Chapter 3 : Normative Chapter 3 : Normative ApproachesApproaches

“The one best way”“The one best way”

Chapter 3 : Normative Chapter 3 : Normative ApproachesApproaches

“The one best way”“The one best way”

홍 승 권 홍 승 권

Three Generations of Work Analysis Methods (Rasmussen 1997)

Normative models : how a system should behave– Tayloristic work methods analysis, traditional ta

sk analysis, GOMS analysisDescriptive models : how a system actually

behaves in practice– Critics from anthropological, activity theory and

naturalistic decision making communities– The assumptions they make about human work

are not realistic and not very useful– There are problems in deriving implications for d

esign from descriptive work analysis techniques

Three Generations of Work Analysis Methods (Rasmussen 1997)

Formative models : Requirements that must be satisfied so that the system could behave in a new, desired way.– To help us specify the design attributes that

computer-based information systems should have to satisfy

Normative Approach : Task Analysis

Definitions– To examine “ the tasks that must be

performed by users when they interact with systems”

– The study of what an operator is required to do in terms of actions and/or cognitive processes to achieve a system goal

One best way– For identifying the ideal ways in which the

job should be performed

Three levels of task analysis techniques

Level 1 : input-output– Identify inputs, outputs, and constraints– Constraints that must be taken into account in

selecting the actionsEx) Rate of gasoline consumption

– Two relevant constraints : the number of kilometers in a mile and the number of liters in a gallon

– Several different set of actions• Using a calculator : Reading → Typing into the

calculator• Using metal arithmetic :

Rate of gasoline consumption in an automobile

Task

INPUTS

OUTPUTS

Miles traveled since last fill-upGallons at this fill-up

Automobile gas consumption rate in Km/L

CONSTRAINTS : 1 Mile = 1.609 km

1 Gallon = 3.785 Liters

Level 1 : input-output

A very high level product description of the task– 행위에 대한 constraint 는 다른 형태일 수 있다 . 연료소비의

예에서는 변수들 사이의 관계였다 . Constraint 는 어떤 순차적 절차일 수도 있다 .

– 이들 constraint 를 고려하지 않고 정확히 작업을 수행하는 것은 불가능하다 . 그러나 작업이 실제 어떻게 수행되는 것과는 독립적이다 .

– Constraint 들은 문제상태공간을 줄이는 기능을 한다 . 그러나 단일 행동절차를 지적하지는 않는다 . 단지 가능한 행위 절차의 선택폭 ( 자유도 ) 을 제한한다 .

Level 2 : Sequential Flow

To identify ordered sequence of actions– Flowchart of the process that workers should

follow to perform the task.Ex) Rate of gasoline consumption

– Read current odometer value– Read odometer value at last fill-up– Calculate the difference to obtain miles traveled

since last fill-upEX) Fig 3.2This level of task analysis is usually

dependent to the device workers currently have available to perform the task– If you had a trip odometer, --- just read

Level 3 : TimelineTo identify ordered sequence of

actions with duration estimates for each action– The most detailed of all

Ex) Rate of gasoline consumption– 0-1 s: Read current odometer value– 1-2 s: Read odometer value at last fill-up– 2-3 s : Calculate the difference ….

Ex) Fig. 3.3Only one right way to perform this task

– All of the discretion has been eliminated.

Goal Goal Goal

Level 1 : Input-output

Level 2 : Flow Sequence

Level 3 : Timeline

Constraints VS Instructions

(Three levels of task analysis)

Implications

Different forms of work analysis make different assumptions about the nature of work

So they lead to different designs, which in turn, lead to different types of guidance to workers.

Constraints VS Instructions

Instruction based task analysis

Constraint based task analysis

분석의 정도 Detailed Not detailed

Discretion to worker Less More

What to do To follow the work flow (procedures)

To decide about how to perform the task

Human error Less More

View on people In an pessimistic light

In an optimistic light

Level of variability in worker action

Little variability Large variability

Learning opportunity( 비상대처 능력 )

Less (less) More (more)

Device dependency Device-dependent Device-independent

ConclusionsSeveral advantages of constraint-based

approach– More discretion– Greater variability in action– Fewer assumptions about the properties of the

device It is more likely that the new design will

result in new functional possibilities,– rather than being constrained by designer’s

current assumptions about functionality Task-artifact cycle : Instruction-based

approach 의 단점두 가지 접근방법의 장점을 활용하자

The view from control theoryTo understand goal-oriented behavior,

using control theory– In a conceptual level

Goal +

-

Error

Worker

Action

Plant

Output

A simple model of goal-directed behavior

Goal (g), Output (o), Error (e), Action (a)

Control strategy by the worker (W), dynamics of the plant (P)

A simple model of goal-directed behavior

관계식 – action(a) = strategy(W) * error(e)– error (e) = goal state(g) – output(o)– a= w(g-o)

만약 (w, g, o) 를 안다면 , action sequence를 예상할 수 있다 . ( 초기상태 t=0, g=o)– 초기상태가 알려지지 않으면 , action 을

예측하지 못함 . – 만약 W 가 불확실하면 , action 을 예측하지 못함 .

(STS 에서 여러 가지 전략 가능 )

A complex model of goal-directed behavior

Disturbance (d) : – Factors that affect the state of the plant

in ways that have not been or can not be, anticipated by system designer

Goal +

-

Error

Worker

Action

Plant

State

A complex model of goal-directed behavior

Output

Disturbance

A complex model of goal-directed behavior

관계식 – a=(g-d) / P

d 의 예측이 불가능하므로 , a 의 예측은 불가능

동일 목표를 위해 다른 행위 가능 , 같은 행위가 다른 시간에 다른 영향을 줌 – Context-conditioned variability (motor control)– Unanticipated variability (cognitive engineering)– Situated action (cognitive science)

Resolution(Closed/Open systems)

The more closed a system is, the more amenable it is to instruction-based forms of task analysis.

Open system gives rise to context-conditioned variability

Workers must adapt online in real time to disturbance that cannot possible be foreseen by analysts (Hirschhorn 1984).

참고문헌 : 사전에 예측불가 : Ujita, Kawano & Yoshimura, 1995)

Constraint-based approaches

Negative feedback models : constraint-based structure, not instruction-based

Discretion is not the same as complete freedom– Not advocating that workers be allowed to

do whatever they want– The discretion and flexibility that we

advocating is bounded by constraints.

An unresolved problem

Constraint-based task analysis can lead to new design functionality, making it more likely that productivity will be improved.

A particular goal to be achieved may not be identifiable beforehand : an unanticipated emergency in a nuclear power plant.– CBTA 의 한계 → Work Domain Analysis 로 극복

An unresolved problem

– How can we know what the goal should be?– To require workers to “Note any problems”

by Shepherd(1992)– It merely provides a place holder for what

workers are supposed to do– Little to identify the information or

knowledge that workers require to cope withEven constraint-based task analysis do

not provide a very satisfactory basis for dealing with unanticipated events.

Dealing with unanticipated events

Ex) Spatial navigation (Thorndyke and Goldin 1983)

– How people learned to find their way– Two types of spatial knowledge

• Procedural knowledge : sequence of actions• Survey knowledge ; spatial relationships between locat

ions and routes in an environment– Navigation aids

• Procedural knowledge can be embedded in directions• Survey knowledge can be embedded in a map

Dealing with unanticipated events

Directions Maps

Mental economy Efficient Effortful

Ability to adapt to unforeseen contingencies

Brittle Flexible

Scope of applicability Narrow Broad

Ability to recover from errors Limited Great

Direction 과 Map 의 장단점

Relevance to work analysis

Two forms of work analysis– Task representations (like directions)

• What goals they should achieve or how they should be achieving them

– Work domain representations (like maps)• To describe the structure of the controlled

systemTask VS Work domain

– Task : what workers do– Work domain : what workers do it on (i.e.,

the object of action)

★ Those familiar with computer programming

- Control structure : task

- Data structure : work domain

Task analysis VS Work domain analysis

Directions Maps

Mental economy Efficient Effortful

Ability to adapt to unforeseen contingencies

Brittle Flexible

Scope of applicability Narrow Broad

Ability to recover from errors Limited Great

SummaryMost existing task analysis techniques are not

very useful– Instruction based TA– Not suited for complex STS

• To underestimate context-conditioned variabilityConstrained based task analysis are better

suited for complex STS– Contribute in flexibility, productivity, worker health

and on-the-job training– But not capable of dealing with unanticipated events

Work Domain Analysis for unanticipated events

Work domain analysis + Constrained based task analysis