Abstract: An object-oriented decision structure usable by different diagnostic software engines defines a knowledge base that includes a problem, a symptom of the problem, a solution, and case in which the solution is the solution to the problem. The data structure includes a question object defining a question, a response object defining an answer, a question node object, a solution node object defining the case, a case master object defining the problem, the solution, and the case, and a symptom object defining the symptom and pointing to the case master object and to the solution node object. The question node object points to the solution node object, the question object, and the response object and correlates the question, the response, and the solution node object, and the solution node object points to the case master object.