Drawing a Structure Diagram

To draw a structure diagram, you record the problem's decomposition level by level, from the whole job down: the whole job in the top box, its main subsections underneath, then each subsection split into its own smaller tasks until every box is a single small task.

1. Start with the whole problem. The top box names the complete job, not the first step. For a program that plans transport for a school trip, the top box would read Plan buses for a school trip.
2. Add the main subsections. Give each big job its own box and join it with a line to the top box. Between them they must do everything the top box promises: Count people going, Find seats per bus and Work out buses needed.
3. Break each subsection down in the same way. Treat a subsection as a small problem and add its tasks on the next level, each joined to that subsection alone. Count people going becomes Ask each class for its number and Add the class numbers; Work out buses needed becomes Divide people by seats per bus and Round up to a whole bus.
4. Stop at a single small task. If a box already describes one small task that needs no further splitting, it needs nothing below it, so different branches can end at different depths.

Work in passes rather than filling in every level at once: draw the top two levels, check the subsections cover the whole problem with nothing missing or spare, then push down one branch at a time. Keep each box joined only to the box directly above it, so tasks stay grouped under the subsection they belong to instead of being strung out as a line of steps.