A knowledge based computing system is authored using a directed graph presented to the author at an authoring time. The directed graph has one or more question nodes and one or more answer nodes. The question nodes and the answer nodes connected to one another on one or more paths by links between each of the question nodes and each of the answer nodes so that question nodes and answer nodes alternate as the path is traversed in a path direction so that a "QA directed graph" is created. Each question node associated with a question data structure and each answer node associated with a answer data structure that are populated with information accessed from the author using question and answer templates associated with respective question and answer nodes on the QA directed graph. After the expert system is created (authored) using the QA directed graph it can be run at a run time to provide and access information from a service user. The system has many applications particularly in the health care and teaching fields.