Monday, August 08, 2005

Problem Frames

Context: Software Requirements & Specifications, Software Design, Problem Analysis

When you analyse a problem you see what kind of problem it is, and identify the concerns and difficulties you will have to deal with to solve it. Problem analysis takes you from the level of identifying the problem to the level of making the descriptions needed to solve it. But most realistic problems are too big and complex to handle in just two levels like this. Another level is needed: structuring the problem as a collection of interacting subproblems.If your structuring is successful, the subproblems will be smaller and simpler than the problem you started with, and their interactions will be clear and understandable. Then you can analyse each subproblem separately, as a simple problem on its own, and make the descriptions it needs.

Problem frames help in problem analysis and structure.
- help you by defining different simple problem classes. When you analyse the subproblem, you see what concerns it raises according to the problem frame that fits it. The frame shows you what you must do to solve it.
- problem frames help you to focus on the problem, instead of drifting into inventing solutions. They do this by emphasising the world outside the computer, the effects that are required there, and the relationships among things and events of the world

Problem frames share much of the spirit of design patterns. Design patterns look inwards towards the computer and its software, while problem frames look outwards to the world where the problem is found. But they both identify and describe recurring situations. They provide a taxonomy within which each increment of experience and knowledge you acquire can be assigned to its proper place in a larger scheme, and can be shared and accessed more effectively. So just as in object-oriented design a familiarity with design patterns allows you to say 'we need an instance of the decorator pattern here', so in problem decomposition a familiarity with problem frames allows you to say 'this part of the problem is a workpieces problem'. Having identified a part of a problem with a recognised problem frame, you can draw on experience associated with the frame.



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