A relational database is for relating maintenance information that differs for each of a plurality of complex systems, such as a plurality of differing aircraft, using a common database structure so as to facilitate maintenance procedures for the plurality of complex systems. The database structure comprises: a plurality of primary entities for providing a fault model description of each of the plurality of complex systems, the fault model description including, for each of the plurality of complex systems, failure modes, symptoms and data required to effect a repair; and a categorical entity corresponding to a complex system, such as an aircraft, that enables selection of the fault model description corresponding to the complex system or aircraft. The relational database is particularly suited for use in or by an aircraft maintenance and diagnostic system that assists with fault correction for a fault condition within an aircraft based on a fault model for the aircraft.