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Home » RADICORE development » Workflow » Why is Or-Split (Implicit) is limited only to 2 inwards arcs?
Why is Or-Split (Implicit) is limited only to 2 inwards arcs? [message #3789] Fri, 05 July 2013 05:45 Go to next message
lucas is currently offline  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
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 Go to previous messageGo to next message
AJM is currently offline  AJM
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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


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 Go to previous messageGo to next message
kong is currently offline  kong
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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?
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 Go to previous messageGo to next message
AJM is currently offline  AJM
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This is a rule for Petri Nets. Take a look at http://www.project-open.com/en/workflow-petri-nets

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 Go to previous messageGo to next message
kong is currently offline  kong
Messages: 90
Registered: December 2011
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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.
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 Go to previous messageGo to next message
AJM is currently offline  AJM
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Registered: April 2006
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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.

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 Go to previous message
AJM is currently offline  AJM
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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.

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