GOMS Summary

GOMS is an acronym that stands for GOALS, OPERATORS, METHODS, and SELECTION RULES. A GOMS model is composed of METHODS that are used to achieve specific GOALS. The METHODS are then composed of OPERATORS at the lowest level. The OPERATORS are specific steps that a user performs and are assigned a specific execution time. If a GOAL can be achieved by more than one METHOD, then SELECTION RULES are used to determine the proper METHOD.

• GOALS are a specific state that a users wants to have occur. Selecting a file using a graphical user interface is an example.
• OPERATORS are the low level acts (perceptual, cognitive, and motor) that bring about changes. OPERATOR execution times are often determined from average execution times taken from a number of users (KLM times). Average execution times are appropriate if better estimates are lacking. However, to improve the reliability of GOMS models, studies should be completed to determine the most accurate OPERATOR times.
• METHODS are the sequence of OPERATORS used to achieve a GOAL. GOMS models assume an expert user.
• SELECTION RULES are IF THEN type operations that are used to select between multiple METHODS to achieve a single GOAL.

There are basically four different GOMS techniques that we will discuss in these pages. The four models are the Keystroke-Level Model (KLM), CMN-GOMS, NGOMSL, and CPM-GOMS. These four models vary in complexity and are used to model different activities.

These pages contain a brief overview of the GOMS approach, as well as the entire set of lecture notes used during the class teaching exercises. An example of a GOMS task analysis on a watch that was accomplished as an in-class exercise is also included. A short QuickTime video is available describing the QGOMS software that was used in class, and a review of the final discussion is provided by means of RealAudio clips and a written narrative. A set of ten review questions are provided and are used as preparation for the final exam. Finally, a set of references that were used in preparing the class exercises and the web pages is provided.