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INTRODUCING THE CAPTURE OF ARGUMENTATION-BASED

DESIGN RATIONALE INTO INDUSTRIAL PRACTISE

Rob BracewellKen Wallace

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The Design Rationale editor (DRed)

• What is DRed?• Where did it come from?• How was it researched, implemented

and introduced?• Why do designers seem to find it a

help rather than a hindrance?

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What is DRed?

• DR capture tool used by aerospace designers on live tasks from v0.1 onward– just 3 weeks’ software development in v0.1

• Example: Dave Williams, July 2002– ANTLE Internal Gear Box– Issue: how to improve scavenge while

avoiding oil leaks?– Rationale shown in recent DRed, but was

originally captured with crude early version

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Issue: Open

Start with an open issue

Note “traffic light” statuses

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No hidden information, easy to scan and browse

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Proposed answers: Open

Development of answers and arguments

Pro argument Con argument (qualified)

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Argument declared to be false

All elements have alternative statuses, easily changed

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Answer rejected in response to dominant con

Changes of status capture decisions

Follow arrows for knock-on effects

Rejection decisions captured

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Tunnel links enable large, connected rationales to be distributed legibly

Mouth of “tunnel” carrying link into a new file

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Far end of tunnel

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Back to previous graph

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Where did it come from?

DesignRationaleManager

ExpertiseFinder

Productworld

Processworld

Design reviewmeetings

IndividualDesigners

Communitiesof Practice

TECHNICALSYSTEM

OtherSystem

OtherSystem

KCSR Project: Socio-Technical Approach to Engineering KM

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Where did it come from?

DesignRationaleManager

ExpertiseFinder

Productworld

Processworld

Design reviewmeetings

IndividualDesigners

Communitiesof Practice

TECHNICALSYSTEM

OtherSystem

OtherSystem

KCSR Project: Socio-Technical Approach to Engineering KM

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Need for Design Rationale Capture

• By 2001, rationale capture had become moribund topic in design research community– Full text search of proceedings of premier

annual design research conference (ASME DETC) revealed just 3 citations of IBIS or derivative work in 4 years

– IBIS community had shifted focus toward facilitated capture of real or virtual meetings

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Example of gIBIS

Figure 3: an Example of gIBIS [Buckingham Shum, 1991]

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DRL: a rather complex notation

Figure 11: DRL notation [Buckingham Shum, 91]

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Commercial Tool (2001): QuestMap

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Commercial Tool (2001): DRAMA

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Rolls-Royce Design Definition Report

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Design Definition Report Study

• Objectives– Inform development of the KCSR project Design

Rationale Manager– Explore the potential uses and benefits of simple

graph-based design rationale notations in design processes.

– Explore the best structure for textual design reports• Use of “Graphlet” graph layout & editing tool

– produced by University of Passau– efficient, robust, underlying graph processing library

(C++) with flexible scripted GUI (Tcl/Tk)

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Design Definition Report Structure

• 1. Summary• 2. Problem Analysis/ Requirements Specification

– 2.1 …• 3. Alternative Solutions

– 3.1 …• 4. Final Solution Description

– 4.1 …

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Initial DR Notation

• Directed graph of these elements:

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DKC118351: Problem 1

• During strip of the Trent 500 development engine 70003/2 is was found that two anti score plate tangs with balance weights were missing of the HPT rotor assembly

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DKC118351: Problem 2

• Problems were experienced during the build of the HPT rotor for development engine 70004/1 during the straight line build procedure (RTS81338). Swash and runout measurements were not repeatable once the main tooling bolts were removed from the assembly and the coverplate was only held on by the set screws

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Conclusions of DDR study

• Subjective impression favourable, in that:– use of notation not difficult, feels natural– improves structure of DR captured compared to

textual design definition reports– graphical portrayal easier to interpret than original

structured text document– may help in structuring, representing and

reviewing designers’ thought processes• Promising enough to be tested by designers

on live problems

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Initial Development of DRed tool

• Simplified version of Graphlet, customised for DR by Tcl/Tk scripting

• Standalone, file based, Win98/NT/2000 platforms• Export DR graphs to .wmf for Word/PowerPoint• First version delivered in under a month to

interested parties at RR for trials of the DR notation• Research ideas, user suggestions and feedback on

problems rapidly transformed into working software• 8 releases to core evaluation team in 8 months

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Questionnaire of users in Rolls-Royce after 6 month trial

• Found to be easy to use – 14 out of 19 responses found easy or very easy

• Some immediate improvements to design process:– 10 out of 10 found improved or slightly improved overall view of

design process– 7 out of 10 found improved or slightly improved keeping track of

design process– 6 out of 10 found improved or slightly improved evaluating and

deciding between concepts– No (!) negative feedback, 0 out of 10 said hindered/slightly hindered

design process

• Designers perceive future benefits. Main benefits:– communicating to others 11 out of 14 designers– monitoring progress 9 out of 14 designers

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Examples of use in Rolls-Royce

• Encouraging clear and rigorous thinking– Industrial Trent 60 dual fuel

A “eureka” moment resulting from a DRed analysis caused the team to change design concept to “a rationalised, cost effective layout where liquid manifolds are protected from radiation, and are clear of the flame break-out region”; Allan Salt, Preliminary Design, Ansty

– JSF passive valve/rear casing clash and JSF Z ring design; both Martin Cullen, Bristol

– iRB211 Dual Fuel DLE Deletion of Central Diffusion Gas Circuit“DRed was used to clearly identify the problem, the various solutions and their advantages and disadvantages. … was successful due to its: clarity, rapidity [and] colour coded visual symbols”; Yasmine Ghaly & Richard Hamby, Montreal

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Examples of use in Rolls-Royce

• Structuring and clarifying complex problems– Design combines problem understanding and solution

creation…

– Edelweiss failure investigation and subsequent design; Ian Merryfield & Paul Brooks, Derby“An added … bonus was that [DRed] provided an admirable diagnostic tool which has been used successfully to understand Civil Aerospace fleet events.” Geoff Kirk, Chief Design Engineer

– Adour LPT blade rubs root cause; Keith Nurney, Bristol

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Examples of use in Rolls-Royce

• Communicating in reviews – JSF mandates DRed use in Scheme Reviews

Andy Haasz– Submarines Main Coolant Pump rundown problem

in review with the Navy, Andy Storer– 1) Solution to EJ200 bearing stub shaft damage

on LPT installation. 2) Assessment of squeeze film options to reduce EJ200 vibration - both examples Volker Herzog, Bristol“Volker used DRed in a DDRAM presentation to good effect. It gave a very clear picture of the thought processes and reasons for choosing the final solution. For the CDE, it provided a visible route map which aided discussion of alternative solutions and agreement of the chosen solution.”Graham Slack D(A)

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Examples of use in Rolls-Royce

• Communicating to the team, focussing effort– Trent 500 fir tree cracking; Richard Corran– Trent 1000 combustor design; Giles Harvey, APSD

• Saves effort in creating reports– Accepted by the Design Practices Committee– Trent 1000 IP/HP Coupling & presentation to ANA

“DRed proved to be a powerful tool when considering the complex issues surrounding the many concept options…. It … enabled rational down select of the leading designs. This has proven tobe a valuable reference pack throughout the design evolution”Andy Swift, APSD

• Use by supply chain and to support review of designs done for R-R– Use of DRed in India by Quest

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Why is DRed an effective design tool?

• Simplicity, low training requirements• No database management system required

– Tunnel linked DRed files live in the project folder– Simple to deploy DRed and create a browsable and

searchable archive of completed project folders• Easy to produce comprehensive hardcopy identical

to view on screen – no hidden information• Traffic-light statuses of all elements• Anchor links to locations in graphical elements• Tunnel linking more effective for expressing design

dependencies than transclusion?