Issue 14815: Link Events - Constraints and Usage not clearly documented (bpmn2-rtf)
Source: International Business Machines (Ms. Suzette Samoojh, ssamoojh(at)ca.ibm.com)
Nature: Clarification
Severity: Minor
Summary: The Sequence Flow constraints around the usage of Link Events are not clearly expressed in the spec.


Very simply, it should express that:
 - A Catch Link Event should have no incoming Sequence Flow.
 - A Throw Link Event should have no outgoing Sequence Flow.


Instead the spec has several rather confusing statements (pgs 235-236) that make it hard to infer the simple behavior I described above.
Statements like:
- If the Intermediate Event is used within normal flow:
   - Intermediate Events MUST be the target of a Sequence Flow.
- An Intermediate Event MUST be a source for Sequence Flow.
   - An exception to this: a source Link Intermediate Event (as defined below), it is not required to have an outgoing Sequence Flow.
- A Link Intermediate Event MUST NOT be both a target and a source of a Sequence Flow.  
- A Link Intermediate Event MAY be the target (target Link) or a source (source Link) of a Sequence Flow, but MUST NOT be both a target and a source.


Recommendation:
 - Tighten up and simplify the constraint descriptions for Link Events.
 - Refrain from introducing new terms "source" and "target", or if the new terms are needed, clearly relate them to the existing "catch" and "throw" terms.
Resolution: 
Revised Text: 
Actions taken:
November 23, 2009: received issue
Discussion: 
The FTF agrees that there is a problem that needs fixing, but did not agree on a resolution and deferred its resolution to a future RTF/FTF.
Disposition: Deferred
End of Annotations:=====

m: webmaster@omg.org
Date: 23 Nov 2009 17:46:55 -0500
To: <issues@omg.org>
Subject: Issue/Bug Report


*******************************************************************************
Name:          Suzette Samoojh
Company:       IBM Canada
mailFrom:      ssamoojh@ca.ibm.com
Notification:  No
Specification: BPMN 2.0
Section:       10.4.4
FormalNumber:  dtc/2009-08-14
Version:       2.0
RevisionDate:  08/14/2009
Page:          235-236
Title:         Link Events - Constraints and Usage not clearly documented
Nature:        Clarification
Severity:      Minor
test:          3qw8
B1:            Report Issue


Description:


The Sequence Flow constraints around the usage of Link Events are not clearly expressed in the spec.


Very simply, it should express that:
 - A Catch Link Event should have no incoming Sequence Flow.
 - A Throw Link Event should have no outgoing Sequence Flow.


Instead the spec has several rather confusing statements (pgs 235-236) that make it hard to infer the simple behavior I described above.
Statements like:
- If the Intermediate Event is used within normal flow:
   - Intermediate Events MUST be the target of a Sequence Flow.
- An Intermediate Event MUST be a source for Sequence Flow.
   - An exception to this: a source Link Intermediate Event (as defined below), it is not required to have an outgoing Sequence Flow.
- A Link Intermediate Event MUST NOT be both a target and a source of a Sequence Flow.  
- A Link Intermediate Event MAY be the target (target Link) or a source (source Link) of a Sequence Flow, but MUST NOT be both a target and a source.


Recommendation:
 - Tighten up and simplify the constraint descriptions for Link Events.
 - Refrain from introducing new terms "source" and "target", or if the new terms are needed, clearly relate them to the existing "catch" and "throw" terms.