I'm new to Pega and had my problems with that differentiation as well. As my predecessor said a step is a process - so the actual action taking place. Whereas a stage is a grouping of steps that belong together.
Here are two ways to group those steps as I see it. They can be identified with the same abstract category (e.g.: in the process of applying for a visa collecting all necessary documents would be part of the preparation stage). This can especially also inculde that the stages indicate a transfer of the responsibility from one person to another person.
There is no definite rule to define as when to create a Stage and Step. It all depends on the requirement and how the lifecycle of the workitem progress or the optimal design of the requirement.
It all depends on how the workitem will be handled and completed. Say, for example you order an item in online Store, look at the details of the order as how it progressed
It has various stages like:
Place order, Approval, Processing, Shipping, Delivery, Feedback
And Steps can be added under each stage as below:
Place Order: Select Product, Enter Shipping Address, Confirm
Approval: Automatic Approval, Inventory Approval
Processing: Get the ordered item, Quality Check, Package Creation
Shipping: Ship to Local store, Ship to Customer
Delivery: Item received, Customer Unavailable to deliver
Feedback: Provide Feedback
The above is a sample of how you define the stage and steps. You can refine them based on your requirement.
Say, Approval can be redefined as two stages:
Automatic Approval and Inventory Approval where the first stage is automatically progressed based on the stock available in the Inventory. If Stock is not available, then the order will be cancelled. If the stock is available, then Inventory Approval is needed.
You can skip the stages when certain conditions are met. All such processes are based on how you deal with the given requirement to meet its business needs.
Just keep below things in mind and you won't be in dilema.
1. Case Type--- Business Process.
2. Stage--- Milestone in a given business process.
3. Step--- combination of actions/tasks to achieve a milestone.
Consider a very trivial real world ER app ex.--> Payment Investigations (SI).
An enquiry mssg arrives (SWIFT). The same needs to be parsed, followed by detection whether its a new message or a response to an existing enquiry (if follow-up then attached to existing enquiry case), thereafter the payment reference is located from the parsed message (transaction reference) by hitting payment hub SOR, finally a new enquiry case is created to carry out payment investigation.
Few pointers from the above lines. Clearly it depicts 2 case types (enquiry msg/enquiry case). For enquiry msg case the stages n steps would be following:
Enquiry Msg Parsing-->This includes determining different type of swifts, parsing their swift body. And many other FR specific details.
Determine Enquiry Msg Nature (new or follow-up)-->This includes locating an existing enquiry case by case ref or transaction ref (from the incoming parsed msg). Further if found, then attaching to existing case (creating any review assignment) or if case found locked then queuing for retrial.
Transaction Search-->Locating different type of transactions like USD, Bourn, Frank, their related messages. This is very specific to the payment domains, to summarize its a big milestone and hence categorized as a stage.
Enquiry Case Creation--> This includes new enquiry case creation (in case of a new msg).
And now finally, i believe you can guess that whatever tasks that every stage is mentioned to achieve will become the STEPS for that corresponding stage.