Integrating Case-Based and Model-Based Reasoning: A Computational Model of Design Problem Solving

My Ph.D. dissertation (Goel 1989)1 presents a computational model of experience-based design. It first reviews the core issues in experiencebased design, for example, (1) the content of a design experience (or case), (2) the internal organization of design cases, (3) the language for indexing the cases, (4) the mechanism for retrieving a case relevant to a given design task, (5) the mechanism for adapting a retrieved design to satisfy the constraints of the design task, (6) the mechanism for evaluating a design against the specification of the design task, (7) the mechanism for redesigning a failed design, (8) the mechanism for acquiring new design knowledge, (9) the mechanism for chunking information about a design into a new case, and (10) the mechanism for storing a new case in memory for potential reuse in the future. It then proposes that decisions about these issues might lie in the designer’s comprehension of the designs of artifacts he/she has encountered in the past, that is, in his/her mental models of how the designs achieve the functions and satisfy the constraints of the artifacts. To elaborate and evaluate this proposal, the dissertation analyzes the design of physical devices such as simple electric circuits, heat exchangers, and angular momentum controllers. It develops a theory of designers’ comprehension of device designs in terms of functional models of how devices work. The functional model of a device provides a causal explanation of how the structure of the device produces its functions. The dissertation then describes how the theory of functional models gives and guiding the simulation of the modified design in the evaluation phase. Based on Bylander and Chandrasekaran (1985), the dissertation adopts a component-substance ontology of physical devices. In this ontology, the device-independent functions of primitive components of the domain are viewed in terms of their interactions with abstract substances. The structure of a device is viewed as constituted of components, substances, and relations among them; the behavioral states of the device are viewed in terms of the properties of substances and components at specific points in the device space and time; the intrinsic functions are viewed as transformations from one behavioral state to another; and the causal behaviors are viewed as a sequence of behavioral state transitions that compose the interactions among the components and the substances in the device structure into the functions of the device as a whole. The second step in the development of the functional model focuses on its organization. The dissertation presents a behavioral representation language for organizing the functional rise to principled answers to many basic issues in case-based design. It also describes the KRITIK system, which instantiates and simulates this computational model.2