NGOMSL is an acronym for Natural GOMS Language, which is a structured natural language used to represent the user's methods and selection rules. NGOMSL models thus have an explicit representation of the user's methods, which are assumed to be strictly sequential and hierarchical in form. The execution time for a task is predicted by simulating the execution of the methods required to perform the task. Each NGOMSL statement is assumed to require a small fixed time to execute, and any operators in the statement, such as a keystroke, will then take additional time depending on the operator. The time to learn how to operate the interface can be predicted from the length of the methods, and the amount of transfer of training from the number of methods or method steps previously learned. Thus estimating times for learning and execution both require counting the number of NGOMSL statements involved; details on this process will be provided in this article.
One important feature of NGOMSL models is that the "how to do it" knowledge is described in a form that can actually be executed – the analyst, or an appropriately programmed computer, can go through the GOMS methods, executing the described actions, and actually carry out the task. A GOMS model is also a way to characterize a set of design decisions from the point of view of the user, which can make it useful during, as well as after, design. It is also a description of what the user must learn, and so can act as a basis for training and reference documentation.
NGOMSL is based on the cognitive modeling of human-computer interaction by Kieras and Polson (Kieras & Polson, 1985; Bovair, Kieras, & Polson, 1990). As summarized by John and Kieras (1994), NGOMSL is useful for many desktop computing situations in which the user's procedures are usefully approximated as being hierarchical and sequential.
Example of NGOMSL
- Goal: Move a file into a subfolder in Windows XP
- Method for accomplishing goal of moving a file using the drag and drop option:
Step 1: Locate the icon of the source file on the screen
Step 2: Move mouse over the icon of the source file
Step 3: Press and keep holding the left mouse button
Step 4: Locate the icon of the destination folder on the screen
Step 5: Move mouse over the icon of the destination folder
Step 6: Release left mouse button
Step 7: Return with goal accomplished
- Method for accomplishing goal of moving a file using the cut and paste option:
Step 1: Recall that the first command is called "cut"
Step 2: Recall that the command "cut" is in the right click menu
Step 3: Locate the icon of the source file on the screen
Step 4: Accomplish the goal of selecting and executing the "cut" command
Step 5: Recall that the next command is called "paste"
Step 6: Recall that the command "paste" is in the right click menu
Step 7: Locate the icon of the destination folder on the screen
Step 8: Double click with left mouse button
Step 9: Locate empty spot on screen
Step 10: Move mouse to the empty spot
Step 11: Accomplish the goal of selecting and executing the "paste" command
Step 12: Return with goal accomplished
Selection rule set for goal: Move a file into a subfolder in Windows XP
If custom icon arrangement is used Then
accomplish goal: cutting-and-pasting.
If no custom icon arrangement is used Then
accomplish goal: drag-and-drop.
Return with goal accomplished.