[sixdimensional]

Thank you for adding this flavor to the discussion. I do agree that Petri nets are often seen as too complex for basic business process modelling, which is why languages such as BPEL and BPMN were invented by OMG before, and then simplified into UML activity diagrams, for example.

That is to say, level of complexity in describing process in Petri net "modelling language" might seem higher. I can surely see how it feels more esoteric and not always clear how it ties to the implementation.

Many workflow engines take the approach you're describing, for example, I also used to use Microsoft's Windows Workflow Foundation to do similar things. Essentially you're sketching a workflow process skeleton and then managing the state atomically by compartmentalizing it, so to speak.

Actually, this is exactly what Petri nets propose - state is defined by tokens in places - i.e. compartmentalized.

I don't entirely agree with your comment about state management and argument passing in Petri nets. I do agree it takes digging around to find tangible examples/applications that cover argument passing, but the idea of "tokens in places and how they enable transitions of state" is the part of the puzzle to represent in an abstract way, the tiny pieces of state/arguments that enable transitions to fire. I could represent your code above as transitions which cannot fire until tokens representing the state of your conditions were present in the right places. For example, the passage of time was present in an input place, and the condition trial period = true and value customer ID is not blank, all as tokens that have to be in input places to enable the transitions to fire which trigger those activities.

This is to say that, I agree that representing that graphically using Petri net modelling may not be as business friendly as say, UML activity diagramming. But it also doesn't make the simpler approach any less a subset of what you can do with Petri nets, as it very much is one.

But definitely agree, use the right level of abstraction that fits the need, like the old adage, try to use the right tool for the job.

I'd argue that, the tool you describe could be modeled as a Petri net, but that perhaps you may not wish to have a user do it that way.

Do you agree or have a different opinion?

[mfateev]

> I also used to use Microsoft's Windows Workflow Foundation to do similar things. Essentially you're sketching a workflow process skeleton and then managing the state atomically by compartmentalizing it, so to speak.

temporal.io and Windows Workflow Foundation are completely different. WF uses code to generate an intermediate representation of the workflow AST. And that intermediate representation is executed. It is similar to the most existing workflow engines from Airflow to BMPN ones.

Temporal doesn't use any intermediate representation. It directly executes the code keeping all its state durable.

> I don't entirely agree with your comment about state management and argument passing in Petri nets.

When I say about the state I mean the overall state of the business project which is much more than a token in a certain dish. For example such state can include a list of line items to order with all associated attributes and counters of processed events.

> I'd argue that, the tool you describe could be modeled as a Petri net, but that perhaps you may not wish to have a user do it that way.

All software at the lowest level can be modeled as a state machine. And Petri net is one of the possible representation of FSN. I'm interested in simplifying the way the workflow logic is specified by an engineer. At this point I believe the temporal.io approach of giving your the full power of a high level programming language and taking care of durability and scalability is the best option.

[sixdimensional]

NOTE: I am not associated with temporal.io in any way, just learned about it frankly.

I just had a look through your docs and I understand the approach you're taking... similar to "infrastructure as code" concept applied to simplifying workflow. What you are saying makes sense to me. I haven't heard of temporal.io before (cool, hi!), but I get the concept of trying to eliminate the intermediate representation (which I suppose also could be seen as a bottleneck in a fully distributed system and to the "workflow" of a software engineer).

I would point out that, Petri net is a theory and modelling language for proving correctness/soundness of a model - and as I mentioned earlier, I agree that if you don't need that for your use case, yeah - it could be too much. I would like to make it clear for other readers that Petri nets are not specifically the implementation of a technology, they are a modelling technique/concept which could also be implemented/executable through an engine. Having, or not having, an intermediate representation in compiled code or runtime has nothing to do with whether or not you want to model your FSM, or graph, or network of processes, logic and state as a Petri net.

My goal in originally posting the comment was just to share the superset theory of Petri nets, as I don't often see people bring it up in discussions on workflow, FSM, etc.

The comment that Petri nets are one possible representation of FSM is true, with the key difference being that FSM are for single threaded operations and have some limitations in that regard, whereas Petri nets, as the superset, also handle concurrent operations - and workflow is a common use case where we see concurrent operations (but certainly not the only one, and industrial control, etc. is certainly more complicated that organizational workflow). I think this deck is kind of handy for describing some of the differences between FSM and Petri nets [1]. Interestingly, we know that dealing with concurrency, parallel processing, multithreading is difficult, which is why any tools to reduce some of that complexity from day-to-day coding (ex. coroutines/async/await, workflow engines, etc.) make the engineer's life easier.

When we were talking about compartmentalization/encapsulation of state, I see how conceptually you are abstracting that away from the engineer in temporal. I suppose, what I meant when I was talking about WWF was, the fact that the engineer's code and their own state could be "compartmentalized" into the pluggable definitions of the activities provided by the workflow engine. It seems like your team has kind of inverted that a little bit, but roughly the idea is similar. You appear to have the engineer "write the workflow as code" and use a wrapper around the activity to ensure the state management and simplify it for the engineer. A slight difference but interesting paradigm.

I would say, I believe that, while rarely done - one could define WWF workflows completely through code and that there is a way to serialize workflow as an artifact that could be version controlled, etc. But, how they display that visually and how WWF compiles into the intermediate representation and uses that at runtime does sound different than temporal. I suppose though, having the intermediate representation does perhaps allow for running tests against the workflow logic itself - whereas you shift the tests to the code itself.. so, different implementation but similar idea.

Again, I see how temporal simplifies that from the engineer's perspective, so kudos to you guys. I can see how what you are saying would work and be a helpful approach for a lot of use cases.

[1] https://www.cs.ucdavis.edu/~devanbu/teaching/160/docs/petrin...