State and transition

Draws the conditions you can be in as boxes and the moves between them as labeled arrows, so what is open now is visible.

You and your brother have had the same argument four times this year. Afterwards you replay the sentences and decide you should have said something different. The sentences were never the problem. What you cannot see is that the two of you keep moving through a small set of standing conditions, and that only a few doors connect them.

State and transition draws those conditions as boxes and those doors as arrows. A state is a way things currently are, stable enough to name and to notice you are inside. A transition is what moves you out of one, and the arrow carries the trigger written on the line. The drawing answers one question. From where you are standing now, what can happen next, and what would have to occur for it. Anything that is not an arrow out of your current box is not on the table today, however much you would like it to be.

It has four renderers. A state machine is the plain version: named boxes, labeled arrows, one marker for where you are. A statechart nests states inside a larger state, so a trigger that applies to a whole group is drawn once on the boundary instead of repeated on every member. A transition matrix drops the picture and counts: where you were down the side, where you went across the top, a number in every cell. A legal-move map keeps only your current box and fans out the moves open from it, which is what you want when the question is about this week.