SIBYL/TFS: The Total Forecasting System
Spyros Makridakis · The American Statistician · 1981
SIBYL/TFS is a single set of programs that takes into account recent advancements in computing capabilities and recent changes in attitudes toward forecasting. The system therefore provides decision and policy makers with a means of realistically dealing with forecasting issues in today's environment. The basic principle behind SIBYL/TFS is that the programs provide an effective and efficient means of meeting everyday forecasting requirements through the combination of the better aspects of both interactive and batch computing systems. This has been achieved by introducing three different modes of operation: Interactive, Mixed (i.e., Interactive/Batch), and Batch (see Table 1). The Mixed mode has two variations, one in which the standard questions are not asked, and one in which the user specifies which questions he or she wishes to be asked by the program. Not only does the user of SIBYL/TFS have the choice of either of these variations, but the user can also prepare interactively answers to questions for the Batch mode and have these responses stored for use in subsequent runs. In addition to operating in any one of these three modes, the user can also choose between three levels of expertise (beginner, intermediate, or advanced); and can request a detailed output or a short one, in which all important output, with a graph of the latest actual values and forecasts, is printed on a single page. Questions and explanations are given in either English or French, and other languages will most likely be added eventually. SIBYL/TFS is a command-driven system designed so that further forecasting methods or routines can be added at will. The system offers help to the user each time the return key is pressed (without an answer being entered), and it accepts only those responses that are within the permissible range. Furthermore, SIBYL/TFS includes many utility routines that indicate possible errors in the forecasts, allow the user to adjust his or her results, and incorporate tracking signals that will provide advance warning in the event that the forecasting process begins to go out of control. SIBYL/TFS can be run on a CRT, thus avoiding the use of slower hard-copy terminals. All important results are saved in a file that can subsequently be edited and reproduced on a high-speed printer. The forecasts are easily used as an input for production or inventory systems, since forecasts, together with confidence limits, are stored in files that have been designed for this purpose. SIBYL/TFS is written in FORTRAN and presently operates on a DEC 20/20 computer system. Adaption to most major computer systems is anticipated, and it is planned that the programs will become available on major time-sharing networks.