Think First

A function block is easier to choose when the required behaviour is described before the block name is discussed.

A client wants a hallway to respond helpfully when someone arrives after dark, but has not described the exact logic.

Turn a request into a behaviour model

A behaviour model names an input (what changes), a decision or condition (what matters), and an output (what should happen). A function block is a reusable logic unit that can implement a defined behaviour; it is not the requirement itself.

For the hallway, “arrival is detected” is the input, “the space needs light” is the condition to clarify, and “a welcoming light scene is requested” is the desired output. Whether a particular block fits comes after the team tests that wording.

This model exposes missing decisions early. For example, it asks what should happen when daylight is already sufficient rather than hiding that question inside a block choice.

1. Separate input, condition, and output in the example.
2. Write a second behaviour model for a meeting-room arrival.
3. Name one missing condition that must be agreed before choosing logic.