Organizing More Complex Workflows¶

BPMN Model¶

We’ll be using the following files from spiff-example-cli.

lanes workflow
top_level workflow
call_activity workflow
product_prices DMN table
shipping_costs DMN table

Lanes¶

Lanes are a method in BPMN to distinguish roles for the workflow and who is responsible for which actions. In some cases this will be different business units, and in some cases this will be different individuals - it really depends on the nature of the workflow. Within a BPMN editor, this is done by choosing the ‘Create pool/participant’ option from the toolbar on the left hand side.

We’ll modify our workflow to get the customer’s payment information and send it to an employee who will charge the customer and fulfill the order.

Workflow with lanes

To run this workflow

./run.py -p order_product \
     -d bpmn/product_prices.dmn bpmn/shipping_costs.dmn \
     -b bpmn/lanes.bpmn

For a simple code example of displaying a tasks lane, see Handling Lanes

Subprocesses¶

In general, subprocesses are a way of grouping work into smaller units. This, in theory, will help us to re-use sections of business logic, but it will also allow us to treat groups of work as a unit.

Subprocesses come in two different flavors. In this workflow we see an Expanded Subprocess. Unfortunately, we can’t collapse an expanded subprocess within BPMN.js, so expanded subprocesses are mainly useful for conceptualizing a group of tasks as a unit.

It also possible to refer to external subprocesses via a Call Activity Task. This allows us to ‘call’ a separate workflow in a different file by referencing the ID of the called workflow, which can simplify business logic and make it re-usable.

We’ll expand ‘Fulfill Order’ into sub tasks – retrieving the product and shipping the order – and create an Expanded Subprocess.

We’ll also expand our selection of products, adding several new products and the ability to customize certain products by size and style in addition to color.

Updated Product List

Note

I’ve added what customizations are available for each product in the ‘Annotations’ column of the DMN table. This is not actually used by Spiff; it simply provides the option of documenting the decisions contained in the table.

Since adding gateways for navigating the new options will add a certain amount of clutter to our diagram, we’ll create a separate workflow around selecting and customizing products and refer to that in our main workflow.

Subworkflow for product selection

When configuring the subworkflow, we need to make sure the ‘CallActivity Type’ of the parent workflow is ‘BPMN’ and the ‘Called Element’ matches the ID we assigned in the subworkflow.

Parent workflow

Running the Model¶

./run.py -p order_product \
     -d bpmn/product_prices.dmn bpmn/shipping_costs.dmn \
     -b bpmn/top_level.bpmn bpmn/call_activity.bpmn

Example Application Code¶

Handling Lanes¶

We are not required to handle lanes in our application, but most of the time we’ll probably want a way of filtering on lanes and selectively displaying tasks. In our sample application, we’ll simply display which lane a task belongs to.

if hasattr(task.task_spec, 'lane') and task.task_spec.lane is not None:
    lane = f'[{task.task_spec.lane}]'
else:
    lane = ''

The tasks lane can be obtained from task.task_spec.lane. Not all tasks will have a lane attribute, so we need to check to make sure it exists before attempting to access it (this is true for many task attributes).

See the Filtering Tasks Section of A More In-Depth Look at Some of SpiffWorkflow’s Features more information about working with lanes in Spiff.