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iCal4j Actions - Workflow

A workflow automation library using iCalendar to define workflow definitions and state.

Overview

A typical workflow system supports the creation of workflow rules that control how tasks are generated and fulfilled.

The iCal4j Actions Workflow Engine builds on the streams framework with support for configurable workflows defined as iCalendar actions.

Time-based workflows

Such workflow definitions can be expressed as time-based recurring actions:

BEGIN:VCALENDAR
BEGIN:VTODO
DTSTART:20250101T080000
DURATION:PT1H
SUMMARY:Turn on the lights
RRULE:FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR
END:VTODO
END:VCALENDAR

The workflow engine will generate a list of occurrences from this definition (for a specific period of time) to schedule tasks:

BEGIN:VCALENDAR
BEGIN:VTODO
DTSTART:20250101T080000
DURATION:PT1H
SUMMARY:Turn on the lights
RRULE:FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR
RECURRENCE-ID:20250101T080000
STATUS:NEEDS-ACTION
LAST-MODIFIED:20241231T210000Z
END:VTODO
END:VCALENDAR

A task executor may specifically check for tasks that it can complete, and update the status accordingly:

BEGIN:VCALENDAR
BEGIN:VTODO
DTSTART:20250101T080000
DURATION:PT1H
SUMMARY:Turn on the lights
RRULE:FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR
RECURRENCE-ID:20250101T080000
STATUS:IN-PROCESS
ATTENDEE:mailto:[email protected]
LAST-MODIFIED:20250101T080130Z
END:VTODO
END:VCALENDAR

Note that the "task executor" may be a human or an automated system

Once completed the task can be marked as such:

BEGIN:VCALENDAR
BEGIN:VTODO
DTSTART:20250101T080000
DURATION:PT1H
SUMMARY:Turn on the lights
RRULE:FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR
RECURRENCE-ID:20250101T080000
STATUS:COMPLETED
ATTENDEE:mailto:[email protected]
LAST-MODIFIED:20250101T080500Z
COMPLETED:20250101T080500Z
END:VTODO
END:VCALENDAR

If a task is not fulfilled in the required timeframe a dedicated task reaper can close it automatically:

BEGIN:VCALENDAR
BEGIN:VTODO
DTSTART:20250101T080000
DURATION:PT1H
RECURRENCE-ID:20250101T080000
STATUS:CANCELLED
SUMMARY:Turn on the lights
RRULE:FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR
LAST-MODIFIED:20250101T090100Z
END:VTODO
END:VCALENDAR

This approach to workflows fulfills the following necessary features:

  • Workflow tasks are durable, in that if the workflow system has an outage the currently active tasks are preserved.
  • State of tasks is also tracked and durable.
  • Timers are implicitly defined in the workflow definition such that incomplete tasks are automatically expired.

Other workflow triggers

Some workflows may not define a recurring time component, in which case they would only be triggered by some condition:

BEGIN:VCALENDAR
BEGIN:VTODO
DTSTART:20250101T080000
DURATION:PT1D
SUMMARY:Approve funding request
UID:9999
END:VTODO
END:VCALENDAR

For such workflows the engine would recognise the conditions required to generate a new task:

BEGIN:VCALENDAR
BEGIN:VTODO
DTSTART:20250101T080000
DURATION:PT1D
SUMMARY:Approve funding request
RELATED;RELTYPE=PARENT;VALUE=UID:9999
RELATED;VALUE=UID:1234
STATUS:NEEDS-ACTION
LAST-MODIFIED:20241231T210000Z
END:VTODO
END:VCALENDAR