A century ago the physician had too little information on which to determine accurate diagnoses. Due to the rapid progression of technology in the Twentieth Century and the beginning of the Twenty-First Century, this situation changed significantly. Now the physician is faced with multi-parameter analyses that include sophisticated imaging, advanced cardiovascular studies, extensive laboratory tests, and genetic information, all of which impact diagnosis, treatment, and prognosis. New informatics tools are needed to assist, not replace, the physician in the decision process. Decision analysis tools must be flexible to accommodate new methods of diagnosis as well as advances in information technology. In this article, basic structures are defined that can form the basis of such a system.