One of the purposes of analyzing the business domain is to reveal the background of customer requirements. The resulting artifact provides us the reason why the requirements arise and possibilities of other useful solutions to solve the customers? problems. We?ve developed RODAN as a business domain analysis method. RODAN improves the understandability of the background of the requirements by focusing on roles in the business domain and owners of the business goals. This paper is an attempt towards clarifying the notion of understanding the business domain and evaluating the method effectiveness of extracting undefined requirements and rationales of defined requirements.