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SY DE 542

Work Domain Analysis (cont’d)Information Requirements

Jan. 17, 2005

R. ChowEmail: chow@mie.utoronto.ca

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WDA: Defining the System• What does the user want to control?• What does the user want information on?

Main: - Troubleshooting by User

- Make Visible to Uservs.

Peripheral:- Troubleshooting by Other - Make Transparent to User

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Example: Power Generation & Delivery

• Countrywide:– Plants, Electrical Grid, Energy Users

• Plant:– Units, Storage, Internal Grid

• Unit:– Generator, Turbines, etc.

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WDA: System Boundary

• What to Include (Usually):– Things user can control, wholly or partly– Things that interact with user’s work domain– Things the user must monitor or supervise

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WDA: System Boundary

• What to Exclude (Usually):– Databases– Sensors– Input and Output Devices– Human-Computer Interface– Software– Object of Design or Redesign

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WDA: Part-Whole Hierarchy• Decomposition of a system into

subsystems, and subsystems into components … (from coarse -> fine)

• # of levels is not fixed

• A complete WDA has 2 dimensions:– Abstraction Hierarchy (along vertical)– Part-Whole Hierarchy (along horizontal)

• Not every cell in this 2-dimensional space will be filled

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A Generic WDA

System Subsystem Component

FunctionalPurpose

Abstract

Function

Generalized

Function

Physical Function

Physical

Form

Part-Whole HierarchyA

bstr

actio

n H

iera

rchy

finecoarse

concrete/physical

abstract/functional

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Two-Dimensional WDA

• Functional Purpose is generally associated with whole system

• Physical Function is generally associated with individual components

• Some representation at every level of each hierarchy

• But no fixed number of cells to complete

• May help to distinguish AND vs. OR

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DURESS Example (revisited)– 1 Water Source (temp fixed @ 10 deg C)– 2 Reservoirs

• If overfilled, system shuts down– 2 Heaters

• Each unique to a single reservoir• If an empty reservoir is heated, system blows up

– 2 Redundant Feedwater Streams per Reservoir • Fws-A1 & Fws-B1; Fws-A2 & Fws-B2

– Pumps: ON / OFF– Valves:

• Primary Input (VA & VB): 1-10• Secondary Input (VA1, VA2, VB1, VB2): 1-10• Output (VO1, VO2): 1-20

– Demanded Temperatures (constant):• 40 deg C for Res1; 20 deg C for Res2

– Demanded Supplies (dynamic):• Same or different for Res 1 and Res 2

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Functional Purpose• What was the work domain designed to do?• How do I know if it’s working correctly? • How do I know if it’s working well vs. poorly?

Some checks:• Have I found at least two purposes?• What else is important besides performance?

safety, efficiency, environment, profit?• Do my purposes hold across all possible tasks?

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DURESS: Functional Purpose

• Temperature Goal

• Output Goal

• Temp1, Temp2, Output1, Output2

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Abstract Function

• What laws cannot be broken?

• What priorities must be achieved?

• What flows through the system? What is conserved?– Mass, Energy, Information, Money,

Unchangeable Resources

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DURESS: Abstract Function

• Mass1, Mass2• Energy1, Energy2• How do you know when mass is conserved

(or not)?– Mass Source, Inventory, Sink– When conserved, what is relationship?– When not conserved, what is relationship?

• Likewise for energy:– Energy Source, Inventory, Sink

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Generalized Function• How are causal relationships implemented?• How are flows, conversions implemented?• Some processes to consider:

– combustion, convection, radiation, conduction, evaporation, condensation, distillation, cracking, moving, launching, digestion, respiration (Hint: -ing; -ion)

• What processes must user monitor?• NOT what processes must user do with interface!

– e.g., monitoring, detecting, managing, reporting

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DURESS: Generalized Function• Mass is implemented as WATER• Energy is implemented as HEAT• Subsystem Level:

– Heat and Water Injection– Water Holding System– Heat Holding System– Heat Transfer System– Heat and Water Removal

• Component Level– Pump Flow, Valve Flow– Water Holding Tank– Heat Holding Tank– Heat Transfer– Valve Flow

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Physical Function

• What are the components?

• What are their capabilities?

• How are they involved in the processes?

• (Hint: capabilities usually have limits)

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DURESS: Physical Function• Pumps (PA, PB)

– Capability: On / Off

• Input Valves (VA, VB, VA1, VA2, VB1, VB2)

– Capability: 0-10 units/time

• Reservoirs (R1, R2)

– Capability: 1-100 units; 0-100 deg C

• Heaters (H1, H2)– Capability: 0-10 setting

• Output Valves (VO1, VO2)– Capability: 0-20 units/time

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DURESS: Physical Form

• Location and Appearance of:– PA, PB, VA, VB, VA1, VB1, VA2, VB2, VO1,

VO2, R1, R2, H1, H2

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Physical Form• What does the work domain look like?• What are the sizes, locations, colours, shapes,

locations, conditions, materials of the components?

• Not every attribute of every component needs to be included – think about how info will be used!

• Potential Uses– Icon– Video– Detailed Drawings– Layout and Connections

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WDA: Recommended Approach• Define the System• Start from Top of AH

– >= 2 purposes?– evaluation criteria?

• Next, work from Bottom – All available resources and equipment?– Form and Function?– No interface? No controller?

• Complete Middle– AF: causal laws, conservation principles– GF: more concrete processes

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WDA: Important Checks• Check Connections:

– All boxes connected Up AND Down?– Unconnected = something missing, extra, or in wrong

place

• Check Language:– Unique to each level?

• Check for Means-Ends Relationships– Confusions with Membership? (similar function in

different part of system or exact same function?)– Confusions with Part-Whole? (belong to same

subsystem with given function or serve same function themselves)

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Means-End Links:Some Counter-Examples

Pump Valves Mass Source 1

PA PB VA1,VA2,VB1,VB2 Water Water

Input 1 Input 2

Water Input 1Water Input 1

PA VA VA1 VA2 PA VA VA1 VB1

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Part-Whole vs. Means-Ends

Water Input B1

Water Input A1

MassSource

1

AF

GF

PFuncPump

AValve

A

PumpFlow

A

ValveFlow

A

ValveFlow

A1

ValveA1

PumpB

ValveB

ValveB1

PumpFlow

B

ValveFlow

B

ValveFlow

B1

Subsystem Components

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Information Requirements

• Convert AH into a list of variables

• Extract level-by-level

• Start at top with Functional Purpose

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Functional Purpose

• Measures of System Performance

• Can also be measures of– Safety– Environmental Impact – Profitability ($)– Efficiency (%)

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Abstract Function• Measures of:

– Mass– Energy– Momentum– Force– Power– Torque– Information

• (Rates of) Input, (Rates of) Output, Storage

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Generalized Function

• Temperature

• Pressure

• Volume

• Velocity

• Acceleration

• Other process measures …

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Physical Function

• Level

• % open or closed

Consider settings and possible states …

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Physical Form

• Colour

• Shape

• Size

• Length, width, depth

• Location

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Information Availability

• For each variable, determine if it is:– Currently Available

• Directly sensed?• Calculated from sensor data?

– Currently Unavailable• Can be sensed?• Can be calculated from sensor data?(If so, will sensor be added?)• Cannot be sensed or calculated?(May be possible in future)

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Information Availability Table

• Currently sensed

• Currently calculated

• Will be calculated – requirements?

• Will be sensed

• Will not be sensed/calculated – solution?