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Stepwise refinement

What is stepwise refinement?

  • Stepwise refinement is the process of breaking down a complex problem into smaller, more manageable sub-problems in a logical order

  • Each sub-problem is refined step by step until it is simple enough to be solved with a single subroutine or module

  • This method ensures that the overall problem can be solved by addressing each part individually, in a structured and efficient way

Relationship to decomposition and top-down design

  • Decomposition is the general concept of breaking a problem down into smaller parts

  • Top-down design is the strategy used to perform decomposition

  • Stepwise refinement is the process used in top-down design to gradually refine each major task into simpler sub-tasks

  • In other words, stepwise refinement is how top-down design is implemented

Benefits of stepwise refinement

  • Helps developers understand and organise the structure of a program

  • Makes testing and debugging easier through unit testing of individual subroutines

  • Encourages code reuse by breaking tasks into reusable components

  • Supports collaborative development, as tasks can be divided between team members

  • Each subroutine should:

    • Be clear and focused on a single task

    • Be simple enough to implement directly

    • Not need further breakdown

Example: Calculating student grades

  • Here’s how stepwise refinement could be applied to a program designed to calculate student grades for a teacher’s classes:

Top-level task:

  • Calculate grades for all students in all classes

Stepwise refinement:

  • Step 1 – Calculate the grade for each assessment

    • For each question:

      • Mark the question

      • Store the mark

    • Sum the marks for all questions in the assessment

  • Step 2 – Calculate the average grade for each student

    • Add together grades from all assessments

    • Divide by the number of assessments

    • Store the average

  • Step 3 – Repeat for each class

    • For every student in the class:

      • Perform Steps 1 and 2

  • This structured breakdown allows each task to be turned into a subroutine, simplifying the design, implementation, and testing of the overall program

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