Structure Diagrams and Problem Representation

This lesson covers structure diagrams as a method for representing decomposed problems, as required by OCR J277 Section 2.1. Structure diagrams provide a clear, visual way to show how a complex problem is broken down into smaller sub-problems.

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What Is a Structure Diagram?

A structure diagram (also called a hierarchy chart or top-down design diagram) is a visual representation of how a problem has been decomposed into sub-problems. It uses a tree-like structure where:

• The top level shows the overall problem
• Each lower level shows the sub-problems at increasing levels of detail
• Lines connect each problem to its sub-problems

Structure diagrams are a direct visual representation of the decomposition process.

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How to Read a Structure Diagram

A structure diagram is read from top to bottom and (generally) from left to right:

                    Quiz Game
                        |
        ┌───────────────┼───────────────┐
        |               |               |
    Setup           Game Play       End Game
        |               |               |
    ┌───┴───┐      ┌────┼────┐      ┌───┴───┐
    |       |      |    |    |      |       |
  Load    Show   Show  Get  Check  Show   Ask
Questions Menu  Question Input Answer Score  Play
                                          Again

Level	Content
Level 0	The overall problem: Quiz Game
Level 1	Main sub-problems: Setup, Game Play, End Game
Level 2	Detailed sub-problems: Load Questions, Show Menu, etc.

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Creating a Structure Diagram

Step-by-Step Process

1. Identify the main problem — Write this at the top of the diagram.
2. Decompose into main sub-problems — These become the Level 1 boxes.
3. Decompose each sub-problem further — These become Level 2 boxes.
4. Continue until sub-problems are simple enough to be solved directly.
5. Draw connecting lines from each problem to its sub-problems.

Rules for Structure Diagrams

Rule	Explanation
One box at the top	The overall problem is a single box at Level 0
Each box connects to its parent	Lines show which sub-problems belong to which parent
Read top to bottom	Each level represents increasing detail
Each box is a sub-problem	Boxes represent tasks, not data
Sufficient detail	Decompose until each box represents a single, manageable task

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Worked Example 1: Library Management System

                    Library Management System
                              |
        ┌─────────────┬──────┴──────┬─────────────┐
        |             |             |             |
    Manage Books  Manage Loans  Manage Members  Reports
        |             |             |             |
    ┌───┼───┐    ┌────┼────┐   ┌───┼───┐    ┌───┼───┐
    |   |   |    |    |    |   |   |   |    |   |   |
   Add Edit Search Borrow Return Register Edit  Overdue Popular Member
   Book Book Book  Book   Book  Member Member Books  Books  History

Explanation:

Level	Sub-Problems
Level 0	Library Management System
Level 1	Manage Books, Manage Loans, Manage Members, Reports
Level 2	Add Book, Edit Book, Search Book, Borrow Book, Return Book, etc.

Each Level 2 sub-problem is simple enough to be solved directly with an algorithm.

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Worked Example 2: Login System