Building flows

Branches and decisions

A flow branches on the state of an object. Whoever sets the state, an agent, a person or a rule, decides which processes run next. This page builds a ticket triage that takes one of two paths and rejoins.

An agent picks the branch

1. Give the object its states

   Right-click Ticket and Add state twice: bug and feature.

2. Have an agent review it

   Add an agent Classify that takes Ticket, and link it back to Ticket itself (not a state). Select that link and press Decide a state to tick both states. Because Classify takes Ticket too, it is a review: Ticket keeps the content the person entered and only gains a state.

3. Start each branch from a state

   Drag from the bug pill's handle onto Attempt fix, and from feature onto Write spec. These are event links: each process runs when Ticket enters its state.

Rejoining the branches

Summarize takes both Spec and Fix, but only one of them is ever generated. Left alone it would wait forever and the run would end without a summary. Two ways to rejoin:

A quorum

Set Needs in Summarize's settings to 1. It runs once one of what it takes exists. This is the simplest rejoin when the branches are triggered by events.

Conditions

Alternatively, make the branches conditions, so the branch not taken is skipped and its output is settled as absent. Summarize then runs with whichever exists, no quorum needed.

A condition is checked as soon as its process is ready, so it must be on an object that only exists once the decision is made. Ticket won't do: it exists, in no state, from the moment the person enters it. Have Classify generate a separate Triage object in the state it decides, link both branches from Triage's states, select each link and choose only if in it. Both branches also take Ticket plainly, for its content.

Branching on a value with rules

Scripts and Sentry steps can't decide a state, and sometimes the branch is just arithmetic. Give the states rules instead. A Health object with states down (status != 200), slow (ms > 2000) and fine (ms <= 2000) comes out in the first state whose rule holds, and the processes linked from those states run. It also turns an agent's numeric judgement into a branch, such as confidence >= 0.8.

Fanning in: several opinions

A quorum also gathers votes. Ask three agents, each with a different Model, whether a migration is safe; each yields its own verdict with states safe and unsafe. The process that runs the migration takes the Migration plus each verdict through a condition on safe, with Needs set to 3.