1. A knowledge system comprising a computer having a memory storing a knowledge base, said knowledge base including predefined descriptions of assemblies of predefined components for indicating whether a specified component is permitted in a specified assembly, and for at least some of said descriptions of assemblies, sets of predefined conditions of different properties of the components in the assembly for indicating whether certain predefined properties of a specified set of components are compatible within the assembly, said memory comprising a control procedure for first obtaining a predetermined initial set of predefined components, thereafter matching the initial set of components to the predefined descriptions of assemblies to determine respective sets of matching components including the components in the initial set which are also permitted in the respective assemblies, thereafter applying the sets of conditions to the respective sets of matching components for the respective assemblies, and indicating whether the respective conditions are satisfied, said computer including means for executing said control procedure to thereby first obtain said predetermined initial set of predefined components, thereafter match said initial set of components to said predefined descriptions of assemblies, thereafter apply said sets of conditions to the respective sets of matching components for the respective assemblies and generate an indication of whether the conditions are satisfied.