The Program Development Cycle

• We will look at a classical method of software design called the Waterfall Model.
• This model is pictures in your book on page 3.
• It consists of a number of interrelated steps in three phases.
  • Problem Solving Phase - attempt to understand the problem and specify what the software should do.
  • Implementation Phase - Turn the design from the previous phase into a working software system.
  • Maintenance Phase - Modify, repair and extend the existing product.
• The Problem Solving Phase
  • Analysis and Specification
    • You need to determine exactly what the problem you will be solving is.
    • Sometimes problems are well specified and you know what to do.
    • For example, any problem on page 86 or 87.
    • Sometimes this is less so
    • like this one
    • You need to read and understand the problem.
    • You need to determine what you have as input and what you are to produce as output.
    • You frequently need to ask for clarification, explanation or further information at this phase of the development process.
  • General Solution
    • Once you understand the problem how do you solve it?
    • An algorithm is a set of instructions which solve a problem in a finite amount of time.
    • Algorithms come in two flavors.
      • Very detailed solutions to well known problems (see the algorithms book)
      • A general plan, much like an outline, for solving a problem.
    • While I expect you will eventually become good at the first, I am very interested in you becoming good at the second.
    • The algorithm provides a blue-print, or a plan for constructing your program.
    • We will work on these throughout the semester.
    • I ask that you make an honest attempt to create algorithms BEFORE you implement your code.
  • Solution Verification
    • Once you have an algorithm, you should test this algorithm.
    • To do this, you need example input and the corresponding output.
    • You should step through your algorithm, checking to see if the input produces the output (your algorithm works)
    • As you create the algorithm, you will discover test data.
    • Is there any point in implementing an algorithm which does not work?
• Implementation Phase
  • Concrete Solution
    • Translate your algorithm to a program.
    • This involves knowing the programming language.
    • And understanding how this language works.
  • Test
    • Use the test data from the design phase to make sure your program works for this data.
    • As you implement the code, you will frequently discover other places/data that you should test.
    • This is an important, yet frequently ignored phase of software development.
• Maintenance Phase
  • Use the program.
  • Maintain
    • Fix bugs (then test again)
    • Add features (then test again)
• This is a loop, frequently you will return to a previous stage as you try to complete a later stage.