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Y Cathedral Bazaar and Bridge are competing Software Engineering

Metaphors

SERGSERGSoftware Engineering Research GroupSoftware Engineering Research Group

University of AucklandUniversity of Auckland

Presentation by Wolfgang Fahl, Presentation by Wolfgang Fahl, BITPlan2008-11-282008-11-28

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Agenda

Introduction: W. Fahl/BITPlan • What are Metaphors & Maxims?• Software Engineering Metaphors &

Maxims – a guided tour• Raffle• Summary & Conclusion• Discussion

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Wolfgang Fahl

• Wolfgang Fahl

• Computer ScientistRWTH Aachen, Germany

• President iSAQB

• CEO BITPlan

S M A R T S OL U T I N SO

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Agenda

• Introduction: W. Fahl/BITPlan What are Metaphors & Maxims?• Software Engineering Metaphors &

Maxims – a guided tour• Raffle• Summary & Conclusions• Discussion

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What is a Metaphor?

• describe one thing by using another thing (the metaphor) as a helping device to do so

• knowledge of implicit and explicit attributes of the metaphor is used to „transfer“ this knowledge to the target subject

• differences cause a dilemma – they can be useful if discussed and harmful if they are not recognized

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What is a Maxim?

• GuidelineNon mandatory streamline of particular processes according to a set routine

• MoralMessage conveyed or learned from a story or event

• MaximA principle or rule. A wise saying to advise a recommended course of conduct

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Agenda

• Introduction: W. Fahl/BITPlan • What are metaphors & guidelines?Software Engineering Metaphors &

Maxims – a guided tour• Raffle• Summary & Conclusions• Discussion

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SE Metaphors & Maxims

• It‘s broken anyway• Phaedrus‘s knife• Architecture• The Cathedral• Engineering• The Bridge• The Factory• The Y• The Bazaar

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It‘s broken anyway

• The software is broken anyway ...

• How can we make sure it doesn‘t harm anybody?

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Phaedrus‘s knife

What is Analysis?

Three methods of organization that pervade all human thinking:

2. Whole - Part

3. Groups – Members

1. Objects - Attributes

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COMPONENTS

MOTORCYCLE

FUNCTIONS

Phaedrus‘s knife:Analysis

• Model – a representation of the real world COMPONENTS

MOTORCYCLE

FUNCTIONS

POWER ASSEMBLY RUNNING ASSEMBLY• Model – a construction plan

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Architecture

• Loads

• Materials

• Style

• Purpose

• Optimization

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The Cathedral

„Have you drawn your plans, Tom Builder?“

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Castles: rough stones

• In the 10 th century buildings where created using rough stones, which were put together to thick walls using mortar.

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Gaps are filled manually

• The stones are unevenly shaped and the individually distributed mortar creates the connection between them.

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Cathedrals - cut stones

• Walls created from precisely cut stones are lighter and still more stable.

• This approach leads to higher, more beautiful and less costly* buildings

* it‘s possible to add more extra art and glass now

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Model, Planning, Style

• Before and during build time master builder and owner discuss details using models

• Planning leads to predictability and feasibility

• A style emerges

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The result speaks for itself

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Engineering

• What did the creators of the Eiffel tower know about the finished tower at the time when this picture was taken?

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Too much of a good thing

• The Forth Bridge is overdesigned since the builders could not exactly tell how much material was necessary for a long term safe and reliable operation

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The Bridge

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The Bridge

Bridge between

man and

computerHumans Machine© BITPlan, 2000expected delivered

asked for

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The abstraction trap

More abstraction

does not lead to

closing the gap

between humans

and the computer

Machine

-

-

-

-

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IdeasWishesExpectationsFeelings

Bits und

Bytes

Humans

Binary code

Assembler

ProceduralLanguages

objekt orientedLanguages

ModelLanguages

Meta-Languages

Meta-Meta-Languages

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The Factory

• Mass production

• Lean production

• Quality control

• Built-to-order

• Service centered selling

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Domain specificRequirements

TechnicalRequirements

DomainModel

ArchitectureModel

Mapping rules

ImplementationDomain code uses architecture code

The Y-Principle

PIM PDescM

PSM (only implicit)

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The Bazaar

• The Cathedral & the BazaarThe Linux success

• Homesteading the Nusphereproperty and ownership customs of the OSS community

• The magic cauldron Tragedy of the commons – the inverse commonsOSS economy

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Agenda:Raffle

•Introduction: W. Fahl/BITPlan

•What are metaphors & guidelines?

•Software Engineering Metaphors & Maxims – a guided tour

Raffle

•Summary & Conclusions

•Discussion

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Agenda

• Introduction: W. Fahl/BITPlan • What are metaphors & guidelines?• Software Engineering Metaphors &

Guidelines – a guided tour• RaffleSummary & Conclusions• Discussion

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Summary

• Shift towards Architecture / Engineering• Models as balance of analysis result &

construction plan• „Real world“ projects don‘t seem to fit the

methapors (yet?)• Metaphors are a common approach to

describe complex interactions (Jazz-Band/Orchestra, ... Lego, ...)

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Conclusions

• Decision making is the key process in software engineering

• The shown Maxims and Metaphors give an idea for possible decision making approaches

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Agenda

• Introduction: W. Fahl/BITPlan

• What are metaphors & guidelines?• Software Engineering Metaphors &

Maxims – a guided tour• Summary & ConclusionsDiscussion

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