The role of technological forecasting is not merely to predict "what will happen and when", but is to aid R \& D planning and management in peering into the future. Although Delphi survey technique has been found quite useful for long-range technological forecasting, from the user``s point of view (such as R \& D planners and project managers), the conventional technique applied to predict occurrence dates of closely related future technology developments has a major shortcoming. Namely, the Delphi result can be used only in exploratory forecast by individual base. Since the technique does not consider the significance of relationship and interaction between developments, its result can not be interpreted easily in normative aspect of forecasting, i.e., impact analysis associated with user``s planning context, or simulation work under various condition regarding R \& D policy or plan. Moreover, existing supporting tools concerned with interaction, e.g. Cross-impact analysis, requires the burdensome explicit information on interrelationships. This study, following the line of Cross-impact analysis, is concerned with the interrelationships among technology developments over time horizon, but seeks to avoid imposing any additional burden. Instead, it utilizes the information apparently skipped in the original Delphi survey data, by adopting a knowledge-based system approach. From the user``s point of view, the Delphi data can be considered extensive knowledge of experts on a specific domain, spending much time and cost. It will be useful to convert one-time forecast of the Delphi into a knowledgebase of decision support system(or expert system) and to refer to the experts`` knowledge-base at instance when a user has his own information or situationspecific evidence. To construct a knowledge-base with focus on interrelationship, knowledge representation and acquisition scheme is required. And it should be designed to describe the real forecasting domain, i.e. techn...