State Machines and Business Users | Greg Young


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I was at a workshop over the weekend talking about the use of Finite State Machines as coordination mechanisms for systems. These things might be called sagas, activities, workflows, process managers (my preferred term lately from PEI), orchestrations, choreographers, and I am sure I am leaving out a few.

One of the guys in the talk (quite knowledgable) brought up that they used to use petri nets for this as well as pure finite state machines and there had been a push to more procedural mechanisms as business users don’t think in terms of finite state machines. I noted that while we have been moving to more procedural methods, as most of these procedural methods are in their hearts asynchronous our procedural techniques tend to be domain specific languages that internally generate state machines anyways, often based in the join calculus (think futures or the async keyword in C# when joining).

However later in the day I had a realization connecting two things. We like to describe business situations in gherkin style (not strict) specifications.

Given: Some initial starting point
When: Something happens
Then: Something occurred

We as an industry have been very successful getting specifications written in this style. We regularly do analysis and write acceptance criteria using this style. Business users seem to have been fairly capable of understanding it.

This style is basically describing a state machine.

Given: some initial state
When: a stimulus
Then: Something occurred (message/transition depending on style of testing)

How can we be so successful with this style of specification and in the next breath say that business users can’t understand state machines? The trick is they don’t understand the actual machine but they understand (and can specify very well) the exterior behaviours of such a machine.

Try getting a business user to create for you the state machine to control a simple DVD player for you. Likely they will scratch their heads and politely become very busy so they won’t be able to attend the next meeting. Try getting them to specify

Given a video is playing
When fast forward is pressed
Then the play goes at double speed

Maybe the problem here that caused our move towards procedural style controllers was the goal all the middleware seems to push of having business users writing the activities as opposed to reading about/specifying/understanding them. I have yet to see in all the organizations I have been to a single one where the dream of having business users creating these types of long running procedures actually panned out. to be fair: I have seen it work but the business user had formerly been a developer and BA