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Why is Or-Split (Implicit) is limited only to 2 inwards arcs? [message #3789]

Fri, 05 July 2013 05:45

lucas
Messages: 1
Registered: July 2013

Junior Member

Hi Tony,

Is there any fundamental reason for not being able to use more than 2 inwards arcs Or-Split (Implicit)?

How do I model a workflow, if I have 3 possible paths from one place?

Thanks,
Lucas

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Re: Why is Or-Split (Implicit) is limited only to 2 inwards arcs? [message #3792 is a reply to message #3789]

Sun, 07 July 2013 04:07

AJM
Messages: 2390
Registered: April 2006
Location: Surrey, UK

Senior Member

There can only be two arcs on an Implicit OR split as one of the transitions must be on a timer. If the other transition does not fire within the time limit then the timed transition will fire.

If you want more than two arcs then you must use an Explicit OR split.

Please refer to Splitting and Joining within a Petri Net

Tony Marston
http://www.tonymarston.net
http://www.radicore.org

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Re: Why is Or-Split (Implicit) is limited only to 2 inwards arcs? [message #5932 is a reply to message #3792]

Tue, 04 October 2016 15:00

kong
Messages: 90
Registered: December 2011

Member

I would like to learn more about the reason for such a limitation in Implicit Or split.
Is this a rule inherent in Petri Net based workflows, or is it to keep the implementation simple, or some other reasons?

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Re: Why is Or-Split (Implicit) is limited only to 2 inwards arcs? [message #5935 is a reply to message #5932]

Wed, 05 October 2016 04:14

AJM
Messages: 2390
Registered: April 2006
Location: Surrey, UK

Senior Member

This is a rule for Petri Nets. Take a look at http://www.project-open.com/en/workflow-petri-nets

Tony Marston
http://www.tonymarston.net
http://www.radicore.org

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Re: Why is Or-Split (Implicit) is limited only to 2 inwards arcs? [message #5940 is a reply to message #5935]

Wed, 05 October 2016 12:43

kong
Messages: 90
Registered: December 2011

Member

Thanks for the link.

After reviewing the information and some further digging, I have the impression these constraints put on the Implicit Or split (namely: 1. The number of arcs coming out must be two and 2. One of the outgoing arcs must go to a Timed Fired transition.) are more of a design decision that the folks at project-open made for their implementation of workflow engine rather than hard Petri Net rules.

Found a nice reference website http://www.workflowpatterns.com/ by the professors who did a lot of the research on this topic. The Implicit-Or Split is referred to as Deferred Choice http://www.workflowpatterns.com/patterns/control/state/wcp16.php and described as follows:Quote:

A point in a process where one of several branches is chosen based on interaction with the operating environment. Prior to the decision, all branches represent possible future courses of execution. The decision is made by initiating the first task in one of the branches i.e. there is no explicit choice but rather a race between different branches. After the decision is made, execution alternatives in branches other than the one selected are withdrawn.

It even gives this exampleQuote:

Once a customer requests an airbag shipment, it is either picked up by the postman or a courier driver depending on who can visit the customer site first.

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Re: Why is Or-Split (Implicit) is limited only to 2 inwards arcs? [message #5944 is a reply to message #5940]

Wed, 05 October 2016 18:25

AJM
Messages: 2390
Registered: April 2006
Location: Surrey, UK

Senior Member

There are two kinds of split in a Petri Net - and Explicit OR split and an Implicit OR split. The Implicit OR split MUST have only two arcs, and one of them must be triggered by a timer. If you don't want a timer then your only alternative is an Explicit OR split.

Tony Marston
http://www.tonymarston.net
http://www.radicore.org

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Re: Why is Or-Split (Implicit) is limited only to 2 inwards arcs? [message #5959 is a reply to message #5944]

Sat, 08 October 2016 07:02

AJM
Messages: 2390
Registered: April 2006
Location: Surrey, UK

Senior Member

I have removed the limitation of only two arcs on an Implicit-OR-splt. See http://radicore.org/fud/index.php?t=msg&goto=5952&#m sg_5952 for details.

Tony Marston
http://www.tonymarston.net
http://www.radicore.org

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