9. Goals of structural analysis
• Early fixing design violations
• Keeping code complexity on a manageable level
under constant change rain
• Getting the «big picture»
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12. Release Reuse Equivalency
«The unit of reuse is the unit of release»
Criterion for grouping artifacts is convenience for
reuse and release
Component
lv.jug.api
lv.jug.logic
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13. Common Closure Principle
«Classes that change together belong together»
If classes that change together are in the same
Package, then the impact on other packages is
minimized. Group classes open to certain changes.
lv.jug.domain.client
lv.jug.dao.client lv.jug.domain.client
lv.jug.service.client
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14. Common Reuse Principle
«Classes in a package are reused together»
A dependency upon a package is a dependency
upon everything within the package.
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16. Acyclic Dependencies Principle
«The dependencies between packages must not
form cycles»
Can be solved by:
• Splitting packages (CRP)
• Reorganizing packages
• DIP & Interface Segregation
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17. Abstractness of a package
A(P) = AC(P) / TC(P)
A(P) ∈ [ 0..1 ]
…where
P = package
AC = abstract type count
TC = total type count
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18. Instability of a package
I(P) = EC(P) / ( AC(P) + EC(P) )
A(P) ∈ [ 0..1 ]
…where
P = package
EC (Efferent Coupling) = number of outgoing dependencies
AC (Afferent Coupling) = number of incoming dependencies
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19. Stable Abstractions Principle
«A package should be as abstract as it is stable»
Distance (D)
Zone of uselessness
D=A+I-1
Zone of pain
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Rigidity(tverdostjmonolitnostj) – monolith, difficult to change, cascade to dependent modulesFragility – breaking in many places with no conceptual relationshipImmobility – inability to reuse components, decompose system, big transitive dependency tailViscosity (vjazkostj) –when “normal” change is harder to employ than a hack due to design (unclear dependency) or environment (compilation 1H)Opacity – can’t understand the purpose of the class/package
Avoiddevelopment interference, forexampleServe as a foundationforfuturemodularization
Imagine that every change increments version and makes class unsuitable for clients of the previous version
Reason:Minimizeimpact on the client with different releasecycleЕсли я положу в библиотеку или пакетто, что сложно реюзать или то что нежелательно реюзать, это непосредственно влияет на клиента и мою необходимость релизить повторноОдиночные классы часто не реюзаются. Необходимо создавать набор крассов (потенциально формирующий связный компонент)Either all of the classes in a package are reusable or non of them are.
Reason:the more packages change in any given release, the greater work to rebuild, test and deploy the releasemimimize the number of packages that are changed in any givenreleaseIf the code in an application must change, where would you like those changes tooccur: all in one package, or distributed through many packages?ModularContinuity – whensmallrequirementchangeyieldssmallchangeintheresult
Reason:Ifclass changes, its package changes (and classesinside).If a package is being releasedbecause of changes to a class that I don’t care about, then I will not be very happy abouthaving to revalidate my application.Every time the used package (P2) is released, the using package (P1) must be revalidated
Cycled = only can be used & understood togetherNo dependency cycles within the design layerGraph is acyclic if and only if it has no tanglesBreak minimum feedback arc
1 класс и не абстрактный = 01 класс и абстрактный = 12 класса пополам = 0,5
Responsible class – a lot of incoming dependenciesDependent class – a lot of outgoing dependencies0,5для пакетов с одинаковым количеством входящих и выходящих связей
Stable = hard to change, Unstable – easy to change, butfragile. We don’t want all packages to be stableBy sticking to this principle we avoid getting packages which are used heavily by the rest of the application and which, at the same time, have a low degree of abstraction
Stable = hard to change, Unstable – easy to change, butfragile. We don’t want all packages to be stableBy sticking to this principle we avoid getting packages which are used heavily by the rest of the application and which, at the same time, have a low degree of abstraction
Stan4j: Acyclic dependencies forming Tangles
Enforcing rules with MackerScreenshot of rotting structure (DC)Screenshot of clean structure (Deposits)
