BPMN21 — Message Flow Connections for Start, End and Intermediate Events

i) Chapter/Section 10.4.2. Page 253. Message Flow Connections for Start Events
It says:

• A Start Event MAY be the target for a Message Flow; it can have zero (0) or more incoming Message Flows. Each Message Flow targeting a Start Event represents an instantiation mechanism (a trigger) for the Process. Only one of the triggers is REQUIRED to start a new Process.

• A Start Event MUST NOT be a source for a Message Flow; it MUST NOT have outgoing Message Flows.

ii) Chapter/Section 10.4.3. Page 257. Message Flow Connections for End Events
It says:

• An End Event MUST NOT be the target of a Message Flow; it can have no incoming Message Flows..

• An End Event MAY be the source of a Message Flow; it can have zero (0) or more outgoing Message Flows. Each Message Flow leaving the End Event will have a Message sent when the Event is triggered.

• The Result attribute of the End Event MUST be set to Message or Multiple if there are any outgoing Message Flows.

• The Result attribute of the End Event MUST be set to Multiple if there is more than one (1) outgoing Message Flows

iii) Chapter/Section 10.4.4. Page 268. Message Flow Connections for Intermediate Events
It says:

• A Message Intermediate Event MAY be the target for a Message Flow; it can have one (1) incoming Message Flow.
• A Message Intermediate Event MAY be a source for a Message Flow; it can have one (1) outgoing Message Flow.
• A Message Intermediate Event MAY have an incoming Message Flow or an outgoing Message Flow, but not both.

COMMENTS:

In it is not explained when the Start Event can have incoming Message Flows.
The rules are:
The Start Event MUST be associated with one (1) or more MessageEventDefinitions if there are any incoming Message Flows.
The Start Event will be Message, Multiple or Parallel Multiple if there are any incoming Message Flows.
The Start Event will be Multiple or Parallel Multiple if there is more than one (1) incoming Message Flows.

In it is said “Only one of the triggers is REQUIRED to start a new Process”, this is true for a Multiple Start Event, but not for a Parallel Multiple Start Event.

In (ii) the “Result” attribute is mentioned. It was an attribute of End Event in BPMN 1.2, but not in BPMN 2.0. (see Figure 10.69, p. 241).
The rules are:
The End Event MUST be associated with one (1) or more MessageEventDefinitions if there are any outgoing Message Flows.
The End Event will be Message or Multiple if there are any outgoing Message Flows.
The End Event will be Multiple if there is more than one (1) outgoing Message Flows.

In (iii) it is described only the Message Intermediate Event, but Multiple and Parallel Multiple Intermediate Events can be the source or the target of Message Flows too.

SUGGESTIONS:

In add the rules that define when the Start Event can have incoming Message Flows, and consider the case when a a Parallel Multiple Start Event is used.

In (ii) remove references to “Result” attribute and update the rules that define when the End Event can have outgoing Message Flows.

In (iii) describe the rules concerning Message Flows for Multiple and Parallel Multiple Intermediate Events.