Engineering designers often generate design concepts based on a functional understanding of the problem. Many engineering textbooks encourage designers to abstract the essential problem to a higher-level functional representation of the product and subsequently develop solutions to the functional needs. However, a functional perspective of design does not provide a complete view of what the product must do and how the product must interact with users and other parts. To address this, an alternative modeling approach has been developed to complement the traditional functional modeling approaches. Two such approaches include (1) activity modeling to capture the user actions from production through death of a product, and (2) affordance-based design to capture a range of characteristics of a product. There exist opportunities to combine function based and interaction based modeling approaches to an integrated model. Additionally, there is not sufficient experimental data to support the use of such model during the early stages of design.;Thus, the primary objective of this research is to understand the role of functions and interactions in describing a product. In order to accomplish this, two design experiments was conducted: (1) a user study to compare the effect of function models and function interaction models in aiding the designers to develop creative concepts and (2) a card sorting exercise to understand whether users categorize products that are in the market based on the product's functionality or user-product interaction. In the user study, forty graduate and senior level students are divided into two groups and asked to develop concept sketches using either the function model (FM) or the function interaction model (FIM) they received. The sketches are then statistically analyzed in terms of quantity and quality. The findings from this study suggest that FM enables designers to develop more number of concepts compared to FIM. However, the quality of the sketches developed by the designers at the concept level is found higher for the FIM. There is no significant difference in the quality of sketches at the requirement level developed using the FM and the FIM. In the card sorting exercise, fifty-three sophomore level engineers categorized consumer products based on the product's functions and interactions at two levels (low and high). Analyses of the results indicate that users are comfortable classifying products that are either simple (low functionality-low interaction) or complex (high functionality-high interaction). Initial results from this card sorting exercise also suggest that functions of a product get priority over the interactions it has with the user.
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