Pm4py - analyze what BPMN can be converted into process tree

background

Read manually drawn BPMN chart , Want to convert it into Process Tree, It must be converted into WF-net.
However, there are irregularities or differences in logic BPMN Cannot be converted to a unique WF-net, It can't be converted into Process Tree.
Process Tree： Process tree , abbreviation PT;
WF-net： Workflow net ,workflow-net, abbreviation WF-net（ yes Petri net A kind of subnet ）;

Problems encountered （ One ）

As shown in the figure above , Say what you give Petri net Is not a WF-net. In fact, normal will not cause this error report , Later it was found that BPMN The annotation of the drawing is wrong , The end of the event is marked as an intermediate event , So draw a BPMN At least be careful , And it's best to conform to the well structured arrangement BPMN. May refer to BPMN - How to draw the basis of good structure arrangement BPMN？

Problems encountered （ Two ）

As shown in the figure above , say WF-net Parse failure . Tracing to the source , Click the error reporting line to locate the error reporting source code .

You can see that the cause of this error is len(grouped_net.transitions) It's not equal to 1.
Let's take a look at this grouped_net What is it , Locate above group_blocks_in_net function .

In fact, it's from the right petri net Make a deal . Return to the processed petri net, So this grouped_net That's what happened petri net.
So this grouped_net Of transitions What is it? , Let's print out this code , Print out the relevant information .
The following reads an error reporting that the above conversion failed BPMN.

bpmn_graph = pm4py.read_bpmn('D:\\PM data \\diagram (10).bpmn')
bpmn_graph = layouter.apply(bpmn_graph)
net, im, fm = bpmn_converter.apply(bpmn_graph)
print(net)
print()
grouped_net = tpt.group_blocks_in_net(net, parameters={
    })
print(grouped_net.transitions)
print(len(grouped_net.transitions))

The first three lines have not been processed petri net Properties of
The penultimate line is processed transitions attribute
The last line is the number of attributes , That is, the front is not equal to 1 The value of
Why is it equal to 1 Well ？ I put the above wrong BPMN Replace it with one that can be converted successfully BPMN

Yes , His number is 1. If you look closely, it really has only one tuple , The first parameter inside is the label , The second parameter is a string .
Take a closer look at his string , In fact, it is a PT Structure , It turns out that it is through this long string to convert into PT Of .

That's why he len(grouped_net.transitions) It's not equal to 1, You can't put untreated petri net convert to PT Why .
Because of this BPMN Logical differences or other reasons , So that he can't merge into 1 A complete process .
These are the analysis process .

The phenomenon ：
The above is wrong BPMN in , I want to draw it as a PT There will be logical differences , I can't draw it at all . Because it is found that the cycle will lead to the conversion into coincidence PT Can't express when .

Possible causes ：
BPMN Of XOR The gateway appears nested , Logical confusion and disagreement .

Conclusion ：
Avoid nested gateways . After a gateway forks out , To merge back .

matters needing attention ：

1. Try to avoid gateway nesting （ Take the cycle , In this cycle , It's best to be wrapped by two gateways , Don't stretch a line out of the loop at a node in the loop , That is, don't create complications ）, You can refer to the cycle in the figure below .
   
   It can be converted into PT,reinitiate request Is the event that triggers the loop .
   
2. Painted BPMN Of XOR Branching and merging can best be seen as two branches , The last two branches merge .
   As shown in the figure below , gateway 1, You can think of the whole block above as an event , In this way, it can be regarded as the bifurcation of two events , Finally, merge the two events with the merge gateway . In fact, this is also to avoid nesting .
   

* If you have questions about this article （ for example ： Incorrect knowledge points or expressions in the notes ）, Welcome to point out , Learn together and make progress .