We regard conceptual design as a negotiation between what we believe and what we observe. This process is not necessarily goal-directed, but establishes new connections between observables that become useful in product design. We propose an agent-oriented modelling method that can represent observation and experiment more effectively than conventional computational models. Our computer model is a metaphor for a physical prototype with which many design agents can interact from different perspectives. In this way we relate conceptual design to the coordination of experimental activity in the concurrent engineering process.
Our models make use of special-purpose definitive scripts, which permit synchronised update of variables: a generalisation of the spreadsheet principle. The definitive scripts are implemented in the environment of the Abstract Definitive Machine which provides an operational interpretation of the scripts. The use of these tools is illustrated with reference to the design of a model railway layout.