This paper describes a software tool called DRed (the Design Rationale editor), that allows engineering designers to record their design rationale (DR) at the time of its generation and deliberation. DRed is one of many proposed derivatives of the venerable IBIS concept, but by contrast with other tools of this type, practicing designers appear surprisingly willing to use it. DRed allows the issues addressed, options considered, and associated arguments for and against, to be captured graphically. The software, despite still being essentially a research prototype, is already in use on high profile design projects in an international aerospace company, including the presentation of results of design work to external customers. The paper compares DRed with other IBIS-derived software tools, to explain how it addresses problems that seem to have made them unsuitable for routine use by designers. In addition to the capture and presentation of the DR itself, the set of linked DR graphs can be used to provide a map of the contents of an electronic Design Folder, containing all the documents created by an individual or team during a design project. The structure of the knowledge model instantiated in such a Design Folder is described. By reprising a design case study published at the DTM 2003 conference, concerning the design of a Mobile Arm Support (MAS), the DRed knowledge model is compared with the previously proposed Design Data Model (DDM), to show how it addresses the shortcomings identified in the DDM. Finally the methodology and results of the preliminary evaluation of the use of DRed by aerospace designers are presented.
