1. 1. Systems and Software Development
1.1 The Systems Life Cycle

2. 1.1.6 Design: Approaches

3. Top-down or bottom-up?
Modular decomposition is a top-down approach: consider the whole problem and break it into parts.
Bottom-up approaches are not common: take many small modules and build them into a larger product (see what evolves...).

4. Advantages of modularity
Debugging the program is easier – errors can usually be isolated to a particular module.
Time saving – each module is worked on by a team, who can move to another module if they finish early or that team is struggling.

5. Advantages of modularity
Easier to understand – managers can get an overview without having to know the details.
More flexible – modules may be dropped if not working or old ones picked “off the shelf”.
Specialisation – programmers become experts on certain modules.

6. How modular?
Eventually modules could equate to classes or even methods.
Eventually designers write pseudocode (informal provisional code) for each module.

7. Prototyping
A prototype is a simplified version of a proposed solution for presentation to the end- user during the analysis or design phase.
Not fully functional but allows for user feedback.
Not necessarily using the same software e.g. could be a presentation.

8. Advantages of prototyping
Helps end-user be more specific about what they actually need.
Different versions of the prototype allow the designer and end-user to express a preference.
Allows problems to be caught and changed earlier (i.e. cheaper and safer).

9. Solution efficiency
Designs are chosen and prototypes tested not just for whether they work but also for efficiency:
speed,
reliability,
memory use,
processor use.

10. Efficiency: memory
If records have fixed-length fields, it is possible to calculate how much space the data file needs.
In Java,
bytes use 1 byte (!),
chars use 2,
ints use 4,
doubles use 8.

11. Efficiency: memory
If the whole file is loaded into IAS, how much memory will be required?
Can the whole project be stored on a memory stick?
How long would it take to download?
What are the ideal length for String variables (too short - truncates values, too long - overflows memory)?

12. Efficiency: processor
Is this less important with today’s processors?
Sorting is very processor-intensive.
Look for efficient algorithm designs e.g.
quicksort (HL) over bubble sort,
if using bubble sort, use a flag to indicate no more passes are needed when the data are sorted.