings of text with the first character of each word in upper case. For example, "Organizer" refers to a role of a "Calendar User" (CU) within the scheduling protocol. Calendar components defined by and updating specifications are referred to with capitalized, quoted-strings of text, followed by the words "calendar component". For example, "VEVENT" calendar component refers to the event calendar component, "VTODO" calendar component refers to the to-do calendar component, and "VJOURNAL" calendar component refers to the daily journal calendar component. Scheduling methods are referred to with capitalized, quoted-strings of text. For example, "REQUEST" refers to the method for requesting a scheduling calendar component be created or modified; "REPLY" refers to the method a recipient of a request uses to update their status with the "Organizer" of the calendar component. Properties defined by and updating specifications are referred to with capitalized, quoted-strings of text, followed by the word "property". For example, "ATTENDEE" property refers to the iCalendar property used to convey the calendar address of a "Calendar User". Property parameters defined by and updating specifications are referred to with lowercase, quoted-strings of text, followed by the word "parameter". For example, "value" parameter refers to the iCalendar property parameter used to override the default data type for a property value. Enumerated values defined by this specification are referred to with capitalized text, either alone or followed by the word "value". In tables, the quoted-string text is specified without quotes in order to minimize the table length. Terms defined and used in this specification include:

Assignee:

A calendar user assigned to perform a given task. An assignee is equivalent to an "Attendee" of a task.

BPMS:

Business Process Management Software

Calendar User (CU):

A person or software system that accesses or modifies calendar information.

Calendar User Agent (CUA):

This may be

1. Software with which the calendar user communicates with a calendar service or local calendar store to access calendar information.
2. Software that gathers calendar data on the Calendar User's behalf.

Candidate:

A calendar user who might be able to perform a given task, prior to actually being assigned the task, e.g., a dispatcher has a list of taxi drivers (candidates) from which one will be selected to pick-up a passenger.

Organizer:

A calendar user who creates a calendar item, requests free/busy information, or published free/busy information. It is an "Organizer" who invites "Attendees" .

Observer:

A calendar user interested in a calendar component, e.g., a manager may have interest in all tasks that have not been completed. Often represented as an "Attendee" with the "role" parameter set to NON-PARTICIPANT.

Resource:

A resource in the scheduling context is any shared entity that can be scheduled by a calendar user, but does not control its own attendance status. Examples of such resources are locations such as a bookable conference room or equipment such as projectors.

Task:

A representation of an item of work that can be assigned to one or more task actor assignees. In , these are "VTODO" calendar components, which are groupings of component properties and possibly "VALARM" calendar components that represent an action-item or assignment.

Task Architecture A reference architecture for task calendaring and scheduling is defined in order to identify the key logical elements involved in task management and the interfaces between them to enable interoperability. Central to this architecture is the Calendar and Scheduling System. The logical elements identified here establish an appropriate separation of concerns and clarify the responsibilities of different elements. However, the architecture does not prescribe a binding or packaging of elements, i.e., software systems may be developed where some elements are tightly bound and the interfaces between bound elements are not exposed. The task architecture is also described in .

Task architecture diagram | | +-^--------^--------------+ | | | | | | | | | | +--------V-+ +----V-----+ +----------+ | | | | | Task | | Process | | Task | | | | | |Assignment| | Logic <----> Domain | | | | | | Rules | | | | Data | | | | | +----------+ +----------+ +----------+ | | | | | | | +------^----------+-----^-------------------+ | | | | | | | Availability Task Task | | | | Status | | | | | | | +------v----------v-----+-------------------+ | | | Calendar and Scheduling System | | Directory | | +---------+ +---------+ | | Service | | | | | Task | <----> | | |Schedule | | Lists | | | | | | | | | | | | | +---------+ +---------+ Server | | | +-------------------------------------------+ | | | Client | | | | +----------------------+ +-----------+ | | | | | Calendar | | Task | | | | | | User Agent +----> Specific | <----> | | | | |Application| | | | | +----------------------+ +-----------+ | | | | | | | +-----^---------^--------+---------+--------+ | | | | | | | | +-----V---------V--------V---------V--------+ | | | Task Actors | | | | O O O O | | | | /|\ /|\ /|\ /|\ +----> | | / \ / \ / \ / \ | | | | Candidate(s) Observer(s) | | | | Assignee(s) Resource(s) | | | +-------------------------------------------+ +-----------+]]>

Task Architecture Elements The following logical elements form the task architecture that this specification is based on:

Task Actors:

Various calendar users that may be involved in the monitoring or performing of a task. The set of actors includes: Organizers, Observers, Resources, Assignees, and Candidates.

Task Organizer:

The creator of a task, who also determines task assignment and scheduling, and monitors task progress.

Task Domain Data:

This is any domain specific data that may be acted on or provides context to it in performing a task.

Task Specific Application:

A task specific application renders the data concerning the task (including task domain data) for presentation and manipulation by a task actor.

Process Logic:

Determines under what conditions a task (or tasks) is generated and the actions to take on completion, or some other status event occurring (or not) on the task.

Task Trigger:

This is some event that gives rise to the generation of a task according to Process Logic. Task triggers can come from many sources including, for example; a task being requested through the calendaring system, a status change in the progression of a business process being managed by a business process management or Enterprise resource planning (ERP) system.

Task Assignment Rules:

Govern how actors are assigned to a task. A range of different assignment patterns may be considered, including the two general cases:

1. Delegation to a named actor or group of actors
2. Advertising to a pool of actors for self-selection

In either case the assignment may be made based on a variety of criteria including, name, availability, skills, capacity, etc.

Task Generating System:

A system that creates and assigns tasks in response to some initiating event (task trigger). Task creation is according to Process Logic with task assignment determined by Task Assignment Rules. This system also tracks the status of tasks and will initiate further actions based upon the status. A task generating system can take many forms, for example; Business Process Management System, Project Management System, Bug Tracking System, Building Control System. A Task Generating System may also be a human. In iCalendar terms the Task Generating System is the organizer. Task creation, assignment and tracking coordinated by a human organizer is a special case of a task generating system. In this case Task Assignment Rules and Process Logic may be either explicit or tacit.

Calendar and Scheduling System:

A software system that stores, publishes and synchronizes calendar data such as events, tasks and journal entries for actors. In the context of tasks this includes schedules (i.e. allocated time and availability to perform tasks) and task lists. A calendar and scheduling system typically consists of server and client software components.

It is not within the scope of this document to specify how Process Logic or Task Assignment Rules are codified. Such logic and rules may be codified in a variety of ways, including traditional programming languages (e.g. C++, Java) or process modelling languages (e.g. BPMN ).

Architecture Foundations The key standards that enable interoperability between the logical elements of the architecture are the Internet Calendaring and Scheduling Core Object Specification (iCalendar) and associated protocols. Task and task status are represented by the "VTODO" calendar component. Protocols include, in particular, the iCalendar Transport-Independent Interoperability Protocol (iTIP) for task assignment and scheduling, and Calendaring Extensions to WebDAV (CalDAV) for client server communication. Additionally, this specification uses definitions from Support for iCalendar Relationships . The "LINK", "REFID", "RELATED-TO" and "CONCEPT" properties enable context and a rich set of relationships between tasks and other calendar components to be specified.

Task Extensions In order to support the task architecture described in , this document defines a number of extensions to iCalendar in the areas of:

Task Specification:

improved ability to specify domain specific tasks

Task Deadlines, Milestones and Time Planning:

clarification of deadlines and extension for task duration to support task time planning

Task Scheduling and Assignment:

ensure support for common patterns of scheduling and assigning tasks

Task Status Tracking:

improved granularity in status tracking information and alerting task actors of pending or actual task status changes

These extensions are supported mainly by additions to the properties and parameters used within the "VTODO" calendar component.

Task Specification The specification of tasks must be semantically explicit in order for them to be managed within the context of a business process or project, and be understood by both humans and IT systems. The "VTODO" calendar component only provides for simple ad-hoc tasks or 'to do' lists, and is therefore extended by this specification as follows:

Task type:

explicitly what type of task is to be performed is identified.

Task context and relationships:

how a specific task relates to other tasks and other objects that need to be understood for the effective execution of a task.

Task specific data:

the form and content of domain data provided as input to a task and/or that may be output from a task.

Organizer and attendee:

recognizes that a task "Organizer" or "Attendee" can be an automated system.

Task type The "CONCEPT" property is used to identify the type of task, for example;

Task Context and Relationships The "LINK" property specifies a link to external information, which may be context to the task. For example: The external information may be data to be manipulated in performing the task. The "LINK" property can be used to relate a domain specific service to the task. For example, it might be a URI pointing to a web page where the status of the task can be directly manipulated. (Note: link relations below are for illustration only) Additionally, it might be used to link data specific to the task, for example an electronic copy of a signature taken to confirm delivery of a package. The "REFID" property is used to identify a key used to group tasks by that key. Extensions to the "RELATED-TO" property defined in allow temporal relationships between tasks as found in project management to be specified as well as parent/child relationships and dependencies (DEPENDS-ON). Tasks ("VTODO" calendar components) may also be related to other calendar components; for example to a "VEVENT" calendar component to block time to perform a task.

Task Deadlines, Milestones and Time Planning

Deadlines Deadlines for starting and finishing a task are defined by the "DTSTART", "DUE" and "DURATION" properties. The "DTSTART" property represents the earliest start time for beginning work on a task. The "DUE", or "DTSTART" + "DURATION" properties represent the latest finish time for a task. Thus, these properties define a "window" within which a task has to be performed. However, provides no way to indicate how long the task is expected to take. This document defines a new "ESTIMATED-DURATION" property, in , to allow the estimated time that a task should take to be specified separately from the deadlines for starting and finishing a task. This supports time planning by enabling calendar user agents to display when tasks should occur and therefore allow calendar users to visualize when tasks should be performed and allocate time to them.

Milestones A task that has intermediary deadlines (i.e., milestones) MUST be expressed by child "VTODO" calendar components (i.e., sub-tasks associated with each of the milestones) in conjunction with the "RELATED-TO" property to relate the parent and child tasks.

Task Scheduling and Assignment Tasks are assigned to actors using one or more "ATTENDEE" properties and/or one or more "PARTICIPANT" calendar components as described in . Communication of task assignment or delegation to one or more actors who are allocated to a task by the organizer is directly supported by iTIP, i.e., all included "ATTENDEE" properties in an iTIP "REQUEST" are expected to perform the task. The offering or advertising of a task to one or more (potential) actors where only one or a subset of the candidates may accept the task will be addressed by a later specification.

Status Reporting

Improved granularity in status reporting information This document defines a new "VSTATUS" calendar component (see section ) that can be used to group related information about the status of the task. This might include information on why, the "REASON" property and when, the "DTSTAMP" property, a status has changed. In addition, new status values are specified to provide for task suspension, failure and preparation.

Comments associated to reasons and status changes Multiple comments and reasons may have the same status. As situations change, further "VSTATUS" calendar components can be added to provide additional information. Note that the "VSTATUS" calendar component is not intended to be used as a history of changes to a tasks properties. The purpose of the "VSTATUS" calendar component is only to document changes related to fulfilling the tasks.

Updating the overall status Only the Task Organizer, or the server acting as the Organizers proxy, may change or add "VSTATUS" calendar components and the "STATUS" property. The overall VSTATUS will be changed in response to incoming Attendee replies. Each change of the overall VSTATUS MUST be accompanied by a change to the STATUS. Note there is no defined ordering of properties and components so the DTSTAMP property SHOULD be set for each VSTATUS component to preserve ordering.

Relating reason and comments to "ATTENDEE" property status changes. The "PARTICIPANT" calendar component can be used to provide additional information about why an "ATTENDEE" property participation status has changed following the guidelines set out in . The "COMMENT" property can also be used to include additional human-readable information about why the associated "STATUS" or "ATTENDEE" property changed. For example, if a driver failed to deliver a package because of a puncture it might be expressed as

Task Alerts and Notifications Different needs to alert or notify task actors of pending or actual task status changes are recognized:

Alarms:

"VALARM" calendar components operate in the calendar user agent space to notify the task actor of a pending task state for a task they are assigned to or are interested in. Current standards (see ) indicate "VALARM" calendar components SHOULD be removed from incoming data and many systems in fact do so. In a task assignment scenario it may be appropriate for the organizer to be able to set alarms for the participants. A system implementing these standards may choose to preserve "VALARM" calendar components but sending a task via some external service may result in them being removed. This issue is not addressed by this specification.

Escalations:

An escalation or notification to the "Attendee", "Organizer", or other task actor may be required if a deadline associated with a task is exceeded or for some other reason. Process Logic identifying when and who to propagate escalations is the responsibility of the Task Generating System, e.g., a BPMS.

Notifications:

Task actors (observers) not directly involved in performing a task, but with a known interest in a given task's status, can be identified by the "PARTICIPANT" calendar component against certain components e.g. the "VALARM" calendar component, to identify which task events the stakeholder/party is interested in. Notifications on shared calendars will allow task actors to register an interest in changes to tasks within a calendar (see ).

Automated Status Changes A new "TASK-MODE" property is introduced to instruct servers to apply automated operations for changing the status of a task.

Modifications to Calendar Components The following changes to the syntax defined in iCalendar and Event Publishing Extensions to iCalendar are made here. New elements are defined in subsequent sections.

New Parameter Values

Redefined VTODO Participant Status Participant status parameter type values are defined in . This specification redefines that type to include the new value FAILED for "VTODO" calendar components.

Format Definition:

This property parameter is redefined by the following notation which adds the value "FAILED":

Example:

New Properties

Estimated Duration

Property Name:

ESTIMATED-DURATION

Purpose:

This property specifies the estimated positive duration of time the corresponding task will take to complete.

Value Type:

DURATION

Property Parameters:

IANA and non-standard property parameters can be specified on this property.

Conformance:

This property can be specified in "VTODO" calendar components.

Format Definition:

This property is defined by the following notation:

Description:

In a "VTODO" calendar component the property MAY be used to specify the estimated duration for the to-do, with or without an explicit time window in which the event should be started and completed. When present, "DTSTART" and "DUE" or "DTSTART" and "DURATION" properties represent the window in which the task can be performed. The "ESTIMATED-DURATION" property SHOULD be passed from the organizer to the "Attendee" in iTIP messages.

Example:

The following is an example of this property that estimates the duration of a task to be one hour:

Reason

Property name:

REASON

Purpose:

To indicate the reason for a status change or change of "Attendee" participation status.

Value Type:

URI

Property Parameters:

IANA and non-standard property parameters can be specified on this property.

Conformance:

This property can be specified in "VSTATUS" and "PARTICIPANT" calendar components.

Format Definition:

This property is defined by the following notation:

Description:

This property allows the change in status of a task or participant status to be qualified by the reason for the change with a codified reason. Typically, reasons are defined within the context of the task type and therefore SHOULD include the name-space of the authority defining the task.

Example:

Substate

Property name:

SUBSTATE

Purpose:

To provide additional granularity of task status for e.g. IN-PROCESS.

Value Type:

TEXT

Property Parameters:

IANA and non-standard property parameters can be specified on this property.

Conformance:

This property can be specified in a "VSTATUS" calendar component.

Format Definition:

This property is defined by the following notation:

Description:

The substate property allows additional qualification and granularity of states to be recorded, in particular for the IN-PROCESS state. It allows individual substates to be recorded without the need to define and publish a subtask associated with a parent task purely to track that a particular state has been reached. This property also allows parallel states to be expressed, e.g. that a task has been suspended at whatever state it has reached.

Example:

Task Mode

Property Name:

TASK-MODE

Purpose:

This property specifies automatic operations that servers acting on behalf of the organizer apply to tasks based on changes in attendee status (PARTSTAT).

Value Type:

TEXT

Property Parameters:

IANA and non-standard property parameters can be specified on this property.

Conformance:

This property can be specified zero or once in a "VTODO" calendar component.

Format Definition:

This property is defined by the following notation:

Description:

In a "VTODO" calendar component this property MAY be used to indicate to servers how they can automatically change the state of the task based on iTIP replies from "Attendees". For example, the server can automatically set the overall task status to COMPLETED when every attendee has marked their own status (PARTSTAT) as COMPLETED, or the server could mark the task as FAILED if its DUE date passes without it being completed. TASK-MODE processing is performed on the organizer's copy of the task. To set the status, add a VSTATUS component as specified in . The property value is an IANA registered token that defines the mode to be used for the task. The modes are described in the following subsections. If the "TASK-MODE" property is absent then the "CLIENT" value is assumed.

AUTOMATIC-COMPLETION Task Mode:

The task mode value "AUTOMATIC-COMPLETION" indicates to the server that it SHOULD change the "VTODO" calendar component's status to "COMPLETED" as soon as all attendees in the task have replied with a "partstat" parameter set to "COMPLETED". Failing the task MUST be handled by a client.

AUTOMATIC-FAILURE Task Mode:

The task mode value "AUTOMATIC-FAILURE" indicates to the server that it SHOULD change the "VTODO" calendar component's status to "FAILED" if either:

1. the PARTSTAT of one "ATTENDEE" property is set to FAILED; or
2. the current time is past the effective due date of the component and the task has not yet been completed. The effective due date is either the "DUE" property value or the combination of the "DTSTART" and "DURATION" property values. Completing the task MUST be handled by a client.

AUTOMATIC Task Mode:

This mode handles the automatic behavior of both "AUTOMATIC-COMPLETION" and "AUTOMATIC-FAILURE".

CLIENT Task Mode:

The task mode value "CLIENT" is an instruction to the server to honour the status set by the client.

SERVER Task Mode:

The task mode value "SERVER" indicates to the server that it SHOULD change the "VTODO" calendar component's status to an appropriate value, based on implementation defined "business rules", as attendee responses are processed or as deadlines related to the task pass.

Examples:

Property Extensions and Clarifications

Updated DURATION Property definition for VTODO section 3.6.2 introduced a constraint on the use of the "DURATION" property in the "VTODO" calendar component, requiring that a "DURATION" property MUST be accompanied by a "DTSTART" property. This constraint is dropped reverting to the situation as specified previously. Thus the text: is replaced by This allows a "VTODO" calendar component to only have a "DURATION" property. Furthermore, the following text: is replaced by

Redefined STATUS Property The Status property is defined in . This specification extends that property to include new values associated with "VTODO" calendar components (See Appendix A for examples of the task state lifecycle).

Format Definition:

The "STATUS" property parameter list for tasks is redefined by the addition of the values "PENDING" and "FAILED":

Description: PENDING - A to-do has been created and accepted but has not yet started and is ready to start subject to other dependencies (e.g. preceding task or DTSTART). This is the default state. FAILED - to-do has failed and may need some follow-up from the organizer to re-schedule or cancel Example: The following is an example of this property for a "VTODO" calendar component:

New Components

Status Component

Component Name:

VSTATUS

Purpose:

This component allows information to be associated with a status, for example comments and date stamps.

Conformance:

This component can be specified multiple times in any calendar component.

Description:

This component provides a way for multiple date-stamped statuses to be associated with a component such as a participant, task or event.

This component may be added to the "PARTICIPANT" component to allow participants in a task to specify their own status. For backwards compatibility, when a VSTATUS component is added the STATUS property MUST be set on the parent component.

Format Definition:

This component is defined by the following notation:

Examples:

CalDAV Support for Task Mode The CalDAV calendar access protocol allows clients and servers to exchange iCalendar data. With the introduction of the "TASK-MODE" property in this specification, different automated task management behaviours may be delegated to the server by the Task Organizer depending upon the value of "TASK-MODE". In order for a CalDAV client to know what task modes are available, a CalDAV server advertises a CALDAV:supported-task-mode-set WebDAV property on calendar home or calendar collections if it supports the use of the "TASK-MODE" property as described in this specification. The server can advertise a specific set of supported task modes by including one or more CALDAV:supported-task-mode XML elements within the CALDAV:supported-task-mode-set XML element. If no CALDAV:supported-task-mode XML elements are included in the WebDAV property, then clients MUST assume the server does not support this specification. The client MAY attempt to store iCalendar data containing "TASK-MODE" elements but needs to be prepared for a failure response from the server. A server supporting this specification MUST return an HTTP 403 response with a DAV:error element containing a CALDAV:supported-task-mode XML element, if a client attempts to store iCalendar data with an "TASK-MODE" element value not supported by the server. It is possible for a "TASK-MODE" value to be present in calendar data on the server being accessed by a client that does not support the "TASK-MODE" property. It is expected that existing clients, unaware of "TASK-MODE", will fail gracefully by ignoring the calendar property.

CALDAV:supported-task-mode-set Property

Name:

supported-task-mode-set

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

Enumerates the set of supported iCalendar "TASK-MODE" element values supported by the server.

Protected:

This property MUST be protected and SHOULD NOT be returned by a PROPFIND allprop request (as defined in Section 14.2 of ).

Description:

See above.

Definition:

]]>

Example:

AUTOMATIC SERVER CLIENT ]]>

Security Considerations This specification introduces no new security considerations beyond those identified in , , and .

IANA Considerations

Component Registrations This document defines the following new iCalendar component to be added to the Components registry defined in and located here: <>. Addition to the Components Registry

Component	Status	Reference
VSTATUS	Current	This Spec,

Property Registrations This document defines the following new iCalendar properties to be added to the Properties registry defined in and located here: <>. Additions to the Properties Registry

Property	Status	Reference
ESTIMATED-DURATION	Current	This Spec,
REASON	Current	This Spec,
SUBSTATE	Current	This Spec,
STATUS	Current	This Spec,
TASK-MODE	Current	This Spec,

Status Value registry This document requests the creation of a new iCalendar registry called "STATUS Values" for values of the "STATUS" property defined in . Additional values MAY be used, provided the process of "Standards Action with Expert Review" as described in Section 8.2.1 of [RFC5545] is used to register them, using the template in Section 8.2.6 of [RFC5545]. The following table has been used to initialize the Status Value Registry. Initial Status Value Registry

Name	Status	Reference
CANCELLED	Current
COMPLETED	Current
CONFIRMED	Current
DRAFT	Current
FAILED	Current	This Spec,
FINAL	Current
IN-PROCESS	Current
NEEDS-ACTION	Current
PENDING	Current	This Spec,
TENTATIVE	Current

Substate Value registry This document requests the creation of a new iCalendar registry called "SUBSTATE Values" for values of the "SUBSTATE" property defined in . Additional values MAY be used, provided the process of "Standards Action with Expert Review" described in Section 8.2.1 of [RFC5545] is used to register them, using the template in Section 8.2.6 of [RFC5545]. The following table has been used to initialize the Substate Value Registry. Initial Substate Value registry

Substate	Status	Reference
OK	Current	This Spec,
ERROR	Current	This Spec,
SUSPENDED	Current	This Spec,

Task Mode Value registry This document requests the creation of a new iCalendar registry called "TASK-MODE Values" for values of the "TASK-MODE" property defined in . Additional values MAY be used, provided the process of "Standards Action with Expert Review" described in Section 8.2.1 of [RFC5545] is used to register them, using the template in Section 8.2.6 of [RFC5545]. The following table has been used to initialize the Task Mode Value Registry. Task Mode Value Registry

Task Mode	Status	Reference
AUTOMATIC-COMPLETION	Current	This Spec,
AUTOMATIC-FAILURE	Current	This Spec,
AUTOMATIC	Current	This Spec,
CLIENT	Current	This Spec,
SERVER	Current	This Spec,

Participation Statuses registry This document defines the following new iCalendar participation status to be added to the registry defined in Section 8.3.7 of [RFC5545] and located here: <> Participation Statuses Registry

Participation Status	Status	Reference
FAILED	Current	This Spec,

Acknowledgements The authors would like to thank the members of the Calendaring and Scheduling Consortium technical committees and the following individuals for contributing their ideas, support and comments: John Chaffee, Marten Gajda, Ken Murchison The authors would also like to thank CalConnect, the Calendaring and Scheduling Consortium, for advice with this specification.

Normative References IETF StandardsTrackDocuments In 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. IETF calschedcalschcalcavcalendarcalendaringschedulingwebdavicalicalendaritiptext/calendarhttp This document defines extensions to the Web Distributed Authoring and Versioning (WebDAV) protocol to specify a standard way of accessing, managing, and sharing calendaring and scheduling information based on the iCalendar format. This document defines the "calendar-access" feature of CalDAV. [STANDARDS-TRACK] IETF WEBDAVhypertexttransferprotocolwebcontent Web Distributed Authoring and Versioning (WebDAV) consists of a set of methods, headers, and content-types ancillary to HTTP/1.1 for the management of resource properties, creation and management of resource collections, URL namespace manipulation, and resource locking (collision avoidance). RFC 2518 was published in February 1999, and this specification obsoletes RFC 2518 with minor revisions mostly due to interoperability experience. [STANDARDS-TRACK] IETF ABNFbackus-naur formaugmented backus-naur formrule definitionsencodingcore lexical analyzer Internet 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] IETF calsifycalschedcalschcaldavcalendarcalendaringmeetingeventtaskto-dojournalappointmentagendascheduleschedulingicalicalendaritipimiptext/calendarischedulexCalendar 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] IETF calendarscheduling 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] IETF RFC 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. IETF 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. IETF alarmscalendaringiCalendarCalDAV This document defines a set of extensions to the iCalendar "VALARM" component to enhance the use of alarms and improve interoperability between clients and servers. This document updates RFC 5545. IETF iCalendarlinkrelated-torelationships This specification updates the iCalendar RELATED-TO property defined in RFC 5545 by adding new relation types and introduces new iCalendar properties (LINK, CONCEPT, and REFID) to allow better linking and grouping of iCalendar components and related data. Informative References Business ModelingDomain Business Process Model and Notation has become the de-facto standard for business processes diagrams. It is intended to be used directly by the stakeholders who design, manage and realize business processes, but at the same time be precise enough to allow BPMN diagrams to be translated into software process components. BPMN has an easy-to-use flowchart-like notation that is independent of any particular implementation environment. OMG BPMN 2.0.2 (CalConnect Task Architecture V1.0 WsCalendar WfRP

Examples of Task State Lifecycle

Simple Case Status Change Example of status changes in assigning and performing a task with one attendee.

	STATUS	PARTSTAT	Action
1	-	-	Organizer draft
2	NEEDS-ACTION	NEEDS-ACTION	Organizer sends iTIP "REQUEST"
3	NEEDS-ACTION	ACCEPTED	Attendee "REPLY"
4	PENDING	ACCEPTED	Task accepted but waiting on some "trigger" to start (e.g. another task has to finish first)
5	IN-PROCESS	IN-PROCESS	Attendee "REPLY" now working on the task
6	IN-PROCESS	COMPLETED	Attendee "REPLY" completed
7	COMPLETED	COMPLETED	Overall state set - either by Organizer for TASK-MODE=CLIENT or by server for AUTOMATIC-COMPLETION

Example for multiple Attendees Example of status changes in assigning and performing a task with two attendees (A1 and A2). Example for multiple Attendees

	STATUS	PARTSTAT (A1)	PARTSTAT (A2)	Action
1	-	-	-	Organizer draft.
2	NEEDS-ACTION	NEEDS-ACTION	NEEDS-ACTION	Organizer sends iTIP "REQUEST".
4	NEEDS-ACTION	ACCEPTED	NEEDS-ACTION	Attendee 1 "REPLY".
5	NEEDS-ACTION	ACCEPTED	ACCEPTED	Attendee 2 "REPLY".
6	PENDING	ACCEPTED	ACCEPTED	Task accepted but waiting on some"trigger" to start (e.g. another task has to finish first)
7	IN-PROCESS	ACCEPTED	IN-PROCESS	Attendee 2 "REPLY" now working on the task.
8	IN-PROCESS	IN-PROCESS	IN-PROCESS	Attendee 1 "REPLY" now working on the task.
9	IN-PROCESS	COMPLETED	IN-PROCESS	Attendee 1 "REPLY" Completed (overall status still IN-PROCESS).
10	IN-PROCESS	COMPLETED	COMPLETED	Attendee 2 "REPLY" Completed
11	COMPLETED	COMPLETED	COMPLETED	Overall state set once both attendees are finished. May be set by Organizer for TASK-MODE=CLIENT or by server for AUTOMATIC-COMPLETION

Example of Failure Example of status changes for a task that fails. Example of Failure

	STATUS	PARTSTAT	Action
1	-	-	Organizer draft
2	NEEDS-ACTION	NEEDS-ACTION	Organizer sends iTIP "REQUEST"
3	NEEDS-ACTION	ACCEPTED	Attendee "REPLY"
4	IN-PROCESS	IN-PROCESS	Attendee "REPLY" now working on the task
5	IN-PROCESS	FAILED	Attendee "REPLY" task failed
6	FAILED	FAILED	Overall state set by Organizer for TASK-MODE=CLIENT or by server for AUTOMATIC-FAILURE