ebBP 12/8/2005: BPMN Diagram Update and Question on Gateways

[Monica J Martin <Monica.Martin@Sun.COM>]

As we discussed in Tuesday's call, the team is to review the BPMN 
updated diagrams for inclusion in v2.0.1 pre-Committee Specification. At 
a minimum, one possible open question exists regarding the appropriate 
use of the exclusive or inclusive OR gateway notation object. We 
discussed this briefly 15 November 2005 [1]. At that time, Dale Moberg 
asked why we had been asked to use an inclusive OR notation object 
rather than an exclusive OR. With inclusive OR, parallelism could 
result. For example, in a decision, it is modeled that one path is 
taken. The challenge lies in that BPMN v1.0 doesn't support message 
flows into/out of a gateway. In order to represent the sequence flow 
into a gateway, and several possible paths out (termed intermediate 
messages in BPMN), I opted to use the inclusive OR gateway at the 
suggestion of the BPMN team.

In ebBP, forks can be non-deterministic intentionally. Forks can 
resemble a non-deterministic OR or parallel ANDs or exclusive OR (like a 
Decision). We should consider what options we have (if the updated 
diagrams don't fit) to represent this appropriately. We could also 
choose to annotate the diagram for more clarity. I encourage everyone to 
look at the updated diagrams referenced in the 21 November 2005 post and 
comment (particularly you Dale).

I've also cc: Stephen White and Ugo Corda so they are aware of the 
conversations, and can comment if need be from a BPMN perspective. Thanks.

[1] 
http://www.oasis-open.org/apps/org/workgroup/ebxml-bp/document.php?document_id=15516 
(Meeting Minutes, 15 November 2005)

Note: We've had some mail server issues recently and messages are being 
dropped. I posted this on Tuesday but it never showed up however. Sorry 
for any duplication or confusion. If I don't respond to a particular 
message please resend it. I may have not received it in the first place. 
Thanks.

=================
Email references:
28 November 2005: A reminder that the TC team is to review these 
questions and the updated diagrams, particularly the questions regarding 
exclusive and inclusive/or gateways. We will discuss 29 November 2005. 
Please post your questions if possible before Tuesday's meeting. Thanks.

Reference: 
http://www.oasis-open.org/apps/org/workgroup/ebxml-bp/email/archives/200511/msg00050.html

> 21 November 2005: As we discussed in Tuesday's call last week, the 
> team wished to review in more detail the BPMN v1.0 and draft v1.1 
> specification, and the diagrams as updated. As previously indicated, I 
> had worked with Ugo Corda to determine if and how using BPMN we can 
> show how ebBP can map the Business Transaction Activity to a series of 
> operations (OperationMapping). What is important here and perhaps 
> should be considered by BPMN team is there is effectively no mechanism 
> to specify a relationship between activity objects unless they are 
> considered a subprocess or a transaction or within a pool/lane. 
> Neither of these truly represent this use case. There are (at least) 
> two levels of specification where we should be able to associate or 
> relate the BTA to those operations, each effectively activities in 
> their own right. There are some other points to consider regarding 
> differentiating signals from business messages, how to accurately show 
> an operation, and what objects/lines to use to show responses vs. faults.
>
> Here is a summary of the discussion and potential items to address:
>
> * Question 1: How to map complex activities to a series of
> operations, where these operations may be associated with or
> related to a BTA? When you choose this particular mapping are you
> in essence combining different process diagrams in the BPMN
> vernacular?
>
> * It is not an embedded subprocess
>
> "....An Embedded (or nested) Sub-Process object is an activity
> that contains other activities (a Process). The Process within
> the Process is dependent on the parent Process for instigation
> and has visibility to the parent’s global data. No mapping of
> data is required. The objects within the Embedded Sub-Process,
> being dependent on their parent, do not have all the features of
> a full Business Process Diagram, such as Pools and Lanes. Thus,
> an expanded view of the Embedded Sub-Process would only contain
> Flow Objects, Connecting Objects, and Artifacts....
>
> * It is not a group (relatively speaking), although it shares
> some characteristics of a group.
>
> "...A box around a group of objects for documentation
> purposes)....A grouping of activities that does not affect the
> Sequence Flow. The grouping may be used for documentation or
> analytic purposes. Groups can also be used to identify
> activities of a distributed transaction that is shown across Pools."
>
> * It is not an association (dotted line) although we can
> relate or associate the abstract WSDL operations to BTA
> (Note that the operation is not an artifact, it is in
> essence another flow object).
>
> "...To satisfy additional modeling concepts that are not part of
> the basic set of flow elements, BPMN provides the concept of
> Artifacts that can be linked to the existing Flow Objects
> through Associations. Thus, Artifacts do not affect the basic
> Sequence or Message Flow, nor do they affect mappings to
> execution languages....An Association is used to associate
> information with Flow Objects. Text and graphical non-Flow
> Objects can be associated with the Flow Objects...."
>
> * Question 2: What gateway control type is appropriate when you
> actually could have -n- potential paths on a fork or join, and
> either only one is actually performed or many could be performed,
> and business messages are sent? This is actually a conceptual
> difference in current BPMN v1.0 and collaboration whereby not all
> paths may be rendered executable or be used in execution
> (monitorable in ebBP context).
> o The BPMN team had questioned why we used an exclusive/or
> rather than inclusive/or gateway (See Section 3.2 objects)
> when we could have multiple input or output from a fork or
> join. This is represented in a gateway in BPMN. The
> inclusive/or gateway with the message flow is not allowed in
> BPMN.
> o The BPMN team had questioned why we needed to have multiple
> messages as input to or output from a gateway (which is not
> allowed in BPMN).
>
> Instead of using an exclusive/or gateway with multiple message
> flows into or out of an exclusive/or gateway, I updated the
> diagrams to show an inclusive/or with sequence flows to
> intermediate messages to show that one actual Response on the
> Responding Business Activity results. See v2.0.1 CD and v2.0.1
> PR diagram changes to visually represent this discussion. Please
> also review BPMN Section 4.5 that talks about exclusive/or
> gateway and how condition expressions are used (XPath based for
> example) to effect what path(s) is/are taken. It appears that an
> exclusive/or gateway could be used but the assumptions are
> different (shows sequence rather than the potential flow of
> business messages which may suit our needs).
>
> * Question 3: Differentiating business messages and/or business
> signals: As allowable extensions, I have differentiated business
> messages from business signals (blue and green respectively for
> color, and used a heavier weight line). The BPMN team may consider
> that this differentiation is important for intentional collaboration.
> * Question 4 (related to Question 1) : When you have a complex
> activity that may be mapped multiple operations, how do you
> represent the fact that an abstract WSDL operation could have the
> Response or a fault(s)? See our updated Figure 8.
>
> Diagrams I've included:
>
> 1. Diagrams as specified in v2.0.1 Committee Draft (2 diagrams)
> * Requesting and Responding Business Activity on a typical
> Commercial Transaction pattern.
> * Requesting and Responding Business Activity on a typical
> Commercial Transaction pattern using Operation Mapping.
> 2. Diagrams updated given comments from BPMN team for v2.0.1 Public
> Review draft candidate (2 diagrams)
> * Requesting and Responding Business Activity on a typical
> Commercial Transaction pattern.
> * Requesting and Responding Business Activity on a typical
> Commercial Transaction pattern using Operation Mapping.
>
> Relevant references:
>
> * Updated ebBP diagrams -
> http://www.oasis-open.org/apps/org/workgroup/ebxml-bp/email/archives/200511/msg00035.html 
>
> (14 November 2005)
> o All diagrams uploaded to ebBP site for ease of accessibility:
> + (TC)
> http://www.oasis-open.org/apps/org/workgroup/ebxml-bp/document.php?document_id=15368 
>
> + (public)
> http://www.oasis-open.org/committees/document.php?document_id=15368&wg_abbrev=ebxml-bp 
>
>
> Note. The file (.zzz) needs to be renamed to a (.zip) to
> open and view the four diagrams.
>
> * BPMN v1.0:
> http://www.bpmn.org/Documents/BPMN%20V1-0%20May%203%202004.pdf
> * BPMN v1.1 (draft): http://www.bpmn.org/Documents/BPMN%201-X.pdf
>
> Finally, Stephen and Ugo, I'd like to log these as questions to the 
> BPMN team for future consideration as appropriate. Thanks.