This book contains everything you need to know to understand the theory of computerized trading systems. It goes through the process of choosing a strategy, implementing it in algorithm form, perfecting variables, and optimization. The most important parts, in my opinion, are those regarding tests of statistical significance of the test results. The author is also careful to caution against any "over-optimization," which is the bane of any trading system.
Incedentally, I manage the technical analysis arm of a newsletter that attempts to forecast the best performing Fidelity Select mutual fund. This book was an asset during the implementation of my trading system. I would choose it before "The Mathematics of Technical Analysis," by Clifford Sherry, for example.
The trading system paradigm detailed in this book is based on technical analysis; the use of mathematical tools to estimate the future performance of a security. Technical analysis is, of course, at odds with the strict versions of the efficient market theory. Do you believe that stock performance is deterministic, that future price changes can be inferred from past ones? If so, this is the book to use to implement your computerized trading system.