Worked example · Design Technology · Year 8
DCF: Data and computational thinking → Problem-solving and modelling
A secure Year 8 response to all four parts, including the finished flowchart. Show the flowchart after pupils have drawn their own — it is the answer, and they will copy it. The two things to look for when marking are the labelled Yes/No arrows and at least one arrow that goes back up the page.
| Inputs | Processes | Outputs |
|---|---|---|
| 225 g self-raising flour 110 g cubed cold butter 85 g caster sugar 50 g currants ½ tsp mixed spice 1 beaten egg Up to 2 tbsp milk — a conditional input, only used if the dough will not hold together Heat, at a medium setting Extra butter and sugar for greasing and dusting |
Rub butter into flour Stir in sugar, currants and spice Add egg and mix to a firm dough Add milk a spoonful at a time and re-mix Roll out to 5 mm Cut 6 cm rounds Re-roll the offcuts and cut again Grease and heat the bakestone Cook the first side for 2 minutes Look underneath and judge the colour Turn over and cook the second side Move to the rack and dust with sugar |
12 to 14 cooked Welsh cakes, dusted with caster sugar, on a cooling rack Also an output, even though you do not eat it: the information "the underside is golden brown", which is what the decision in the flowchart uses |
The equipment is neither. It is a resource — a tool the process needs but does not consume or produce. The bowl is still a bowl at the end; the 225 g of flour is gone. An algorithm still has to list it, for two reasons. First, the steps are impossible without it: "cut out rounds" means nothing without a cutter. Second, the equipment fixes the numbers — it is the 6 cm cutter and the 5 mm thickness that make the yield 12 to 14 rather than some other number, and it is a bakestone rather than an oven, which is why the cakes are cooked in batches on two sides.
Evidences criterion 1: the three columns are sorted correctly, milk is identified as a conditional input, and the answer about equipment explains why it matters instead of just naming it.
Criterion 2: one instruction per line, every amount and time lifted from the recipe, and the three repeats are written with the condition that ends them. Step 9 also carries a limit of 2 tablespoons, which is what stops the loop running forever.
Reading the loops. There are three arrows that go back up the page. The milk loop re-tests the dough after each spoonful and gives up at two spoonfuls. The dough loop sends you back to roll the offcuts and cut again until there is nothing left. The batch loop sends you back to the bakestone until every round has been cooked. The colour check is the fourth decision point and it loops in place, adding 30 seconds at a time.
Criteria 3 and 4: terminators are rounded, the ingredients and the finished cakes are parallelograms, everything you do is a rectangle and every question is a diamond with both exits labelled. Three separate loops go back to an earlier step, and each one has a condition that ends it.
Why the milk cannot be one process box. Because it is not one action, it is an action plus a test, repeated. "Add milk until the dough comes together" needs you to add a spoonful, mix, look, and then either stop or go round again — and a process box runs once and has no way of asking a question. So it has to be a process box with a decision after it and an arrow going back. It also needs a limit: the recipe says two tablespoons is as far as you go, because too much milk makes the dough sticky and the cakes tough. Without that limit the loop could keep adding milk forever, which in computing is an infinite loop and in cooking is a bowl of batter.
Why the colour check has to come after the cooking, not before. If the diamond came first, the very first test would happen the moment the raw dough hit the bakestone, so the answer would always be No, and the loop would then cook in 30-second chunks from cold and never do the 2 minutes the recipe asks for. Put the cooking first and the test second, and the 2 minutes always happens exactly once and the 30-second top-ups only happen if they are needed. In programming that is the difference between a loop that checks before it acts and one that acts before it checks — and here, only one of them makes an edible cake.
Criterion 5: it explains why a conditional repeat cannot collapse into a single process box, spots the infinite-loop risk and the recipe's own limit, and gets the order of the cook-then-check loop right for the right reason.