Program Development Life Cycle - Design | Computer for GCSE/IGCSE - Year 11 PDF Download

Decomposition

• Decomposition entails dividing a complex problem into smaller, comprehensible sub-parts, making it more manageable. These sub-parts are further divided until they are easily solvable and cannot be broken down any further. For instance, preparing for school in the morning serves as an example of decomposition.
  • Step 1: Wake up
  • Step 2: Get breakfast
  • Step 3: Brush teeth
  • Step 4: Put clothes on
  • Step 5: Ensure the bag and school supplies are ready
  • Step 6: Find transportation to school (walk, bus, car, bike, etc.)
• These steps can be further detailed. For example, "Step 2: Get breakfast" would involve:
  • Step 2.1: Get a bowl
  • Step 2.2: Get cereal
  • Step 2.3: Get milk
  • Step 2.4: Get a spoon
  • Step 2.5: Put cereal in a bowl
  • And so on...
• After creating the requirements document, developers must design the architecture and algorithms to address the problem:
  • Structure charts illustrate the hierarchical breakdown of tasks.
  • Flowcharts visually depict the sequence of tasks.
  • Pseudocode, often derived from flowcharts, aids programmers in translating task instructions into code seamlessly.
• Solution design outlines the tasks required, their methods, and their interconnections.
• Computer systems encompass various components such as software, hardware, data, networking, and human users.
• Systems can be broken down into sub-systems, which can then be further decomposed into smaller units, each with a specific purpose. This process of breaking down systems is referred to as top-down design.

Decomposing a System

• Stepwise refinement involves breaking down a problem into subsystems to facilitate easier problem-solving and system creation.
• This decomposition yields smaller, more manageable, and comprehensible sub-parts.
• Developers can then assign each subsystem to a developer or group for the creation of subroutines. Simultaneous development of subsystems reduces project timelines, particularly for large projects.
• Decomposing the system via stepwise refinement entails consideration of four critical areas:
  • Inputs: Data inputted into the system.
  • Processes: Subroutines and algorithms transforming inputs and stored data into outputs.
  • Outputs: Data produced by the system, such as on-screen or printed information.
  • Storage: Data stored on physical devices like hard drives.
• Thorough understanding of all aspects by developers is essential to problem-solving.
• Various methods are employed for designing and constructing solutions.

Structure Diagrams

• Structure diagrams illustrate hierarchical top-down design visually.
• Each problem is segmented into sub-problems, and each sub-problem is further divided into more detailed tasks.
• At each level, the problem is broken down into tasks that can be accomplished using a single subroutine.

Flowcharts

• Flowcharts provide a visual representation of algorithms through diagrams.
• Each flowchart starts with a beginning and ends with an end, with arrows indicating the sequence of tasks or instructions.
• Flowcharts consist of different symbols:
  • Terminator Symbols: Also referred to as Begin/End symbols, these markers signify the initiation and conclusion of a flowchart.
  • Process Symbols: These symbols depict basic actions like assigning values or carrying out arithmetic operations on those values.
    • Processes can also stand for other flowcharts or summarized actions. For instance, activities like searching or sorting a list are intricate processes that may necessitate their individual flowcharts. A process symbol could be employed to illustrate sorting or searching in a distinct flowchart, denoted by a process symbol with an additional bar on each side.
  • Input/Output Symbols: These symbols showcase the intake and output of data.
  • Decision Symbols: Utilized to determine whether to follow one of two paths by responding to a true/false or yes/no query. They are beneficial for selection and iteration purposes.
  • Flow Lines: Flow lines incorporate arrows to indicate the flow's direction and the subsequent task to execute. Typically, these arrows move from top to bottom and left to right.

Pseudocode

• Pseudocode is like a simplified programming language without strict syntax. It's a way to plan out programs using plain English instead of actual code.
• In pseudocode, developers use English words and phrases to outline the steps of a program. While it resembles real code, it cannot be executed on a computer.
• The main goal of pseudocode is to help programmers understand how to build a program, regardless of the programming language they will ultimately use.
• Even though pseudocode doesn't have a fixed syntax, it's crucial to maintain a consistent style. This consistency aids in readability and speed when translating pseudocode into actual programs.
  • Examples of a Consistent Style:
    • Keywords are written in capital letters, for instance, INPUT, OUTPUT, IF, THEN, ELSE
    • Variable and subroutine names should start with capital letters like Age, Name, Date, CalculateArea, Sortlist
    • Indentation is useful for iteration and selection in programming