BPMI.org

[axw-casenove]

Happy new year !

Here is a question about Exclusive Gateway:

What must be the behavior of an Exclusive Gateway when merging incoming sequence flows ?

In BPMN Working Draft (Version 1.0 - May 3, 2004) on page 87 and 89, it is said that each Token that arrives to the gateway will process through the gateway, "without consideration or synchronization of signals that have arrived from other sequence flow".

However, at the end of page 133 of the same document, in the "Sequence Flow Mechanisms" section, an Exclusive Gateway is used to merge two sequence flows (figure 76), and this time it is said:
"In this situation, the Gateway will accept the first Token and immediately pass it on through to the activity. When the second Token arrives, it will be excluded from the remainder of the flow. This means that the Token will not be passed on to the activity, but will be consumed."

So what is the correct behavior ? Should a Token be stopped because some others have already activated the gateway or can it go through the gateway without matter of others ?

[Stephen A White]

You did find an inconsistency in the spec. The basic rule for all Gateways is that they behave the same for both the incoming and outgoing directions. Thus, the text on pages 87 and 89 is incorrect. The text on page 133 is correct. Exclusive Gateways should be exclusive for incoming Tokens as well as outgoing Tokens.
The specification will be updated for version 1.1.