Patterns and AntiPatterns

Patterns and AntiPatternsPatterns and AntiPatterns

Ku-Yaw ChangKu-Yaw [email protected]@mail.dyu.edu.tw

Assistant Professor, Department of Assistant Professor, Department of Computer Science and Information EngineeringComputer Science and Information Engineering

Da-Yeh UniversityDa-Yeh University

mailto:[email protected]

222004/05/212004/05/21 Patterns and AntiPatternsPatterns and AntiPatterns

OutlineOutline

BackgroundBackground Structured v.s. Object-Oriented ParadigmStructured v.s. Object-Oriented Paradigm

PatternsPatterns CommandCommand

AntiPatternsAntiPatterns BLOBBLOB

SummarySummaryReferencesReferences


BackgroundBackground

ParadigmParadigmA way of organizing system A way of organizing system abstractionsabstractions around properties of around properties of commonalitycommonality and and variationvariation..



ParadigmParadigmAbstractionAbstraction To focus on the general andTo focus on the general and

put aside the specific. put aside the specific. To emphasize what is common and To emphasize what is common and

deemphasize details deemphasize details



ParadigmParadigmCommonalityCommonality The Essence of AbstractionThe Essence of Abstraction To search for common elements that helps us To search for common elements that helps us

understand how family members are the understand how family members are the same.same.

VariabilityVariability The Spice of AbstractionThe Spice of Abstraction Being monotonous without variability.Being monotonous without variability.



ParadigmParadigmA way of organizing system A way of organizing system abstractionsabstractions around properties of around properties of commonalitycommonality and and variationvariation.. CommonalityCommonality

The backbone and skeleton of designThe backbone and skeleton of design VariabilityVariability

The flesh and bloodThe flesh and blood



ParadigmParadigmBefore 1975Before 1975 No specific techniquesNo specific techniques

1975 – 19851975 – 1985 Structured ParadigmStructured Paradigm

Functional DecompositionFunctional Decomposition

1985 – 20041985 – 2004 Object-Oriented ParadigmObject-Oriented Paradigm


Structured v.s.Structured v.s.Object-Oriented ParadigmObject-Oriented Paradigm

accountbalance

withdrawdeposit

determinebalance

accountbalance

deposit withdraw

determinebalance

message

message message



True Object OrientationTrue Object OrientationAlan ShallowayAlan Shalloway The objects in my code were well-formed and The objects in my code were well-formed and

tightly encapsulated. I could design excellent tightly encapsulated. I could design excellent data abstractions for inheritance hierarchies. I data abstractions for inheritance hierarchies. I thought I knew object-orientation.thought I knew object-orientation.

Now, looking back, I see that I really did not Now, looking back, I see that I really did not understand understand the full capabilitiesthe full capabilities of object- of object-oriented design.oriented design.

I know there was a better design.I know there was a better design.I just couldn’t see it.I just couldn’t see it.


PatternsPatterns

Having roots in the architecture field by Having roots in the architecture field by Christopher AlexanderChristopher Alexander

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PatternsPatterns

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PatternsPatterns

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PatternsPatterns

Expert behaviorExpert behavior do not try to find the solution from first principlesdo not try to find the solution from first principles reuse the essence of a proven solution to solve the reuse the essence of a proven solution to solve the

new problemnew problem


PatternsPatterns

Being applied to the software development Being applied to the software development successfully, especially in the object-oriented successfully, especially in the object-oriented communitycommunitySoftware reuseSoftware reuse Code reuse Code reuse Design reuseDesign reuse

the value of design experiencethe value of design experienceLayers : OSI 7-Layer ModelLayers : OSI 7-Layer Model


What is a Pattern?What is a Pattern?

Christopher AlexanderChristopher Alexander Each pattern describes a Each pattern describes a problemproblem which occurs over which occurs over

and over again in our environment, and then and over again in our environment, and then describes the core of the describes the core of the solutionsolution to that problem, in to that problem, in such a way that you can use this solution a million such a way that you can use this solution a million times over, without ever doing it the same way twice.times over, without ever doing it the same way twice.

Be applied in developing software in 1987.Be applied in developing software in 1987.Enter the mainstream of OO community in Enter the mainstream of OO community in 1994(1st PLoP)1994(1st PLoP)


PLoP ConferencesPLoP Conferences

Pattern Languages of ProgramPattern Languages of Program PLoPPLoP Chili PLoPChili PLoP Euro PLoPEuro PLoP Koala PLoPKoala PLoP Mensore PLoPMensore PLoP SugarLoaf PLoPSugarLoaf PLoP Viking PLoPViking PLoP OOPSLAOOPSLA ECOOPECOOP

Allerton Park


PatternsPatterns What is a Pattern?What is a Pattern?

Four Essential ElementsFour Essential Elements pattern namepattern name

easier to think and to communicateeasier to think and to communicate problemproblem

explain the problem and its contextexplain the problem and its contextdescribe when to applydescribe when to apply

solutionsolutiondescribe the elementsdescribe the elementstheir relationships, responsibilities, and collaborationstheir relationships, responsibilities, and collaborations

consequenceconsequenceresults and trade-offsresults and trade-offs


Pattern ExamplePattern Example

Pattern NamePattern Name CommandCommand

Pattern ProblemPattern Problem different requestdifferent request queue or log requestqueue or log request support undoable operationssupport undoable operations



Solution Solution (UML)(UML)



ConsequencesConsequences Decouples the object that invokes the Decouples the object that invokes the

operation from the one that knows how to operation from the one that knows how to perform it.perform it.

Commands can be manipulated and extended Commands can be manipulated and extended like any other object.like any other object.

Assemble commands into a composite Assemble commands into a composite command.command.

Easy to add new Commands. You don’t have Easy to add new Commands. You don’t have to change existing classes.to change existing classes.


Non-software Pattern ExampleNon-software Pattern Example

SolutionSolution


GoF - 94GoF - 94CreationalCreational Patterns Patterns

Abstract FactoryAbstract Factory SingletonSingleton

StructuralStructural Patterns Patterns DecoratorDecorator

BehavioralBehavioral Patterns Patterns CommandCommand

Pattern CategoriesPattern Categories


POSA (Vol. One) - 96POSA (Vol. One) - 96ArchitecturalArchitectural

MVC / Doc-ViewMVC / Doc-View BrokerBroker

DesignDesign ProxyProxy

IdiomsIdioms



POSA (Vol. Two) - 2000POSA (Vol. Two) - 2000Service Access and Service Access and Configuration Configuration Event HandlingEvent HandlingSynchronizationSynchronizationConcurrencyConcurrency



Obsessive use of 1 patternObsessive use of 1 pattern

There are more than There are more than 160160 fundamental fundamental patterns:patterns: 23 Gamma Patterns23 Gamma Patterns 33 Buschmann Patterns (16+17)33 Buschmann Patterns (16+17) 72 Analysis Patterns72 Analysis Patterns 38 CORBA Design Patterns38 CORBA Design Patterns ……..


Bright and Dark SidesBright and Dark Sides

Bright sideBright side Reuse of proven good designsReuse of proven good designs Can be applied in constructing new softwareCan be applied in constructing new software

Dark sideDark side Fail to properly evaluate a patternFail to properly evaluate a pattern Difficult to be applied to existing systemsDifficult to be applied to existing systems


The Truth aboutThe Truth aboutSoftware TechnologySoftware Technology

84% 84% of software projects are unsuccessful.of software projects are unsuccessful.

VendorsVendorsOur new technology Our new technology changes the whole changes the whole paradigm. paradigm. We’ll have all the features We’ll have all the features you need in six months.you need in six months.We make no warranty We make no warranty express. If it does something express. If it does something bad, it’s not their fault.bad, it’s not their fault.Proprietary technologies Proprietary technologies change every 4 to 18 change every 4 to 18 months.months.

Software gurusSoftware gurusNew method improves New method improves anything they said in the anything they said in the past.past.You need more tools!You need more tools!You need more training!You need more training!You need more consultancy!You need more consultancy!


Many Paths to DisasterMany Paths to DisasterStructured Programming

Artificial IntelligenceNetworking Technologies

Open SystemsParallel Processing


AntiPatternsAntiPatterns

NegativeNegative solutions that present more problems solutions that present more problems than they addressthan they addressNatural extension to design patternsNatural extension to design patternsBridge the gap between architectural concepts Bridge the gap between architectural concepts and real-world implementationsand real-world implementationsProvide the knowledge to prevent or recover Provide the knowledge to prevent or recover from themfrom them


AntiPattern ResearchAntiPattern Research

“ “The presence of ‘good’ patterns in a successful system The presence of ‘good’ patterns in a successful system is not enough; you also must show that those patterns is not enough; you also must show that those patterns are absent in unsuccessful systems. Likewise, it is useful are absent in unsuccessful systems. Likewise, it is useful to show the presence of certain patterns(AntiPatterns) in to show the presence of certain patterns(AntiPatterns) in unsuccessful systems, and their absence in successful unsuccessful systems, and their absence in successful systems.systems.

- James O. Coplien- James O. Coplien



Principal viewpointsPrincipal viewpoints DevelopmentDevelopment AntiPatterns AntiPatterns

Technical problems and solutions encountered by Technical problems and solutions encountered by programmersprogrammers

ArchitecturalArchitectural AntiPatterns AntiPatternsIdentify and resolve common problems in how Identify and resolve common problems in how systems are structured.systems are structured.

ManagerialManagerial AntiPatterns AntiPatternsAddress common problems in software processes Address common problems in software processes and development organizations.and development organizations.




Design Pattern and AntiPatternDesign Pattern and AntiPattern


Software RefactoringSoftware Refactoring

A form of code modification, used to A form of code modification, used to improve the software structure in support improve the software structure in support of subsequent extension and long-term of subsequent extension and long-term maintenance.maintenance.AntiPatternsAntiPatterns Define a migration (or refactoring) from Define a migration (or refactoring) from

negative solutions to positive solutions.negative solutions to positive solutions. Not only do they point out trouble, but they Not only do they point out trouble, but they

also tell you how to get out it.also tell you how to get out it.


The BlobThe Blob

General FormGeneral Form One class monopolizes the processing and One class monopolizes the processing and

other classes primarily encapsulate data.other classes primarily encapsulate data.

Key ProblemKey Problem The majority of the responsibility are allocated The majority of the responsibility are allocated

to a single class.to a single class. Procedural-style rather than object-oriented Procedural-style rather than object-oriented

architecturesarchitectures








SummarySummary

Structured v.s. Object Oriented ParadigmsStructured v.s. Object Oriented ParadigmsPatterns help Patterns help reuse design experiencesreuse design experiences

Especially in constructing new softwareEspecially in constructing new software understand the full capabilities of object-understand the full capabilities of object-

oriented designoriented design communication communication


SummarySummary

AntiPatternsAntiPatterns not against using patterns.not against using patterns. a more compelling form of patterns.a more compelling form of patterns.Each AnitPattern includes a solution + Each AnitPattern includes a solution + solution pair.solution pair. AntiPattern Solution Generates mostly AntiPattern Solution Generates mostly

negative consequences.negative consequences. Refactored Solution Generates mostly Refactored Solution Generates mostly

positive benefits.positive benefits.


SummarySummary

A B

RulesRules What to doWhat to do What not to doWhat not to do


ReferencesReferencesPatternsPatterns

GoF:GoF:E. Gamma, E. Helm, R. Johnson and J. Vlissides, E. Gamma, E. Helm, R. Johnson and J. Vlissides, Design Design Patterns - Elements of Reusable Object-Oriented SoftwarePatterns - Elements of Reusable Object-Oriented Software, , Addison-Wesley Publishing Company Inc., 1995.Addison-Wesley Publishing Company Inc., 1995.

POSA (Vol. 1):POSA (Vol. 1):F. Buschmann, R. Meunier, H. Rohnert, P. Sommerlad and M. F. Buschmann, R. Meunier, H. Rohnert, P. Sommerlad and M. Stal, Stal, Pattern-Oriented Software Architecture – A System of Pattern-Oriented Software Architecture – A System of PatternsPatterns, John Wiley & Sons Inc., New York, 1996., John Wiley & Sons Inc., New York, 1996.

POSA (Vol. 2):POSA (Vol. 2):D. Schmidt, M. Stal, H. Rohnert and F. Buschmann, D. Schmidt, M. Stal, H. Rohnert and F. Buschmann, Pattern-Pattern-Oriented Software Architecture – Patterns for Concurrent and Oriented Software Architecture – Patterns for Concurrent and Networked ObjectsNetworked Objects, John Wiley & Sons Inc., New York, 2000., John Wiley & Sons Inc., New York, 2000.


ReferencesReferences

AntiPatternsAntiPatterns W. J. Brown, R. C. Malveau, H. W. McCormick III, T. J. W. J. Brown, R. C. Malveau, H. W. McCormick III, T. J.

Mowbray, Mowbray, AntiPatterns - Refactoring Software, Architectures, AntiPatterns - Refactoring Software, Architectures, and Projects in Crisisand Projects in Crisis, John Wiley & Sons Inc., New York, 1998. , John Wiley & Sons Inc., New York, 1998.

Web SitesWeb Sites http://hillside.net/patterns/http://hillside.net/patterns/ http://www.antipatterns.com/http://www.antipatterns.com/


Q & AQ & A

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Patterns and AntiPatterns