Form and Substance in Physical Database Design: An Empirical Study

As with many complex design problems, physical database design is difficult, ill-structured, and highly human intensive. In order to effectively construct support systems or improve the practice of database design, it is important to understand how human designers reason about the task. We report an empirical study of physical database design problem solving. Thirteen subjects each solved two physical database design problems: five subjects were experienced designers; eight were graduate students with little or no actual design experience, though they were exposed to the principles of design through course-work. For each problem, subjects were presented with a list of available problem information (hardware, content, and activity data) and were directed to generate a physical design (record structures and access paths) that would minimize retrieval time and storage space. All sessions were audiotaped. Three types of data were incorporated for the analysis: information acquisition patterns, solution generation patterns, and verbal protocol. It was hypothesized that database design reasoning embodies forms of deliberation to reduce problem-solving complexity and that these forms resemble those found in other design problem-solving studies—commonality of task environmental demands will result in commonality in problem-solving methods in response to those demands. In particular, we expected to find specific control strategies, the use of hierarchical abstraction, the use of problem-specific heuristics, and the use of qualtitative reasoning with mental models of dynamic components of the task. Our results indicate that these forms are indeed present and of significant value in physical database design problem solving. Experience played a significant role in determining both the form and substance of reasoning used in physical database design. Both experienced and inexperienced database designers exhibited at least some of these forms of reasoning. Experienced designers, however, effectively applied these forms, demonstrating a substance of reasoning, although their methods of application varied considerably. The least experienced designers did not effectively apply these forms and, lost in the detail of the design problems, were unable to generate reasonable designs. It is concluded that recognition of appropriate reasoning forms and the effective application of these forms are critical to developing efficient physical database designs. The implications of the findings are discussed.