Robert Biddle Carleton University Canada

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Robert BiddleCarleton UniversityCanada
ExtremeSystem
ProgrammingMetaphor
Rilla Khaled, Pippin Barr James NobleVictoria
University of WellingtonNew Zealand
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Outline

• XP System Metaphor
• Peircian Semiotics
• Modeling Metaphor
• XP Practice
• Choosing a Metaphor
• Evaluating a Metaphor

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Agile Software Development

• Individuals and interactionsover processes and
  tools
• Working software over comprehensive
  documentation
• Customer collaboration over contract negotiation
  
• Responding to changeover following a plan

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BeckXP eXtreme Programming

• Fine scale feedback
• TestDrivenDevelopment (were UnitTests
  AcceptanceTests)
• PlanningGame
• WholeTeam (was OnsiteCustomer)
• PairProgramming
• Continuous process rather than batch
• ContinuousIntegration
• DesignImprovement (was RefactorMercilessly)
• SmallReleases
• Shared understanding
• SimpleDesign
• SystemMetaphor
• CollectiveCodeOwnership
• CodingStandard or CodingConventions
• Programmer welfare
• SustainablePace (original name FortyHourWeek)

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XP System Metaphor

• A story that everyone - customers, programmers
  and manager - can tell about how the system work.
  Beck
• The metaphor just helps everyone on the project
  understand the basic elements and their
  relationships. Words chosen to identify technical
  entities should be consistently taken from the
  chosen metaphor. As development proceeds and the
  metaphor matures, the whole team will find new
  inspiration from examining the metaphor. Beck
• The team had the benefit of a very rich domain
  model developed by members of the team in the
  project's first iteration. It gave the members of
  the project an edge in understanding an extremely
  complex domain. C3 Team
• I still haven't got the hang of this metaphor
  thing. I saw it work, and work well, on the C3
  project, but it doesn't mean I have any idea how
  to do it, let alone how to explain how to do it.
  Fowler

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Basic Peircean Semiotics

• Semiotics is the study of signs.
• Charles Sanders Peirce developed a triadic model
  of the sign
• Object (or Referent)
• the concept or thing actually represented by the
  sign.
• Representamen the sign itself.
• Interpretant the result of an interpreters
  encounter with a sign.

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Unlimited Semiosis
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Ecos Model Reader
To make his text communicative, the author has to
assume that the ensemble of codes he relies upon
is the same as that shared by his possible
reader. The author has thus to foresee a model of
the possible reader (hereafter Model Reader)
supposedly able to deal interpretatively with the
expressions in the same way as the author deals
generatively with them. Umberto Eco The Role
of the Reader, 1979
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A Semiotic Model of MetaphorPierce, Lakoff
Johnson
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Modeling MetaphorMetaphor Introduction
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Modeling MetaphorMetaphorical Entailment
A Metaphor is a Sign Generator
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Entailment Linkage
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XP System Metaphor
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OOP Signs
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Modeling MetaphorProgram Code Signs
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• XP
• System
• Metaphor
• Model

MetaphorIntroduction
MetaphoricalEntailment
ProgramCode
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Practice Finding and EvaluatingMetaphorscape
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A Bank Account is a Water Reservoir
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MetaphorscapeChoosing a Metaphor
Metaphor Introduction

• Brainstorming Potential Metaphors
• With referent, suggest representamen
• Include team, customer, domain expert
• Consider explaining system to non-expert
• Consider surrounding metaphors
• Select most promising n

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Choosing a Metaphor II

• Brainstorming Metaphorical Entailments
• Choose metaphor
• Identify entailments referent and interpretant
• Begin individually and then merge

Metaphorical Entailments
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Choosing a Metaphor III

• Brainstorming Program Code Signs
• Identify implied objects/classes
• Determine usefulness of objects/classes
• Correctness, consistency, coherence
• Select useful, discard others

Program Code
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Conclusion

• Beck A story that everyone - customers,
  programmers and manager - can tell about how the
  system work.
• Fowler This is a real gap in XP, and one that
  the XPers need to sort out.
• Our explorations
• Language Vocabulary and Structure
• Techniques Based on OOD and HCI practice

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Robert BiddleCarleton UniversityCanada
ExtremeSystem
ProgrammingMetaphor
Rilla Khaled, Pippin Barr James NobleVictoria
University of WellingtonNew Zealand
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(No Transcript)
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System Ideas

• Web browser
• Web server
• E-commerce site
• Email client
• Space Invaders
• GPS handheld
• Blog software

• Payroll system
• Compiler
• Banking system
• Library
• Backup system
• PDA software
• CVS

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(No Transcript)
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User-Interface Metaphor
You can take advantage of people's knowledge of
the world around them by using metaphors to
convey concepts and features of your application.
Use metaphors involving concrete, familiar ideas
and make the metaphors plain, so that users have
a set of expectations to apply to computer
environments. (Apple Computer Inc., 1992)
Familiar metaphors provide a direct and
intuitive interface to user tasks. By allowing
users to transfer their knowledge and experience,
metaphors make it easier to predict and learn the
behaviors of software-based representations.
(Microsoft Corporation, 1995)
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The Document Metaphor
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Metaphor and Metaphorical Entailments

• The data is an object.
• The data can be written on.
• The data can be read.
• The data contains text, and possibly images and
  graphs, etc.
• The data can be ripped.
• The data can be typed up.
• The data is usually on white paper.
• The data can be photocopied.
• The data can be written in pencil or pen or ink.
• The data can (sometimes) be edited using twink or
  an eraser.
• The data contains information.
• The data can be set on fire.
• The data can be picked up and moved from place to
  place.
• The data can be thrown in a trashcan.
• The data can give you a paper-cut.

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XP System Metaphor

• A story that everyone - customers, programmers
  and manager - can tell about how the system work.
  Beck
• The metaphor just helps everyone on the project
  understand the basic elements and their
  relationships. Words chosen to identify technical
  entities should be consistently taken from the
  chosen metaphor. As development proceeds and the
  metaphor matures, the whole team will find new
  inspiration from examining the metaphor. Beck
• The team had the benefit of a very rich domain
  model developed by members of the team in the
  project's first iteration. It gave the members of
  the project an edge in understanding an extremely
  complex domain. C3 Team
• I still haven't got the hang of this metaphor
  thing. I saw it work, and work well, on the C3
  project, but it doesn't mean I have any idea how
  to do it, let alone how to explain how to do it.
  Fowler

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Evaluating a Metaphor

• How is the Metaphor Good?
• whether the entailments of the metaphor contain
  programmable ideas
• whether the metaphor addresses the major system
  components and their known functionality.
• whether the metaphor entailments provide a
  vocabulary with which to describe the system
• Is the metaphor too poor?
• which system components and interactions are left
  undescribed by the metaphor
• Is the metaphor misleading?
• whether the metaphorical entailments imply
  non-existent system components or non-existent
  behaviour.