Study the past, if you would divine the future. -CONFUCIUS A well written, organized, and concise survey is an important tool in any newly emerging field of study. This present text is the first of a new series that has been established to promote the publications of such survey books. A survey serves several needs. Virtually every new research area has its roots in several diverse areas and many of the initial fundamental results are dispersed across a wide range of journals, books, and conferences in many dif­ ferent sub fields. A good survey should bring together these results. But just a collection of articles is not enough. Since terminology and notation take many years to become standardized, it is often difficult to master the early papers. In addition, when a new research field has its foundations outside of computer science, all the papers may be difficult to read. Each field has its own view of el­ egance and its own method of presenting results. A good survey overcomes such difficulties by presenting results in a notation and terminology that is familiar to most computer scientists. A good survey can give a feel for the whole field. It helps identify trends, both successful and unsuccessful, and it should point new researchers in the right direction.