Problem boundaries, context and assumptions

Choose what you are studying

A system is a set of interacting parts considered together for a purpose. A boundary marks which parts we include in a particular model. For the organiser, we could include the tray, its labels and its tool positions. The shelf and people remain outside that boundary, but they still interact with the tray.

An interface is a place where parts or systems meet and exchange something. The tray meets the shelf through contact and fit. People interact through reaching, reading, grasping and returning. A boundary diagram helps us notice these relationships before detailed drawings distract us.

The boundary is chosen to answer a question. If we are studying time spent locating tools, labels and working habits matter. If we are studying how the organiser is carried, its contents and lifting points matter. A useful model can change with the question.

Outside the boundary can still affect success

Imagine the team may change the tray but may not replace the shelf. The shelf's clear space becomes a condition the tray must fit. ‘Outside our design control’ does not mean ‘irrelevant’. A team can investigate, document and negotiate an external condition even when it cannot change it directly.

Write down the intended setting: which shelf, which tools, whether the tray stays in place, and who moves it. Include occasional tasks such as cleaning. A solution designed only around the busiest five minutes may fail during the quieter work that keeps the workshop running.

Make an uncertain belief easy to revisit

An assumption is something accepted provisionally so work can proceed. ‘The tool set will stay the same this term’ is an assumption if nobody has confirmed it. ‘There are twelve tools in the photographed set’ is a recorded observation about that set. ‘The organiser must fit the existing shelf’ is a project condition if agreed with the coordinator.

Attach a question to each consequential assumption: who can check it, what evidence would help, and which choice would change if it were false? In our example, a fixed set favours closely fitted positions; a changing set may favour adjustable dividers. We can explore both while waiting for confirmation.

Follow one assumption into a design change

The first sketch assumes the organiser never leaves the shelf. A volunteer then describes carrying it to another room. That new use creates questions about carrying, retention of contents and the route between rooms.

The team has two clear choices: include carrying in the design brief, or agree that tools are moved another way. Leaving the assumption unspoken would let different people believe different tasks were covered.

Record the decision and its reason. If carrying becomes part of the task, revisit the boundary and the relevant requirements. We have changed the problem deliberately instead of quietly extending the claims made for the first sketch.

Try the reasoning

1. Does an item outside your system boundary have no effect on the design?

   Show the answer and reasoning

   It can have a large effect. The shelf is outside the tray model but determines fit; people outside it determine whether reaching and returning work.

2. How would you check ‘the tray will never be moved’?

   Show the answer and reasoning

   Walk through use, cleaning and storage with the people responsible. Record whether moving is excluded or included, rather than treating the designer's expectation as a fact.

3. Why might two valid diagrams show different boundaries?

   Show the answer and reasoning

   They may answer different questions. A location model and a carrying model need different details, provided their scope and interfaces are explicit.

What to carry forward

Draw the boundary, follow its interfaces, and record the assumptions that could change your choice.