Methodology I: Task Analysis - Foundations for Designing User-Centered Systems - page 314

Table 11.3 The components of GOMS
Goals are the desired states of affairs. They are brought about by the application of methods and
operators
Operators are elementary perceptual, motor, or cognitive actions. Intended either to change the
world (a normal key-press) or to change our knowledge about the world (e.g., reading). In
practice, operators are really those subgoals whose methods of solution we have decided not
to analyze any further. The choice of appropriate operators is critical to a GOMS analysis.
Some critics note that there are no clear guidelines for doing so, although it is often a fairly
straightforward decision
Methods describe procedures for achieving goals. They contain a sequence of subgoals and/or
operators, with conditions potentially attached to each part of the method. These conditions
relate to the current task environment (e.g., repeat until no tasks left)
Selection rules augment the basic control structure of the model. Where multiple methods are
available the selection rules indicate how to choose between the methods. These include, for
example, when scrolling a document: if you want to scroll a long distance, use the search
function; if you want to scroll a short distance, use the scroll bar; and if you want to scroll a
very short distance, use the arrow keys
Table 11.4 Example GOMS model for text editing (reprinted from St. Amant
et al. 2005 ). This model is written using NGOMSL notation
LTM [long term memory] item: Cut Command [a unit task]
Name is Cut.
Containing Menu is Edit.
Menu Item Label is Cut.
Accelerator Key is “Control-X”.
[[There would be more types of commands here in a complete model.]]
Method for goal: Edit Document
Step. Store First under <current task name>.
Step. Check for done.
Decide: If <current task name> is None, Then
Delete <current task>;
Delete <current task name>;
Return with goal accomplished.
Step. Get task item whose
Name is <current task name>
and store under <current task>.
Step. Accomplish goal: Perform Unit task.
Step. Store Next of <current task>
under <current task name>;
Goto Check for done.