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Relational Modeling
    Digital Design Studio (CAAD Futures '89) ed McCullough, Mitchell, Purcell 1990
    Relational modeling is a simple and powerful extension of parametric design that overcomes this weakness. By viewing relations as reversible rather than one-way, any set of properties can be chosen as input parameters. For example, a relational model that calculates the shadow length of a given building can also be used to calculate the building height given a desired shadow length. In exercising a relational model the designer is not limited to a pre-selected set of input variables but can explore and experiment freely with changes in all parts of the model.

    Co is a relational modeling environment under development on the Macintosh-II computer, and Co-Draw, a prototype CAD program based on Co. Co?s relational engine and object-oriented database provide a powerful basis for modeling design relations. Co-Draw?s interactive graphics offer a flexible medium for design exploration. Co provides tools for viewing and editing design models in various representations, including spreadsheet cards, tree and graph structures, as well as plan and elevation graphics. Co?s concepts and architecture are described and the implications for design education are discussed.