Worksheet

A14.4 System design

Software development, law and ethics · A level · OCR H446 1.2.3, AQA 7517 4.13.1.2, Eduqas A500QS 1.6 · about 40 min

What this lesson is about

Structure charts, data flow diagrams, designing data, algorithms and the user interface, and printing a structure chart with recursion.

• What a design contains
• Top-down design and structure charts
• Data flow diagrams
• Designing the data
• Designing the interface
• Designing the algorithms

Questions 6 marks in all

1. [1 mark]In a structure chart, what does a small arrow with an open circle show?

   1. AA data couple: data passed between two modules
   2. BA loop
   3. CA decision
   4. DAn external entity

2. [1 mark]In a data flow diagram, which of these flows breaks the rules?

   1. AData flowing directly from one data store to another
   2. BData flowing from an external entity to a process
   3. CData flowing from a process to a data store
   4. DData flowing from a process to an external entity

3. [1 mark]Which of these should a design plan, according to AQA?

   Tick every answer that is true.

   1. AThe data structures for the data model
   2. BThe algorithms
   3. CThe modular structure
   4. DThe human user interface
   5. EThe exam board's mark scheme

4. [1 mark]The robot's screen shows errors only as red text. Which change best improves accessibility?

   1. AAdd a symbol and a clear message, so colour is not the only way the error is shown
   2. BMake the red text brighter
   3. CRemove the error messages
   4. DUse a smaller font to fit more on screen

5. [1 mark]What name is given to design that starts with the whole problem and repeatedly breaks it into smaller sub-problems?

6. [1 mark]A structure chart is stored as a dictionary. What does this print?

   chart = {"robot": ["sense", "act"], "act": ["drive", "beep"]}
   def show(module, depth):
       print("-" * depth + module)
       for sub in chart.get(module, []):
           show(sub, depth + 1)
   show("robot", 0)

The task: print the structure chart

chart is a dictionary describing a structure chart: each key is a module name (a string), and its value is the list of that module's sub-modules, in left-to-right order. A module that is not a key has no sub-modules. Write a recursive procedure show(module, depth) that prints the module's name after 2 * depth spaces, then calls itself for each of the module's sub-modules with depth + 1. Call it as show("delivery robot", 0). While it runs, count every module printed and collect the leaves (modules with no sub-modules) in the order they are printed. After the chart, print modules: <n> and then leaves: <names>, with the names separated by , . The robot stays still.

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

chart = {
    "delivery robot": ["plan route", "drive route", "report"],
    "plan route": ["read map", "shortest path"],
    "drive route": ["drive leg", "check gap"],
    "drive leg": ["set motors", "read heading"],
    "report": ["format message", "send message"],
}

Plan your program here, then type it in and press Run.

Do it on the robot
www.bugbotlab.com/learn/a14-4-system-design/
The simulator checks it and tells you when it passes. Nothing to install, no account.

Challenges

1. Draw a data flow diagram for a system where students book a robot for a lesson and a technician gets a daily list of bookings.
2. Change show so it also prints each module's depth in brackets, and prints depth of chart: <n> at the end.
3. The robot's screen shows errors in red text only. Give two changes that make it accessible, and say which users each helps.