||New media throughout history have passed through a period of transition during which users and technologists took many years to understand and exploit the medium's potential. CAD appears to be passing through a similar period of transition; despite huge investments by vendors and users, CAD productivity remains difficult to achieve. To investigate if history can provide any insights into this problem, this thesis begins with an examination of well-known examples from history. The analysis revealed that, over time, users had developed efficient strategies which were based on powers and limitations of tools; delegation strategies exploited powers provided by tools, and circumvention strategies attempted to overcome their limitations. These insights on efficient strategies were used to investigate the CAD productivity problem based on four research questions:
1. How do architects currently use CAD systems to produce drawings?
2. What are the effects of current CAD usage on product and performance?
3. What are the possible causes of current CAD usage?
4. What are the capabilities of the CAD medium and how can they be used efficiently?
The above four questions were addressed through the qualitative, quantitative, and cognitive analysis of data collected during an ethnographic study of architects working in their natural environment. The qualitative and quantitative analysis revealed that users missed many opportunities to use strategies that delegated iteration to the computer. The cognitive analysis revealed that missed opportunities to use such delegation strategies caused an increase in execution time, and an increase in errors many of which went undetected leading to the production of inaccurate drawings. These analyses pointed to plausible cognitive and contextual explanations for the inefficient use of CAD systems, and to a framework to identify and teach efficient CAD strategies. The above results were found to be neither unique to the CAD domain, nor to the office where the data were collected. The generality of these results motivated the identification of seven claims towards a general theory to explain and identify efficient strategies for a wide range of devices. This thesis contributes to the field of architecture by providing a detailed analysis of real-world CAD usage, and an approach to improve the performance of CAD users. The thesis also contributes to the field of human-computer interaction by demonstrating the generality of these results and by laying the framework for a general theory of efficient strategies which could be used to improve the performance of users of current and future computer applications.