Cohesion metrics & coupling metrics are metrics in Component-level design

Discussion

• Nirja Shah   -Posted on 23 Oct 15
  Component-level design
  - It occurs after the first iteration of the architectural design
  
  - It strives to create a design model from the analysis and architectural models
  
  - The translation can open the door to subtle errors that are difficult to find and correct later
  
  - “Effective programmers should not waste their time debugging – they should not introduce bugs to start with.” Edsgar Dijkstra
  
  - This design can be represented using some intermediate representation (e.g. graphical, tabular, or text-based) that can be translated into source code
  
  - To avoid the introduction of errors the design of data structures, interfaces, and algorithms should conform to well-established guidelines.
  
  Cohesion
  - Cohesion is the “single-mindedness’ of a component
  - It implies that a component or class encapsulates only attributes and operations that are closely related to one another and to the class or component itself
  - The objective is to keep cohesion as high as possible
  - The kinds of cohesion can be ranked in order from highest (best) to lowest (worst)
  - Functional
  A module performs one and only one computation and then returns a result
  - Layer
  A higher layer component accesses the services of a lower layer component
  - Communicational
  All operations that access the same data are defined within one class
  
  Coupling
  - As the amount of communication and collaboration increases between operations and classes, the complexity of the computer-based system also increases
  - As complexity rises, the difficulty of implementing, testing, and maintaining software also increases
  - Coupling is a qualitative measure of the degree to which operations and classes are connected to one another
  - The objective is to keep coupling as low as possible

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