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Step 2. Specify the normative (correct) paths for this use case (represented as a goal hierarchy), thus
indicating the alternative sequences of steps that the user could take to successfully achieve the specified
goal. Note that there could be more than one correct path for completing a given task.
Step 3. Identify the state of the product and the associated “world” at each node in the goal hierarchy.
In the case of a software product, the state of the product would be the current appearance of the interface
and any associated internal states (such as the queue of recently completed actions that would be used
should an undo function be applied). The state of the “world” applies if the product or the user actually
changes something in the world as part of an action, such as changing the temperature of a glass man-
ufacturing system when using the interface to a process control system.
Step 4. Generate predictions. For each correct action (node in hierarchy):
.
Predict all the relevant success stories.
.
Predict all the relevant failure stories.
.
Record the reasons and assumptions made in generating these stories.
.
Identify potential fixes to avoid or assist in recovery from failure stories. (Keep in mind that these
fixes could be local patches or bandaids or they could involve proposing a major change in the
design concept.)
Note that, in developing a specific set of predictions, it may be more efficient to consider the use cases
for the full range of users in parallel while stepping through the normative goal hierarchy. For instance,
predictions might be generated for both a first-time user and a frequent user of the product while looking
at each node in the goal hierarchy.
To make this discussion clearer, a sample cognitive walkthrough is provided next. For this illustration,
we will consider the design of a specific online library search system.
Example of Step 1. Select a use case for evaluation. In completing this sample walkthrough, assume as
the use case that we are dealing with a college student in the United States who is a first-time user who has
used other online library search systems before (but is not an expert at library searches), and who also
regularly searches for material on the Web. Abstractly, this means that the user:
.
Is reasonably literate in the English language
.
Is familiar with the use of a keyword entry box and the use of hot links on web pages
.
Knows that menus are often shown along the top of the page as short phrases and that a given
menu item can be selected by clicking on it
.
Knows that library searches are often structured in terms of author, title, and subject searches
.
Is not familiar with the layout and navigation of this specific library system
Assume the user is looking for wedding songs to be performed at her own wedding, that she is con-
ducting the search at home on her own computer over a high-speed connection, and that help from a
librarian is available only by phone. Assume further that she wants CDs to listen to (she only has a
CD player), rather than sheet music, tapes, etc.
Example of Step 2. Specify the normative (correct) paths for this use case. Such a normative model is gen-
erally best represented as a goal
subgoal hierarchy (Preece, 1994). The high-level goal or task is represented
as the top node in the hierarchy, and each level below a node represents the subgoals that will achieve the
goal represented by that higher level node. Relationships among subgoals can be indicated by OR (com-
pletion of either subgoal alone is sufficient to achieve the higher level goal), AND (both subgoals must
be completed to achieve the higher level goal, but in any order) or sequence (both subgoals must be
completed to achieve the higher level goal, and they must be completed in a specified order) operators.
In this example, the initial screen that this student will access is shown in Figure 24.1 and Figure 24.2.
For this user the top section of the normative model or goal hierarchy is shown in Figure 24.3. Note that:
/
.
The highest node is the student's goal or task in this use case (finding wedding songs on CDs)
.
The nodes below this highest node represent four different ways the student could successfully
begin (and are therefore marked with OR)
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