Executing BPMN 2.0
Workflows in Python
Matt Hampton
PYCONZA 2012
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Outline
• A Tale of Woe
• Business Process Model and Notation
• SpiffWorkflow
o And the Workflow Patterns initiative
• SpiffWorkflow + BPMN
• Recommended Use Case
•Q&A
2
Outline
• A Tale of Woe
• Business Process Model and Notation
• SpiffWorkflow
o And the Workflow Patterns initiative
• SpiffWorkflow + BPMN
• Recommended Use Case
•Q&A
3
But First - Some Context
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Permit to Work
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j5 Interface
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j5 Interface
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The Flow Chart
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Completing a Permit
Version 2
Version 1
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def get_close_button_rights(self):
"""Whether or not the user has the right to click the Close (Isolations Removed) button"""
if self.status in ('Complete','Reactivated','Closed (Isolations Maintained)'):
session = RequestStack.request_stack.session
if session:
if self.approved_by == session.user:
permit_work_table = Alchemy.find_recordclass("permit_work")
with Alchemy.closing(self.session_class()) as sa_session:
associated_permits = sa_session.query(permit_work_table).filter(sqlalchemy.and_(permit_wor
if self.master_permit == 'Yes':
if not associated_permits and (self.num_isolation_points in (0, '0') or self.points_de
if self.gs_required == u"Yes":
if self.gs_test_due == u"False" or self.gs_button_clicked == "Yes":
return 'True'
else:
return 'True'
elif (not self.num_isolation_points in (0, '0') or associated_permits) and self.check_
if self.gs_required == u"Yes":
if self.gs_test_due == u"False" or self.gs_button_clicked == "Yes":
return 'True'
else:
return 'True'
elif (self.points_deisolated == 'True' or self.category in ("Vehicle", "Lifting")):
if self.gs_required == u"Yes":
if self.gs_test_due == u"False" or self.gs_button_clicked == "Yes":
return 'True'
else:
return 'True'
elif self.status == 'Incomplete':
#If the status is Incomplete this button is a Reissue button
session = RequestStack.request_stack.session
if session:
if self.approved_by == session.user:
return 'True'
return 'False'
close_button_rights = property(get_close_button_rights)
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Gratuitous Gang of Four Quote
• Use the State pattern if:
o Operations have large, multipart conditional
statements that depend on the object’s state. The
state is usually represented by one or more
enumerated constants. Often, several operations
will contain this same conditional structure.
o Hmmm.
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Why not State Pattern?
Version 3
Hmmmm….
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OMG!
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OMG!
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OMG(!) BPMN
• Object Management Group
• Business Process Modelling Notation (v1)
o Business Friendly notation in wide use
o Unambiguous semantics
o Clear analysis / communication of requirements
o Asking the right questions
• Business Process Model and Notation (v2)
o Executable Process Definitions
o http://www.bpmn.org
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Start
Event
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User
Task
Script
Task
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Pool
Lane
Lane
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Exclusive
Gateway
(Diverging)
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Parallel
Gateway
(Diverging)
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Intermediate
Catching Event
(Timer)
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Call
Activity
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Boundary Event
(Non-interrupting)
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End Event
(Terminating)
End Event
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Annotations
for Clarity
Facilitates Top-Down
Decomposition of
Complex Processes
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Other BPMN Features
• Exception Handling
• Compensation
• Data Objects
• Multiple Instances / Looping
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Outline
• A Tale of Woe
• Business Process Model and Notation
• SpiffWorkflow
o And the Workflow Patterns initiative
• SpiffWorkflow + BPMN
• Recommended Use Case
•Q&A
29
SpiffWorkflow
• Pure Python Library
• Based on the Worklow Patterns initiative
o http://www.workflowpatterns.com
• Build a ‘Workflow Spec’
• Create a ‘Workflow’ instance
• API for getting a list of READY / WAITING tasks
o Completing a task, moves the workflow forward
• Maintained by Samuel Abels
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class MyWorkflowSpec(WorkflowSpec):
def __init__(self):
WorkflowSpec.__init__(self)
# Build one branch.
a1 = Simple(self, 'task_a1')
self.start.connect(a1)
a2 = Simple(self, 'task_a2')
a1.connect(a2)
# Build another branch.
b1 = Simple(self, 'task_b1')
self.start.connect(b1)
b2 = Simple(self, 'task_b2')
b1.connect(b2)
# Merge both branches (synchronized).
synch_1 = Join(self, 'synch_1')
a2.connect(synch_1)
b2.connect(synch_1)
# If-condition:
excl_choice_1 = ExclusiveChoice(self, 'excl_choice_1')
synch_1.connect(excl_choice_1)
c1 = Simple(self, 'task_c1')
excl_choice_1.connect(c1)
c2 = Simple(self, 'task_c2')
cond = Equal(Attrib('test_attribute1'), Attrib('test_attribute2'))
excl_choice_1.connect_if(cond, c2)
c3 = Simple(self, 'task_c3')
excl_choice_1.connect_if(cond, c3)
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Control Flow Features
• Sequence
• Parallel Split
• Exclusive Choice
• Simple Merge
• Multi-Choice
• Structured Synchronizing Merge
• …..
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Outline
• A Tale of Woe
• Business Process Model and Notation
• SpiffWorkflow
o And the Workflow Patterns initiative
• SpiffWorkflow + BPMN
• Recommended Use Case
•Q&A
33
SpiffWorkflow + BPMN
• Pluggable Parser
• Extensible Task Spec classes
o Allows the use of BPMN extension elements
• Pluggable Script Engine
o Executes script tasks
o Evaluates expressions
• Database-friendly Workflow Serialization
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Supported BPMN Features
• Call Activity
• Start Event
• End Event (including interrupting)
• User and Manual Tasks
• Script Task
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Supported BPMN Features
• Exclusive Gateway
• Parallel Gateway
• Intermediate Catch Events (Timer and
Message)
• Boundary Events (Timer and Message,
interrupting and non-interrupting)
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Eclipse BPMN2 Modeler
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Gemsbok (ex-Signavio)
Custom
‘Stencil Set’
Custom
Properties
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Project Status
• BPMN extension is currently in a fork:
o https://github.com/matthewhampton/SpiffWorkflow
o Should be merged in to the base project in the
next month
• Gemsbok is here:
o https://github.com/matthewhampton/Gemsbok
• Eclipse BPMN2 Modeler is here:
o http://eclipse.org/bpmn2-modeler
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Outline
• A Tale of Woe
• Business Process Model and Notation
• SpiffWorkflow
o And the Workflow Patterns initiative
• SpiffWorkflow + BPMN
• Recommended Use Case
•Q&A
45
Is BPMN for you?
• Small number of states?
o Use the State Pattern, or a similar OO
decomposition
• Single-threaded & No Actions on Transitions
o Table-based State Machine
• Complex workflows?
• Getting tied up in specification round trips?
• Like Pretty Pictures?
OMG BPMN!
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Outline
• A Tale of Woe
• Business Process Model and Notation
• SpiffWorkflow
o And the Workflow Patterns initiative
• SpiffWorkflow + BPMN
• Recommended Use Case
•Q&A
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