Collaborative design projects place additional burdens on current design documentation practices. The literature on group design has repeatedly documented the existence of problems in design decision making due to the unavailability of design information. This paper describes a data representation developed for collaborative mechanical design information. The data representation is used to record the history of the design as a sequence of design decisions. The resulting knowledge base records the final specifications, the alternatives which were considered during the design process, and the designers’ rationale for choosing the final design parameters. It is currently used in a computerized knowledge base system under development by the Design Process Research Group (DPRG), at the authors’ institution (OSU).