1. Models and Theories

2. 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?
Piftall: Closure of the out loop before all subtasks have been completed may result in the original article being left in the photo copier

3. Goal: PHOTOCOPY-PAPER
Goal: LOCATE-ARTICLE
Goal: PHOTOCOPY-PAGE repeat until no more pages
[Select Goal: 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
REMOVE-COPY (outer goal satisfied!)
Goal: RETRIEVE-JOURNAL
OPEN-COVER
REMOVE-JOURNAL

4. 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.

5. Closure to Outer Goal, must force user to collect copy last
Goal: PHOTOCOPY-PAPER
Goal: LOCATE-ARTICLE
Goal: PHOTOCOPY-PAGE repeat until no more pages
[Select Goal: 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
Goal: COLLECT-COPY
REMOVE-COPY (outer goal satisfied!)
Closure to Outer Goal, must force user to collect copy last

6. 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.
Warning sound.
Copy cards can be withheld until cover is lifted.
Some of these are used by ABMs to ensure that bank cards are not left in the machine.

7. 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.

8. 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 “ and /
Consecutive delimiter space and “

9. 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

10. 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
We assume the copy will take some time to complete.
The logout task has been cognitively processed during the R. We do not count this M.

11. 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.

12. 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

13. 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

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

15. 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.

16. Alternate B – Represents mouse click 0.1 sec.
BB – Double mouse click 0.2 sec.
Consider editing the string.
dcl “are” do scl <locate cursor> 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 seconds.
Note: Basic times vary depending on skill of user.
Eg. M can range from 0.6 to 1.35.

17. 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.

18. 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.

19. Goal Orientated Help 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.