Introduction

Abstract

Every profession has its tools of the trade, which are developed through the joint efforts of theoreticians and practitioners, and which generally evolve over many years of use and refinement. The tools which survive the natural selection process reflect the best ideas of theoreticians and inventors, the experiences of artisans and practitioners, and the contemporary technology of the field. Tools constantly undergo changes and refinements; but they provide, at any point in time, a collection of implements with which practitioners in the field may more effectively and efficiently perform their work.