GOMS Model

GOMS (Goals, Operators, Methods, and Selection rules) is predictive model of human information processing used for task analysis in human computer interaction design. The model was proposed by Stuart Card, Thomas P. Moran and Allen Newell in 1983. The model is used to analyze user’s physical , cognitive and perceptual interactions with computer while achieving a task or a goal in best possible way.

Goals are what users intend to do. Operators are actions they perform to achieve their goals. Methods are operator sequences that accomplish a goal. Multiple methods can exist to accomplish same goal. Selection rules describe when a user will select a method over the other.

In Key Stroke Level (KLM) GOMS model the physical, cognitive and perceptual actions during a task is decomposed in form of fundamental keystroke sequence. The model specifies time required for each fundamental keystroke. Thus we can predict the total time of completing a task. Multiple methods can be compared based on the total time to complete a task in order to determine which is the most efficient method for accomplishing the task is.

Following example of basic GOMS model is taken from John & Kieras (1996b) . It models the task of moving text in a word processor, in the context of editing a manuscript. Note the use of sub goals and selection rules, which do not exist in KLM.

 

GOAL: EDIT-MANUSCRIPT
.     GOAL: EDIT-UNIT-TASK ... repeat until no more unit tasks
.     .     GOAL: ACQUIRE UNIT-TASK
.     .	    .	  GOAL: GET-NEXT-PAGE ... if at end of manuscript page
.     .	    .	  GOAL: GET-FROM-MANUSCRIPT
.     .	    GOAL: EXECUTE-UNIT-TASK ... if a unit task was found
.     .	    .	  GOAL: MODIFY-TEXT
.     .	    .	  .   [select: GOAL: MOVE-TEXT* ...if text is to be moved
.     .	    .	  .       GOAL: DELETE-PHRASE ...if a phrase is to be deleted
.     .	    .	  .       GOAL: INSERT-WORD] ... if a word is to be inserted
.     .	    .	  .     VERIFY-EDIT

*Expansion of MOVE-TEXT goal
GOAL: MOVE-TEXT
.     GOAL: CUT-TEXT
.     .     GOAL: HIGHLIGHT-TEXT
.     .		.	[select**: GOAL: HIGHLIGHT-WORD
.     .		.		   .   MOVE-CURSOR-TO-WORD
.     .		.		   .   DOUBLE-CLICK-MOUSE-BUTTON
.     .		.		   .   VERIFY-HIGHLIGHT
.     .		.	   	   GOAL: HIGHLIGHT-ARBITRARY-TEXT
.     .		.		   .	 MOVE-CURSOR-TO-BEGINNING	1.10
.     .		.		   .	 CLICK-MOUSE-BUTTON		0.20
.     .		.		   .	 MOVE-CURSOR-TO-END		1.10
.     .		.		   .	 SHIFT-CLICK-MOUSE-BUTTON	0.48
.     .		.		   .	 VERIFY-HIGHLIGHT]		1.35
.     .		GOAL: ISSUE-CUT-COMMAND			
.     .		.     MOVE-CURSOR-TO-EDIT-MENU				1.10
.     .		.     PRESS-MOUSE-BUTTON				0.10
.     .		.     MOVE-CURSOR-TO-CUT-ITEM				1.10
.     .		.     VERIFY-HIGHLIGHT					1.35
.     .		.     RELEASE-MOUSE-BUTTON				0.10
.     GOAL: PASTE-TEXT
.     .	    GOAL: POSITION-CURSOR-AT-INSERTION-POINT
.     .		MOVE-CURSOR-TO-INSERTION-POIONT				1.10
.     .		CLICK-MOUSE-BUTTON					0.20
.     .		VERIFY-POSITION						1.35
.     .		GOAL: ISSUE-PASTE-COMMAND
.     .		.     MOVE-CURSOR-TO-EDIT-MENU				1.10
.     .		.     PRESS-MOUSE-BUTTON				0.10
.     .		.     MOVE-MOUSE-TO-PASTE-ITEM				1.10
.     .		.     VERIFY-HIGHLIGHT					1.35
.     .		.     RELEASE-MOUSE-BUTTON				0.10
					TOTAL TIME PREDICTED (SEC)     14.38

Based on the above GOMS analysis, it should take 14.38 seconds to move text.