  This paper presents a taxonomy for analytical spreadsheet models. It
considers both the use case that a spreadsheet is meant to serve, and the
engineering resources devoted to its development. We extend a previous
three-type taxonomy, to identify nine types of spreadsheet models, that
encompass the many analytical spreadsheet models seen in the literature. We
connect disparate research literature to distinguish between an "analytical
solution" and an "industrial-quality analytical spreadsheet model". We explore
the nature of each of the nine types, propose definitions for some, relate them
to the literature, and hypothesize on how they might arise. The taxonomy aids
in identifying where various spreadsheet development guidelines are most
useful, provides a lens for viewing spreadsheet errors and risk, and offers a
structure for understanding how spreadsheets change over time. This taxonomy
opens the door to many interesting research questions, including refinements to
itself.
