The program development life cycle and decomposition

Last time

Before we start: last time, in Artificial intelligence, expert systems and machine learning, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Nobody builds a house without a plan

Nobody builds a house by laying bricks and hoping. They investigate what is needed, then plan it, then build it, then check it. Programmers work in the same order. Cambridge calls it the program development life cycle, and you need four stages.

The four stages

The stages are analysis, design, coding and testing. If testing finds problems, the programmer goes back to an earlier stage. Maintenance is not one of the four stages you need. Writing maintenance or evaluation as a stage scores no marks.

What happens in each stage

In analysis, the problem is defined and the requirements are identified, using abstraction and decomposition. In design, the solution is planned, using structure diagrams, flowcharts and pseudocode. In coding, the program is written, with iterative testing. In testing, the finished program is run with test data.

Analysis

In analysis, the problem is investigated and clearly defined. The requirements are identified: what the program must do. Unnecessary detail is removed, and the problem is broken into parts.

Abstraction

Abstraction means removing unnecessary detail, and keeping only what is needed. A map of a train network shows stations and lines, but not buildings or roads. A paint calculator needs the wall size and the price, but not the brand of the paint.