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BPMN is very popular notation for process modeling and it's theory is based on task sequences and work flows between actors. So it's seems that it's necessary condition to declare at least two lane (Actor) for model. But sometimes i find independent processes that only one actor has been engaged. Is it valid to draw such BPM with just one lane?

Shahab_HK
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The purpose of a swimlane diagram is specifically to show the interaction between different functional capacities or organizational roles.

Can BPM be created with just one lane?

The diagram would be valid (as there is no rule against this) though uninteresting (as a swimlane diagram) because it is essentially degenerate.

A swimlane diagram with only one swimlane is probably showing a business process that is either insufficiently decomposed, or not shown in sufficiently rich context.

As far as decomposition, since the point of the swimlane diagram is to show roles and how their responsibilities interact, a swimlane diagram showing just one role (e.g. the whole company) is really not telling us much about who does what.  Chances are pretty good that you can decompose the single swimlane into more detail to identify separate interacting departments in the company.

Regarding context, if there are any inputs or outputs of the process, then actors for these are the other swimlanes, so with them you'll then have two or three swimlanes.  A process without inputs & outputs is arguably lacking in significance.

A one-swimlane diagram is more like a flowchart, which identifies steps and flow, but doesn't identify the roles.  Roles are a relative concept — they are relative to each other, e.g. customer﹘supplier, sender﹘receiver, etc..  So, if you have a role, then almost by definition, you have another role.

That being said, a one swimlane diagram can sometimes be a natural start to a more complete diagram, so, most tooling would allow you to create and save such a diagram.

Erik Eidt
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  • Thank you for your response. I think i'v got your hint. You say if there are some processes which seems to has one swimlane, presumably it's role has to be decompose to various roles in order to show how their responsibilities interact. But What if it's impossible to decompose the role? (continue in next comment) – Shahab_HK Jun 23 '19 at 11:06
  • For example suppose that user want to fill a form and submit it in order to receive some information about something. Maybe one say "System" could consider as a role and it's tasks are receiving user form, analyzing data, and sending information to user. But i think it's not very professional to consider system as a role in BPM. Because the whole of BPM tasks has been occurred in our system and if system declare as a role then tasks must be assigned to system role decussate. Because any action has a response.(...) – Shahab_HK Jun 23 '19 at 11:07
  • So what should be done in these cases? Are these process shorter than to model and must be considered as a part of larger process? – Shahab_HK Jun 23 '19 at 11:07
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    Yes, if decomposing doesn't help you or shifts focus where you don't want it, then add more surrounding context. The System is interacting with a User, so that is at least two swimlanes. As far as naming the roles, consider who the system operates on behalf of. – Erik Eidt Jun 23 '19 at 12:41