A knowledge-based input preprocessor for building system simulation programs was developed at the National Bureau of Standards for the modular, dynamic building and HVAC systems simulation program HVACSIM+. The complexity of the HVACSIM+ program requires the user to have extensive knowledge of all the inputs, outputs, and parameters required by each component module in order to set up a data input file that will correctly link the multiple inputs and outputs of the user selected component modules from the HVACSIM+ library. The data input process a very tedious and time-consuming. This paper describes the development of a front-end program to generate the required data to link the multiple inputs and outputs of the user selected component modules. A microcomputer based language, Prolog, was used to program the data base of the input and output requirements of each component module in HVACSIM+ and to perform correct kinking of those variables. A data base editing program was developed that would delete, insert, and re-link a component module in an already generated data file.