Following our previous discussion on BPMN task types in Camunda BPM, we now turn our attention to the equally crucial concept of events. Events dictate the sequence and flow of a process, marking the beginning, the occurrences during, and the conclusion of activities.
BPMN Events
Events in BPMN are akin to milestones and signals that guide a process’s journey. They define initiation points, checkpoints, and termini of processes, each with specific triggers and implications.
As we will explore the different BPMN events and their uses, it’s helpful to have a visual guide that summarizes these concepts. Below is a table that categorizes the various BPMN events, which can serve as a quick reference when designing or analyzing workflows in Camunda BPM:
Please note that this table is sourced from the comprehensive reference materials provided by Camunda, which you can explore in greater detail at their official BPMN reference page: Camunda BPMN Reference.
The Basics: None Events
Often depicted as a simple circle, the None Event (also referred to as an unspecified or blank event) adapts its meaning based on its context. Whether serving as a start, intermediate, or end event, None Events are unassuming yet crucial. They provide a canvas for adding details as the process evolves, allowing for flexibility and refinement.
The Lifecycle: Start, Intermediate, and End
- Start Events set the stage, initiating the process.
- Intermediate Events are waypoints, denoting occurrences that can either alter the path or serve as a milestone within the process.
- End Events signify a conclusion, marking the completion of the process path.
- For example, in a product development lifecycle, a Start Event might be the initial design approval, various Intermediate Events could represent developmental milestones or review meetings, and the End Event would be the product’s market release.
Reactive and Proactive: Catching and Throwing
- Catching Events are listeners, patiently waiting for a trigger to react. They represent moments where the process awaits an external signal to continue.
- Throwing Events are the doers, actively signaling a status change or an update, thereby influencing the flow directly without waiting.
- Imagine an IT service desk system: a Catching Event waits for a user’s service request to activate a support ticket workflow, while a Throwing Event might notify the user once their issue is resolved.
The Specifics: Timer, Conditional, and Message
- Timer Events are the timekeepers, scheduled to trigger at specific intervals or moments.
- Timer Start Events set the process in motion at pre-defined times, like the opening of a daily batch job.
- Intermediate Timer Catch Events act as pauses, waiting for a moment in time before proceeding, such as a delay before sending a payment reminder. - Conditional Events are the decision-makers, waiting for a particular condition to be met before taking action.
- They often serve as a watchdog within a process, ensuring certain criteria are satisfied before the workflow proceeds, like inventory levels reaching a re-order point before triggering a purchase order. - Message Events are the communicators, dealing with the sending and receiving of messages.
- Message Start Events might initiate a process in response to a customer inquiry.
- Intermediate Message Events could represent a system awaiting confirmation from an external supplier.
The Flexible Pathways: Event-Based Gateways
Going beyond the linear, Event-Based Gateways offer a way to wait for an event to occur and decide the process path dynamically based on which event happens first. They introduce a level of flexibility, allowing the process to react to real-time situations.
Boundary Events
These are the multitaskers, attached to activities and capable of interrupting or allowing the process to continue when certain events are caught.
- Interrupting Boundary Events might cancel a current task if a higher priority issue arises. For example, if a customer cancels an order while it is being processed. The process would stop the current task of processing the order and move on to handle the cancellation.
- Non-Interrupting Boundary Events allow for parallel processes, like logging a customer’s additional complaint or sending a reminder while their original request is still being processed.
The table displays how different BPMN event types (None, Timer, Conditional, Message) are used in process models, specifically as Catching events for starting or during a process, and as Throwing events to signal an end.
It is adapted from a visual capture from the Camunda Academy’s course materials on BPMN events. For a more detailed exploration and official resources, please visit the specific module on Boundary Events at the following URL: Camunda Academy — BPMN Boundary Events.
Wrapping Up
Just as task types define the work to be done, BPMN events orchestrate how and when the work unfolds in a process. They ensure the process responds appropriately to various conditions and milestones.
