Models and Theories

GOMS Example Photocopying an article Create a GOMS description of the task of photocopying an article from a journal. Assume –copy 1 page at a time –cover must be over the imaging surface of the copier before a copy can be made. What can the pit fall of this design be?

Goal: PHOTOCOPY-PAPER Goal: LOCATE-ARTICLE Goal: PHOTOCOPY-PAGE repeat until no more pages [SelectGoal: SELECT-PAGE --> CHOOSE-PAGE-TO-COPY] Goal: ORIENT-PAGE OPEN -COVER POSITION-PAGE CLOSE-COVER PRESS-BUTTON Goal: VERIFY-COPY LOCATE-OUT-TRAY EXAMINE-COPY Goal: COLLECT-COPY LOCATE-OUT-TRAY REMOVE-COPY (outer goal satisfied!) Goal: RETRIEVE-JOURNAL OPEN-COVER REMOVE-JOURNAL CLOSE-COVER

GOMS and Selection Rules Selection rules exist if a spoiled copy was printed. Consider the following: Rule 1: SELECT-PAGE if last page was copied successfully or start of article. Note: The goal SELECT-PAGE is only valid if we are at the start of the article or the last copy was successful. If the last copy was spoiled the we must recopy the current page, so only a re-orientation would be required.

Goal: PHOTOCOPY-PAPER Goal: LOCATE-ARTICLE Goal: PHOTOCOPY-PAGE repeat until no more pages [SelectGoal: SELECT-PAGE --> CHOOSE-PAGE-TO-COPY] Goal: ORIENT-PAGE OPEN -COVER POSITION-PAGE CLOSE-COVER PRESS-BUTTON Goal: VERIFY-COPY LOCATE-OUT-TRAY EXAMINE-COPY Goal: RETRIEVE-JOURNAL OPEN-COVER REMOVE-JOURNAL CLOSE-COVER Goal: COLLECT-COPY LOCATE-OUT-TRAY REMOVE-COPY (outer goal satisfied!) Closure to Outer Goal, must force user to collect copy last

GOMS We need to force the outer goal. –Possible Solution Do not eject the page unless the cover is up. Warning light if something is left in the copier. Copy cards can be withheld until cover is lifted.

Table 4.1 Raskin Placing the M’s Rule 0 - Insert Ms in front of all Ks. In front of Ps but not arguments of those commands. – E.g. Menu sub selection Rule 1 - Delete anticipated Ms –If we point and click then the click takes no mental preparation. It is an automated response. Rule 2 - Delete Ms in cognitive units –Cognitive units are “chunks” of actions which are performed as a unit. Like typing a short sentence. 1 M needed for whole string.

Table 4.1 Raskin Placing the M’s Cont... Rule 3 - Deletion of Ms before consecutive terminators. –E.g. copy “3p94 marks.xls” /backup Consecutive delimiter space and “ Consecutive delimiter “ and /

Table 4.1 Raskin Placing the M’s Cont... Rule 4 - Deletion of Ms that are terminators. –E.g. –Terminators are habitual and thus become part of the string. –No thought required to execute rm *.*  Carriage return is delimiter

Table 4.1 Raskin Placing the M’s Cont... Rule 5 - Deletion of Overlapped Ms. –Delays R caused by the system which overlap a M does not count. –User is waiting for the system. The fact that they are thinking about the next task is masked by the system delay. –E.g. cp *.*..  logout  –MkkkMkkkMkk R Mkkkkkk –The green M is removed since the user is waiting for the system to respond R –The logout task has been cognitively processed during the R. We do not count this M.

GOMS example We wish to solve an age old debate. Is using just keyboard commands to edit a string faster or slower then using a mouse and a keyboard to edit the same string. We assume expert knowledge –Users are trained and proficient.

GOMS example cont... Given the following string –Hi! how are you. Edit this string to read: –Hi! how do you do. Assume the cursor is at the beginning of the string. What is the relative time measure if we were to edit this string in NotePad using. –Keyboard –Keyboard Mouse

GOMS example Cont... Keyboard –We have knowledge of short cuts such as: CTRL + arrow skips to beginning of next word CTRL + Shift + right arrow highlights word. ^  ^  ^  do  ^    do KK KK KK KKK KK K KKK MKMK MKMK MKMK MKMKMK MKMK MK MKMKMK Delete Ms in cognitive unit. MKK KK MKK MKKK MKK MK MKKK –6 Ms = 6*1.35 = 8.1 –15 Ks = 15 *0.2 = 3 –Total 11.1 seconds

GOMS example Cont... Keyboard Mouse –dcl = double click of mouse –scl = single click of mouse dcl “are” do  scl  do MHPMKMK MHKMKMK HMPMK MHKMKMK Delete anticipated Ms MHPKK MHKMKMK HMPK MHKMKMK Delete Ms within cognitive units MHPKK MHKKK HMPK MHKKK

GOMS example Cont... –4 Ms = 4 * 1.35 = 5.4 –2 Ps = 2 * 1.1 = 2.2 –4 Hs = 4 * 0.4 = 1.6 –9 Ks = 9 * 0.2 = 1.8 –Total 11 seconds. Note there is almost no difference between the two methods. Argument solve.

Alternate B – Represents mouse click 0.1 sec. BB – Double mouse click 0.2 sec. Consider editing the string. dcl “are” do  scl  do MHPMBMB MHKMKMK HMPMB MHKMKMK –4 Ms = 4 * 1.35 = 5.4 –3 Bs = 3 * 0.1 = 0.3 –2 Ps = 2 * 1.1 = 2.2 –4 Hs = 4 * 0.4 = 1.6 –6 Ks = 6 * 0.2 = 1.2 –Total 10.7 seconds. Note: Basic times vary depending on skill of user. –Eg. M can range from 0.6 to 1.35.

NYNEX The US telephone company NYNEX was intending to install a new computer system to support their operators. Before installation a detailed GOMS analysis was performed taking into account the cognitive and physical processes involved in dealing with a call. Because an operator performs several activities in parallel a PERT-style GOMS description was constructed. The PERT analysis was used to determine the critical path, and hence the time to complete a typical task. It was discovered that rather than speeding up operations, the new system would take longer to process each call. The new system was abandoned before installation, leading to the savings of many millions of dollars.

How to Evaluate using KLM Gives a relative time when all other things can be considered equal. Must ensure there is no variance in: –Knowledge w.r.t. system, all users have functional knowledge of system. –Users, all are trained equally well on both systems. –Same tasks are performed on each system. Other factors for the KPH & M’s do exist. These are relative to system.

Outer Goal - Connect to the Internet Sub-Goals - listed as steps 1to7 GOMS can be used to analyze how a user solves problems and then create a help system which takes advantage of this model. The model will mirror the thought process of solving the problem. Goal Orientated Help System