Design Patterns Explained

CHAPTER 3
A Problem That Cries Out for
Flexible Code
Overview
This chapter gives an overview of a problem we want to solve:
extracting information from a large CAD/CAM database to feed a
complex and expensive analysis program. Because the CAD/CAM
system continues to evolve, the problem cries out for flexible code.
In this chapter, I give an overview of the CAD/CAM problem, the
vocabulary of the domain, and important features of the problem.
Extracting Information from
a CAD/CAM System
I am now going to review a past design of mine that got me on the
road to the insights contained in this book.
I was supporting a design center in which engineers used a CAD/
CAM system to make drawings of sheet metal parts. An example of
one of these parts is shown in Figure 3-1.
My problem was to write a computer tool to extract information
from the CAD/CAM system so that an expert system could use it in a
particular way. The expert system needed this information in order
to conrol the manufacturing of the part. Since the expert system was
complex to modify and would have a longer life than the current
version of the CAD/CAM system, I wanted to write the
information-extracting tool so that it could easily be adapted to new
revisions of the CAD/CAM system.
In this chapter
The problem: extract
information for an
expert system
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