Program design

The design document you submit should consist of

A title, author, date and other preliminaries. (As usual with assessed work, please use your Registration number, not your name.)
An introduction, which explains what the program is for, and gives a high-level account of how it works.
A structure, typically describing briefly the set of classes you intend to write. You should explain the idea behind each class without going into much detail at this stage. You should also explain why it makes sense to have each of the classes you describe.
A section giving more detail on each class. Here, you will describe the important variables and methods. You don't need to describe every method, just the important ones. You might give pseudocode to describe the algorithms you intend to implement. Include enough information so that the reader can clearly see how information flows in your program. Your description should make clear what are the important arguments for each method, and what it returns.

Your set of classes should be loosely coupled, but each class should show high cohesion. Coupling is a measure of the interdependence between classes. If every object has a reference to every other object, then there is high coupling, and this is undesirable because there's potentially too much information flow between objects. Low coupling is desirable: it means that objects work more independently of each other. Low coupling minimizes the "ripple effect" where changes in one class cause necessity for changes in other classes. Cohesion is a measure of strength of the association of variables and methods within a class. High cohesion is desirable because it means the class does one job well. Low cohesion is bad because it indicates that there are elements in the class which have little to do with each other. Modules whose elements are strongly and genuinely related to each other are desired. Each method should also be highly cohesive. Most methods have only one function to perform. Don't add 'extra' instructions into methods that cause it to perform more than one function.

Important points about submission:

Please submit your design electronically, using the procedure described on the main web age.
Your design should be in PDF or HTML. These are open standards. MS-Word is not an open standard and should be avoided for distributing documents.
The marking scheme will focus on quality, not quantity. Please make every sentence meaningful. Make every word count. Style hints. Use diagrams if they will help your explanation.

Mark Ryan, 16 October 2004.