Professor Adams' Lecture Materials

Learning Objective M03A-08: Understand and apply flow object types.

The Token Concept

A start event generates a token.
That theoretical token must be able to flow through the process—along every potential path—until it reaches an end event.
Tokens only travel along sequence flows and pass through process flow objects.
Tokens do not traverse message flows.

Flow Object Types

Flow objects include events, activities, and gateways.
Sequence flows only connect to flow objects.
Each flow object can be further characterized by type by adding a type icon to the specific flow object symbol.
For example, a “timer” event would show the event with a clock face icon inside, and a “message” event would show the event with an envelope icon inside.

Gateway Types

Exclusive Gateway

The trip involves either flights or a rental car but not both.

Inclusive Gateway

The trip involve either flights or a rental car or both.

Parallel Gateway

The trip will require reservations for all three: flights, rental car, and hotel accommodations.

Event Types

Message Events Example

The process starts with a start message events that receives (catches) the “Request” message from the external participant. The process proceeds to the “Evaluate Request” task, and then the intermediate message event sends (throws) the “Evaluation” message flow to the external participant. The process flow continues to the next intermediate message event where it waits (the token stops) until the external participant responds with the “Confirm” message flow. When the event catches the message, the sequence flow continues to the “Do Something” task and then the process ends. The end message event throws a message to the external participant that the process is done. (Note that if there is only one lane, you don’t need the pool symbol.)

Timer and Boundary Events

The start timer begins the process two weeks before the birthday to be celebrated. The “Plan Party” task has an intermediate error event attached to its boundary (a boundary event). Specifically, this is an example of an interrupting boundary event that affects process flow when an error occurs in the Plan Party task. If an error occurs, then the process flows to the “Cancel Party” task and then ends. However, if the Plan Party task completes successfully, the process flows to the intermediate timer event and then waits two weeks (the token waits to proceed). After two weeks, the process continues to the “Hold Party” task and then ends.

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