Metaphors and cost significance in a conceptual design decision support system

"Currently in the research community, there are a number of styles of conceptual design software being developed. This paper describes the development of a Decision Support System (DSS) which belongs to that class of systems where the search is undertaken by the user with the software providing information and answers. Industrial evaluation by the authors and others has shown that such a style of interaction is well received by practising designers provided that the algorithms and processes used are sufficiently transparent for them to understand and have confidence in the way that the system reaches derives its answers. The system which forms the subject of this paper fully conforms to the above, with all algorithms, constraints and rules being easily accessible to the user. The system is known by the acronym COSTEST. COSTEST provides facilities for the designer to undertake the conceptual design of beam / slab bridges to a far higher level of accuracy than is possible with current practice. It includes facilities for sizing the super and sub-structures as well as FE analysis, a cost estimation routine, a database of structural sizes and material properties and the ability to produce a simple general arrangement and a client report. To enable the user to navigate through the system, understand what facilities are available and what their significance is, the user interface has been structured using the metaphor of the design office. The interface is arranged as a corridor off which are facilities such as a superstructure design office, an estimator’s office, etc. These are arranged around a direct manipulation representation of the sectional general arrangement. It is postulated that such an arrangement reduces the distance between the user’s way of thinking about the design problem and the system’s representation, thus making the system easier to use. Such Visual Interactive Modelling of the domain has been shown to allow users to use the software to learn about their own subjective values while dealing with the technical issues. The cost estimation component of COSTEST is based on the concept that for any bridge 80% of the total cost is contained in the 20% of items that are most cost significant. This idea has been developed by Horner but further analysis of existing bridges was undertaken as part of this work. The result is a simple cost model which is easy to use and yet far more accurate than current conceptual design practice. In particular it allows an accurate comparison to be made between options. COSTEST has been developed in conjunction with a number of practising bridge designers and the final system has been evaluated both by these people and other independent designers. The results of the evaluation are generally positive."