<aside> 🚩 A Usage Scenario (US) is a description of the steps needed to achieve a goal with a specific intervention, used to facilitate study of interactions between human users and the intervention.
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A well-designed intervention must interact well with its users. To study those interactions, they must be documented first. A Usage Scenario is a tool meant to let designers document the steps needed to use an intervention.
A US must cover the three main parts of any use of an intervention: setup (or initialization), actual use, and put-away (or finalization).
In this course, a US is a simple nested, numbered list. The first level always has exactly 3 elements, for setup, use, and put-away. The nested levels simply capture, in order, the steps for the main parts of the US. Branches can be simulated with steps that instruct the reader to "go to" another step.
Each step can be referenced by simply naming the nested numeric sequence of that step. For instance, the third step in the Setup part of a US would be step 1.3.
Obviously, you cannot fully describe the US of an intervention you have yet to design, so you will revisit the US often, to refine and expand it as your design proceeds.
Consider this example:
<aside> <img src="https://s3-us-west-2.amazonaws.com/secure.notion-static.com/165bf257-370c-49c5-ab0b-3761906873c3/Goals.png" alt="https://s3-us-west-2.amazonaws.com/secure.notion-static.com/165bf257-370c-49c5-ab0b-3761906873c3/Goals.png" width="40px" /> Design a writing instrument (WI) for use on paper. The WI must be portable and must leave permanent marks on paper. (This eliminates pencils, quills, and desk pens as possible classes of designs.)
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Consider the example of designing a writing instrument (WI). Let us assume the WI must be portable and must leave permanent marks on paper. (This eliminates pencils, quills, and desk pens as possible classes of designs.)
At the very beginning of such a project, one possible US might be as shown below.
<aside> 💡 US for WI, Version 1
Pay particular attention to the phrasing of the steps.
Notice how no mention is made of the structure of the writing instrument.
It is essential to keep the steps of a US free of mention of any part, assembly, or material of the intervention that cannot be based on evidenced design decisions previously made by the designers.
USs involve only interactions between users and the intervention. If the intervention is not involved directly in a step, then that step can be removed from the US.
For instance, in the case of a US for a writing instrument, we do not involve steps that have to do with setting out the paper on which the user will write, or turning the page when the user has filled one side with writing.
At some future point in the project, you will have determined some aspects of the WI's design. Two possibilities in this regard are (a) that the WI will use a replaceable cartridge, and (b) that the writing tip will retract with a conventional mechanism built into the top of the WI. You will have to enhance the US to capture the implications of these design decisions. One possibility is shown below.
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US for WI, Version 2
Note the differences between the original and revised USs.
For instance, the original US's step 1.2, Activate the WI, has been change (step 1.3 of the revised US) to specify how the WI is activated.
Notice also the mention of hand grips. The choice of grip is a consequence of the design decision about the type of retraction mechanism.
In Version 2 of the US, all references to specific features of the WI are justifiable with respect to previously made design decisions.
Finally, note that each step in the US can be analyzed as a Human-Machine Interaction Loop. The importance of this will become evident in the Critique stage of the Study, Propose, Critique Loop.
Initially, because you don't have any design concepts yet, you should develop a single US collaboratively with your team. However, when each team member eventually has their own concept to develop, you will need to develop variations of the US - one for each concept.
