book

Object Design: Roles, Responsibilities, and Collaborations

Name: Object Design: Roles, Responsibilities, and Collaborations
ISBN: 0201379430

by Rebecca Wirfs-Brock, Alan McKean

November 2002

Intermediate to advanced

416 pages

10h 19m

English

Addison-Wesley Professional

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Copyright
Foreword
Foreword
Preface
How To Read This BookAcknowledgmentsRebecca’s AcknowledgmentsAlan’s Acknowledgments
1. Design Concepts
Object MachineryRolesObject Role StereotypesRoles, Responsibilities, and CollaborationsObject ContractsConditions-of-Use and Aftereffect GuaranteesDomain ObjectsApplication-Specific ObjectsInterfacesClassesTwo RolesCompositionInheritanceObject OrganizationsComponentsPatternsApplying Double Dispatch to a Specific ProblemA SolutionA Better SolutionThe Double Dispatch PatternThe Real Benefits of Using PatternsFrameworks, Inc.ArchitectureArchitectural StylesCentralized Control StyleDispersed Control: No CentersDelegated ControlExamining Interactions: A Layered Architecture ExampleLocating Objects in LayersDesign DescriptionSummaryFurther Reading
2. Responsibility-Driven Design
A Process for Seeing, Describing, and DesigningLaunching the Production: Project Definition and PlanningSetting the Stage: Early DescriptionStaging the Production: Design“Seeing” from Multiple PerspectivesWriting the Script: Analysis DescriptionsUsage DescriptionsActors and Their View of Our SystemUse CasesA Word Processor ExampleScenariosConversationsAdding DetailAlternatives, Annotations, and Other SpecificationsExceptional ActionsBusiness and Application PoliciesDesign NotesOther SpecificationsGlossariesConceptual ObjectsConcentrating on the CoreDocumentPageParagraphSpell CheckerCasting the Characters: Exploratory DesignCRC CardsInventions: Using PatternsPursuing a SolutionBouncing Between Ideas and DetailsTuning the Production: Design RefinementDetermining Collaboration and Control StylesDesigning to Support User VariationsDesigning for Flexibility and ExtensionDesigning for ReliabilityMaking Our Design Predictable, Consistent, and ComprehensibleSummaryFurther Reading
3. Finding Objects
A Discovery StrategyLooking for Objects and Roles, and Then ClassesWhy Tell a Design Story?Search StrategiesWhat’s in a Name?Describing CandidatesCharacterizing CandidatesConnecting CandidatesLooking for Common GroundDefend Candidates and Look for OthersSUMMARYFURTHER READING
4. Responsibilities
What Are Responsibilities?Where Do Responsibilities Come From?Strategies for Assigning ResponsibilitiesRecording ResponsibilitiesMaking Initial AssignmentsGetting UnstuckImplementing Objects and ResponsibilitiesAn Object Can Play Multiple RolesDesigning Methods and Signatures That Support ResponsibilitiesTesting Your Candidates’ QualitySummaryFurther Reading
5. Collaborations
What Is Object Collaboration?Preparing for CollaborationRecording Candidate CollaborationsThe Design Story for the Speak for Me SoftwareCollaboration OptionsWho’s In Control?How Much Should Objects Trust One Another?Strategies for Identifying CollaborationsLooking at an Individual Object’s Role: Stereotypes Imply CollaborationsInformation HoldersStructurersService-ProvidersControllersCoordinatorsInterfacersLooking at Individual Responsibilities: They Imply CollaborationsDesigning the Details of a Complex ResponsibilityDesigning Collaborations for a Specific TaskIdentifying Applicable PatternsIdentifying How Architecture Influences CollaborationsSolving Problems in CollaborationsSimulating CollaborationsPlanning a SimulationRunning a SimulationDesigning Good CollaborationsThe Law of Demeter: A Case StudyMaking Collaborations PossibleGuidelines for Making ConnectionsDesigning Reliable CollaborationsWhen Are We Finished?SummaryFurther Reading
6. Control Style
What Is Control Style?COntrol Style OptionsMaking Trade-OffsCentralizing ControlDelegating ControlThe Limits of Control DecisionsDeveloping Control CentersA Case Study: Control Style for External User EventsCentralizing Control in the MessageBuilderRefactoring Decision Making into Small ControllersRefactoring Decision Making into State Methods within the MessageBuilderAbstracting Away DecisionsDelegating More ResponsibilityDesigning the Control Style for the Guessing NeighborhoodDesigning a Similar Control Center: Can We Be Consistent?Summary

7. Describing Collaborations
Telling Collaboration StoriesA Strategy for Developing a Collaboration StoryEstablishing Scope, Depth, and ToneListing What You Will CoverDeciding on the Level of DetailShowing a Bird’s-Eye ViewShowing Collaborators OnlyShowing a Sequence of Interactions Among CollaboratorsShowing an In-Depth ViewShowing a Focused InteractionShowing an Implementation ViewShowing How to Adapt a CollaborationWhere UML Diagrams Fall ShortChoosing the Appropriate FormTell It, Draw It, Describe It: GuidelinesOrganizing Your WorkAdding EmphasisUnfolding Your StoryUnderstanding What’s FundamentalPutting It All TogetherPreserving StoriesSummaryFurther Reading
8. Reliable Collaborations
Understanding the Consequences of FailureIncreasing Your System’s ReliabilityDetermining Where Collaborations Can Be TrustedTrusted Versus Untrusted CollaborationsImplications of TrustIdentifying Collaborations To Be Made ReliableWhat Use Cases Tell UsDistinguish Between Exceptions and ErrorsObject Exceptions Versus Use Case ExceptionsObject Exception BasicsException- and Error-Handling StrategiesDetermining Who Should Take ActionAsking the Client to Check Before Making a RequestGiving the Client Some Responsibility for RecoveryGiving the Service Provider Some Responsibility for RecoveryDesigning A SolutionBrainstorm Exception ConditionsLimit Your ScopeRecord Exception-Handling PoliciesDocumenting Your Exception-Handling DesignsSpecifying Formal ContractsReviewing Your DesignSummaryFurther Reading
9. Flexibility
What Does It Mean to Be Flexible?Degrees of FlexibilityThe Consequences of a Flexible SolutionNailing Down Flexibility RequirementsRecording VariationsVariations and RealizationsIdentifying the Impact of a VariationExploring Strategies for Realizing FlexibilityUsing Templates and Hooks to Support VariationsThe Role of Patterns in Flexible DesignsVarying an Object’s Behavior with the Strategy PatternHiding Interacting Objects with MediatorMaking a Predefined Object or System Fit Using AdapterHow Do Patterns Increase Flexibility?How to Document a Flexible DesignConsider Your AudienceDescribing How to Make a VariationChanging a Working System’s DesignSummaryFurther Reading
10. On Design
The Nature of Software DesignTackling Core Design ProblemsFrame the ProblemDealing with Revealing Design ProblemsA Story About Managing Shared InformationA Story About Connection Problem ComplexityA Story About a Design Problem That Never Got EasierCan Revealing Problems Be Wicked, Too?Strategies for Solving Revealing ProblemsRedefining the ProblemSynthesizing a SolutionWorking on the RestDesigning ResponsiblyFurther Reading
Bibliography

Content preview from Object Design: Roles, Responsibilities, and Collaborations

Chapter 4. Responsibilities

Christopher Alexander states, “Form is part of the world over which we have control, and which we decide to shape while leaving the rest of the world as it is.” The measure of a design’s goodness is how well the form fits into its context. When we shape an object’s responsibilities, we are inventing a form that should fit smoothly into its environment. We have the luxury of shaping both form and context when we distribute responsibilities among collaborators.

The rightness of a form, according to Alexander, depends on how effortlessly it contacts with its environment. To make informed decisions about an object’s responsibilities, we should divide form and context across several dimensions and consider several aspects ...

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Object Design: Roles, Responsibilities, and Collaborations

by Rebecca Wirfs-Brock, Alan McKean

Chapter 4. Responsibilities

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