Software Design

Architecture Design

Cohesion

  • Degree of interaction within a module

  • Coincidental Cohesion

    • A module has coincidental cohesion when if it performs multiple, completely unrelated actions
    • Problem
      • Degrades maintainability
      • Modules are not reusable
    • Solution
      • Break into separate modules

  • Logical Cohesion

    • A module has logical cohesion when it performs a series of related actions, one of which is selected by the calling module
    • Problem
      • The interface is difficult to understand
      • Code foe more than one action may be interwined
      • Difficult to reuse
    • Solution

  • Temporal Cohension

    • A module has temporal cohesion when it performs a series of actions related in time
    • Problem
      • Actions of the module are weakly related to one another, but strongly related to actions in other modules
      • Not reusable
    • Solution
      *

  • Procedural Cohesion

    • A module has procedural cohesion if it performs a series of actions related by the procedure to be followed by the product
    • Probelm
      • Actions are still weakly connected
      • Not reusable
    • Solution
      *

  • Communicational Cohesion

    • A module has communicational cohesion if it performs a series of actions related by the procedure to be followed by the product, but in addition all the actions operate on the same data
      • update record in database and write it to audit trail
      • calculate new coordinated and send them to terminal
    • Problem
      • Not flexible if intending to focus on some of the activities
      • lack of reusability
    • Solution
      *

  • Functional Cohesion

    • Module with functional cohesion performs exactly one action
    • get temperature of furnace
    • 2
    • 3
    • All of the element contribute to the performance of a single specific task
    • Advantage
      • More reusable
      • Corrective maintenance easier
      • Easier to extend product

  • Informational Cohesion

    • A module has informational cohesion if it performs a number of actions, each with its own entry point, with independent code foe each action, all performed on the same data structure
    • Advantage

Coupling

  • Content Coupling
    • Problem
      • Almost any change to one module require change to another
  • Common Coupling
    • Two modules are common coupled if they have write access to global data
    • Problem
      • Modules can have side-effects
      • Affects readability
      • entire module must be read to find out its function
      • difficult to reuse
      • expose to more data than necessary
  • Control Coupling
    • Two mudules are control coupled if one passes an element of control to the other
    • Operation code passed to the module
    • Control-switch passed as argument
    • Can be both good and bad depends on the parameters
    • Problem
      • not independent: Module b must know internal structure and logic of module a
      • Affects reusability
  • Stamp Coupling
    • Two modules are stamp coupled if a data structure is passed as a parameter, but the called module operated on some but not all of the individual components of the data structure
    • Problem
      • Not clear, without reading the entire module, which fields of a record are accessed or changed
        • Difficult to understand
        • Unlikely yo be reusable
        • Uncontrolled data access can lead to computer crime
    • Solution
      • Use simple data structures
      • Define class depend on interface
  • Data Coupling
    • Two modules are data coupled if all parameters are homogeneous data items
    • display time of arrival(flight number)
    • Compute product(first, second)
    • Get job with highest priority(job que)

Tools

  • Hierarchy chart
  • Hierarchy plus Input-Process-Output = HIPO

Detailed Design

  • Flowchart
  • Problem Analysis Diagram
  • N-S Digram