Software Modules in Software Design

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Software Modules in Software Design
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What is a Module?

• A set of one or more contiguous program
  statements having a name by which other parts of
  the system can invoke it, and preferably having
  its own distinct set of variable names.
  Stevens, Myers74

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• A module is a lexically contiguous sequence of
  program statements, bounded by boundary elements,
  having an aggregate identifier. Yourdon,
  Constantine 79

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Avantages

• Decomposition into easily dealt with pieces
• can abstract call by descriptive naming
• break up program into system architecture
• reduce complexity that one inspector needs to
  view when considering a design concept
• debug by following trail of destruction through
  interfaces to independent module for repair
• what properties does a module need to accomplish
  all this?

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Conservation of Complexity

• Move complexity of singular program module to
  interfaces between less complex modules
• hierarchy and decomposition, divide and conquer
• Net complexity is conserved, but it is divided so
  as to give programmers some leverage?

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Cohesion and Coupling(a system concept!)

• Cohesion
• the degree of interaction within a module
• Coupling
• the degree of interaction between modules

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Module Cohesion

1. Informational
2. Functional