toring of their effectiveness. Occupational structures serve a defining function that tends to be backward-looking, reflecting what existed in the past, rather than forward-looking, reflecting trends in the changing organization of work.

Choices of methodology and technology for occupational analysis are guided by theories of work and occupations, represented most clearly by existing occupational structures. The primary consideration in occupational analysis is to devise a system that provides a basis for understanding the world of work, one that is grounded in this reality. Any arbitrary structure will not suffice. The relevance of a system issues from its connection to reality (recognizing that the structure and the reality can never be fully separated), along with the extent to which it serves its intended purposes. To the extent that reality is changing or undergoing significant shifts, an occupational analysis system should be able to measure the change, and the categories should reflect it.

We begin our discussion with a brief history of occupational analysis systems; then we describe contributions of two different types of systems—descriptive and enumerative—and assess how well the most current system under development performs the two key functions of occupational analysis: tracking changes in work and supporting employment decisions and career counseling. In our analysis we examine the extent to which existing and prototype systems of occupational analysis systematically address the major themes of heterogeneity detailed throughout this volume: increasing heterogeneity of the workforce, increasingly fluid boundaries between who performs which jobs, and the increasing range of choices around how work is organized and structured.

The development and evolution of occupational analysis systems has been closely tied to wars and other major social changes. Most observers note that occupational analysis systems evolved principally in response to one or another practical personnel problem, and they have often involved a key role for government in their initiation and definition (see Primoff and Fine, 1988; Mitchell