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3.2. EXTRACT USER ELEMENTS
I found it useful, in designing for the power plant, to subdivide the user objects and functions I had used in the UI war room into four categories: Information, Objects, Goals, and Actions [borrowed very loosely from the GOMS model (Kieras, 1988) and from object-oriented design]. Examples of the different types of user elements are shown in Table 10.2.
Design Perspective | Example User Element |
---|---|
Information | Tank level Pressure is dangerously high |
Objects | Tank Pneumatic valve |
Goals | Control tank level |
Actions | Start agitator |
To extract the different user elements from the task analysis, I perform a variation of the noun-verb parse used in object-oriented design (Pressman, 1991, pp. 404-408). Given an English description, the nouns in the sentence fall into either the Information or Objects category, and the verbs fall into the Goals or Actions category. Then, it is a relatively intuitive process of dividing concrete objects from information and user goals from actions. (In keeping with the prism analogy, I happen to use different colored highlighters to classify each of these element types, by color, as I read through the text). The process is illustrated in Figure 10.7.
Figure 10.7 Extracting user elements.
I have found not only that these particular categories can be used in a mutually exclusive way, but that they also tend to be exhaustive (covering all of the important pieces of information from the task analysis). I find, also, that this categorization forces me to think about user elements that have not been explicitly defined in the task analysis (e.g., an Action is mentioned in the task analysis, but there is no mention of the Information needed for the user to confirm that it had the desired effect).
As the designer, you may find that Information, Objects, Goals, and Actions are not appropriate for the work you are doing. Though I have found these categorical distinctions to be helpful in my own work, the results may be different in another design context. I encourage you to try out your own user element classification and perspectives from which to design. The same principles of design should still apply, regardless of the categorization used.
Once having divided task analysis data into the four categories, I then take each category individually and approach design from the perspective of that category.
3.3. DEFINE INTERRELATIONS
First I want to define the relationship of each user element in a perspective to related elements in all of the other perspectives (including its own). For instance, if I decide to deal with Information first, then I will draw up a table (the Table of Relations) containing all of the Information elements for one task. For each Information element, I will list any Information, Object, Goal, or Action elements to which it is related. Then I will repeat this process from each of the three remaining perspectives.
I sometimes use brackets after an element in the Table of Relations to further define the nature of the relationship or the options available. For example, I added the options open | closed | partially open, in brackets, after the status of valve Information element in Table 10.3.
Related Elements | |||||
User Element under | |||||
Consideration | Information | Objects | Goals | Actions | |
Pressure is dangerously high (information) | Current pressure | Pressure release valve | Return pressure to normal level | Decrease pressure | |
How long has it been dangerously high? | Tank | Maintain pressure at normal level | Open pressure release valve | ||
At what level did it become dangerous? | |||||
Tank level | | Tank | Control tank level | Increase Decrease | |
Pneumatic valve (object) | Status of valve (open | closed | | ||||
partially open) | | | Open Close | ||
Tank | Tank level | Tank 1, Tank 2, Liquid 1, Liquid 2 | Control tank level | ||
Control tank level (goal) | Tank level | Tank | Maintain tank level at current setpoint | Set a new setpoint at <new volume> | |
Change tank level | Increase (tank level) | ||||
Decrease (tank level) | |||||
Start agitator (action) | Is agitator already started? | Agitator | Keep solute dissolved | | |
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