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principles:low_coupling [2012-12-17 22:45] – added link christianprinciples:low_coupling [2021-09-02 12:46] – old revision restored (2021-03-29 09:33) 65.21.179.175
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-===== Definition =====+===== Principle Statement =====
  
 [[glossary:Coupling]] between [[glossary:modules]] should be low. [[glossary:Coupling]] between [[glossary:modules]] should be low.
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 But if coupling is low, there are only few assumptions between the modules which can be violated. This reduces the chance of [[glossary:ripple effects]]. But if coupling is low, there are only few assumptions between the modules which can be violated. This reduces the chance of [[glossary:ripple effects]].
 +
 +
 +===== Strategies =====
 +
 +  * Indirection: 
 +  * Dependency Inversion/Abstract Couplings:
 +  * Use lower form of coupling:
 +  * Merge modules:
 +  * Hide information
 +
 +===== Caveats =====
 +
 +Coupling can be reduced by several technical measures (see [[#strategies]]). But while these measures reduce the coupling technically, they do not necessarily reduce the logical coupling. In such a case two modules A and B may seem decoupled, but ripple effects may occur anyway because of the logical coupling. In such a case it is better to make the coupling explicit by not applying a decoupling strategy. It may also be possible to find a better suitable strategy or a better way of applying the strategy to also get rid of the logical coupling.
 +
 +Furthermore note that coupling to a stable module is often no problem. The problematic cases are couplings to unstable modules. This means that applying decoupling strategies is beneficial when a coupling to an unstable module is reduced. But it may not be beneficial in the other cases.
 +
 +See also section [[#contrary principles]].
  
  
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 ===== Evidence ===== ===== Evidence =====
 /* Comment out what is not applicable and explain the rest: */ /* Comment out what is not applicable and explain the rest: */
-/*[[wiki:Proposed]]*/+/*  * [[wiki:Proposed]]*/ 
   * [[wiki:Examined]]   * [[wiki:Examined]]
-  * [[wiki:Accepted]]+  * [[wiki:Accepted]]: The concept of low coupling is widely known and described in several well-known books for example in Craig Larman's //Applying UML and Patterns//
  
-/*[[wiki:Questioned]]*/+/*  * [[wiki:Questioned]]*/
  
  
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 ==== Specializations ==== ==== Specializations ====
  
-  * [[principles:Information Expert]] +  * [[Constantine's Law]]: Constantine's Law is just the combination of the two principles LC and HC. 
-  * [[principles:Constantine's Law]]+  * [[Dependency Inversion Principle]] (DIP): LC aims at reducing the dependencies to other modules. One way to do so is to only depend on abstractions. DIP is about this aspect.
  
 ==== Contrary Principles ==== ==== Contrary Principles ====
  
-  * [[principles:Keep It Simple Stupid]]: Reducing the coupling often involves the use of complicated interaction patterns, indirections, etc. +  * [[Keep It Simple Stupid]] (KISS): Reducing the coupling often involves the use of complicated interaction patterns, indirections, etc. 
 +  * [[High Cohesion]] (HC): A system consisting of one single module has a very low coupling as there are no dependencies on other modules. But such a system also has low cohesion. The other extreme, very many highly cohesive modules, naturally has a higher coupling between the modules. So here a compromise has to be found. 
 +  * [[Rule of Explicitness]] (RoE): Direct communication typically has the disadvantage of a higher coupling. Indirection reduces coupling but creates implicit/indirect communication paths.
 ==== Complementary Principles ==== ==== Complementary Principles ====
  
-  * [[principles:High Cohesion]] +  * [[Tell, don't Ask/Information Expert]] (TdA/IE): IE may help to reduce coupling. Although there are also contrary cases (see [[Tell, don't Ask/Information Expert#caveats]]). 
-  * [[principles:Model Principle]]+  * [[Model Principle]] (MP): LC aims at reducing the dependencies to other modules. So a module shall depend on only a few others. MP now tells which dependencies are allowed and which aren't. 
 +  * [[Information Hiding/Encapsulation]] (IH/E): Higher forms of couplings (especially content couplings) break encapsulation.
  
 ==== Principle Collections ==== ==== Principle Collections ====
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 {{page>collections:OOD Principle Language#Box}} {{page>collections:OOD Principle Language#Box}}
 {{page>collections:GRASP#Box}} {{page>collections:GRASP#Box}}
 +{{page>collections:Principles in "The Pragmatic Programmer"#Box}}
  
-===== Example =====+===== Examples =====
  
  
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   * [[wiki>CouplingAndCohesion]]   * [[wiki>CouplingAndCohesion]]
   * Martin Fowler: //[[http://martinfowler.com/ieeeSoftware/coupling.pdf|Reducing Coupling]]//    * Martin Fowler: //[[http://martinfowler.com/ieeeSoftware/coupling.pdf|Reducing Coupling]]// 
 +  * Craig Larman: //Applying UML and Patterns – An Introduction to Object-Oriented Analysis and Design and Iterative Development//
 +
principles/low_coupling.txt · Last modified: 2021-10-18 21:49 by christian