BPMN21 — Exclusive gateway Choreography rules too restrictive, only sender needed

Decisions are prevented from being used Choreographies if not all
participants have access to the information on which the decision is
made. But if the activities following the gateway are all sent by the
same participant, only that participant needs to know how the decision
is made. Using an event-based gateway in this case is confusing, since
there is no waiting for events to proceed to the activities following
it. Some sided email below about this.

Steve,

> The Gateway would most likely be Event based. The Buyer is
> probably not going to be aware of the data that would be
> used to make the decision, particularly a change order.
> Thus, the Buyer is just going to be waiting for one of the
> three responses.

Makes sense for the buyer, but this isn't a model of the buyer (and the
Seller is making a regular decision, why isn't that shown?).

It's also odd to see an event-based gateway in a choreography since
choreography can't don't wait for events, the participants do. The
figure looks right according to the spec, but I think the spec is too
restrictive on regular decisions in choreogrpahies.

Conrad

Steve,

> The Seller is making a regular decision internally, but the
> rationale (i.e., data) used to make the decision is private
> for the Seller. A Choreography can only use Exclusive
> Gateways if the data used for them is public.

I understand that's the rule, but I'm not sure it make sense. In this
case, the activities following the gateway are all initiated by the
Seller. The rule should be that the seller has access to the decision
data.

> The Buyer does not know ahead of time, what the
> results of the decision will be since the Buyer has not seen the
> Seller's internal data.

And that's fine, because it isn't the Buyer who initiates any of the
activities after the gateway.

> All private Exclusive Gateways show up as Event Gateways in a
> Choreography.

This is too hard to explain, for example, who receives the event? The
choreography itself can't received an event, and there's no indication
that it's the Buyer (other than they Buyer is receiving in the
activities after the gateway).

For FTF discussion.

Conrad