ALTERNATIVE FUTURES ANALYSIS USING G.P.S.S. THE GENERAL PURPOSE SYSTEMS SIMULATOR IN MANAGEMENT

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1 James G. Janossy City of Chicago Datacenter CL-54 Richard J. Daley Center Chicago, Illinois ALTERNATIVE FUTURES ANALYSIS USING G.P.S.S. THE GENERAL PURPOSE SYSTEMS SIMULATOR IN MANAGEMENT ABSTRACT. The digital computer has progressed from a specialized "calculation engine" to ah extremely powerful tool for non-traditional forms of analysis. Discrete event simulation of organizational processes is now fairly easy to perform, using higher level computer programming languages. Using one such language, the General Purpose Systems Simulator (GPSS), this study illustrates how a model of a land use regulatory agency was created and used to determine a means to increase its efficiency of operation. Of particular concern and coverage is the graphic presentation of simulation results to managerial decisionmakers, and the cost-benefit analysis of these findings. COMPUTERS, SIMULATION, AND DECISIONMAKING The digital computer, the single most familiar symbol of modern technology, came into existence in the late 1940's and has been greatly improved since that time. While the first computing machines were of limited capacity and operated at a snail's pace by modern standards, the 19's saw the introduction of computing equipment large enough and fast enough for widespread commercial and scientific application. A consequence of the computer's increasing capabilities has been the blossoming of analytical techniques previously not practical. One of the most Intriguing of these is the discrete event simulation model. Once such a model is created, using measurements of a real life situation, it can be "operated" by a computer based on the generation of random numbers. These numbers, given meaning by the structure of the analytical model, are interpreted to signify the outcome of decisions or other occurrences. It is possible to simulate the operation of industrial systems, network usage, or organizational processes in this manner, by allowing the computer to very rapidly imitate them. Of great utility is the ability to predict the effects of changes on the real life situation by watching what happens when these changes are introduced in the computer model. Simulation in this form has been understood prior to the development of the computer, but it was not feasible since even a modest model might require the selection and Interpretation of several hundred thousand random

2 number derived events. The General Purpose Systems Simulator language, or GPSS, is one of a number of specialized tools which allow speed and flexibility in creating automated simulations. In the spectrum of computing languages, GPSS is a higher level language that is, it causes more to be done with every program statement and it is more specialized than PL/I, COBOL, or FORTRAN, which are more common general purpose programming languages. The use of GPSS for the analysis and optimization of traffic flow, communication networks, and industrial processing systems is now a well developed art. The maximization of organizational as well as individual employee productivity is of paramount concern to the maintenance of a vigorous economy. Reliance on newer analytical methods such as simulation can foster the development of more efficient organizational processes and creative new approaches to the provision of private and public services. A SIMULATION ANALYSIS CASE STUDY This study employs an automated simulation to analyze the alternatives available to a public agency in reducing backlogs and delays in the zoning administration process. The analysis sought to identify changes in the process which would reduce the length of time it takes for applications for land use development to pass through a review and public hearing "system" and be approved or denied. The impact of these changes on the backlog and application processing duration was to be identified as quantitatively as possible. This analysis begins with the identification of the "processing system" and the structuring of a model of it based on the examination of actual application handling. The system depiction is then transformed into an automated model using GPSS. Once the GPSS model is operational, the identified changes are introduced into it and their effects noted. The feasibility of changes which appear to contribute to desirable effects is judged using cost-benefit analysis. The change which appears most economical and effective is recommended to managerial decisionmakers in graphic as well as summarized narrative form. Case study background Zone variances and conditional use permits are two similar forms of adjustment of the legally allowed use of real property. Zoning ordinances define the land use permitted for individual parcels of land, and set development standards such as minimum buildable lot size. The ordinance applicable to this study provides a means for the adjustment of certain development requirements, based on the application of the property owner

3 In the jurisdiction for which this study was performed, applications for zone variances and conditional use permits are accepted and processed by a unit of ten personnel, eight of whom are professional land use planners. These personnel develop the required background reports, maps, legal notifications, and other materials necessary for consideration of the application by the planning commission. At the time this study was conducted, applications for approximately 320 zone variances and conditional use permits were being filed annually. Over ninety cases were awaiting processing, and the average time between the filing of an application and its approval or denial was seven months. This study was conducted to Identify a way to speed zone variance and conditional use permit application processing. Defining the system Defining the system to be simulated is the most critical task associated with the development of any simulation model. To construct a model of this or any other processing mechanism, it is necessary to trace the actual sequence of steps and procedures involved. This process is similar to the "systems analysis" which is conducted when a function is to be automated, and results in a step by step "flowchart" of actions and decisions. During this development phase, clarity is emphasized in: 1. The identification of all possible processing actions; 2. The elimination of "steps" which are in fact comments, directions, or descriptions, but not processes; 3. The elimination of attempts to make the chart indicate a time factor through the use of time/length chart scale or other device. Development of a GPSS model GPSS was designed to simplify system simulation. The language provides "blocks," each of which is one program statement, to represent roughly one step of a system flow chart. "Transactions" are created by a random number-based "event generator" and are sent into the series of blocks in the same manner that customers or cases originate and proceed through a real-life system. A range of "transit times" or processing times in steps can be specified by the user in a number of ways. Instructions can be placed at any point to measure the size of "waiting lines" or queues of customers or other quantities represented in the system. Decision trees can be represented by sequential "transfer" blocks which provide loops or branches in the routes that transactions follow. In short, GPSS allows a simulation to be set up almost directly from a processing system flow chart. In order to complete the GPSS model, as detailed an understanding as possible of the time duration of each individual step of case handling was also needed, as well as an understanding of the variability of this duration from case to case. The combination of recorded information (where available), staff interviews,

4 and statistical sampling of actual cases, was used to develop data. this The system flow chart for this study comprised approximately sixty processes and decision points. The GPSS program based on this flow chart was written with 119 statements. This model was used to produce 126 weeks of simulated operation in less than one minute of computer run time. Major processing system status reports were developed at simulated 18 week intervals, while an indication of the case backlog was called for weekly. A total of 48 computer runs were made, testing various combinations of increased application processor caseload, zoning board agenda size, case filing rate, and organizational changes. SIMULATION RUN RESULTS The product of a GPSS simulation is a tabulation of statistics requested by the user. These can take the form of measures of backlogs, the transit times of items between various points in the system, and frequency distributions of process durations. In some GPSS installations, crude printer bar charts may be obtainable. These raw products in and of themselves are almost always less than acceptable to managerial decisionmakers, since the tabulations are voluminous and it is difficult to "see the forest from the trees." These products demand interpretation and presentation in succinct graphic form. FIGURE 1 MODEL-PROJECTED BACKLOG ALTERNATIVES OVER TIME

5 Figure 1 indicates the projected result of the continuation of the current application processor caseload of six, as well as the anticipated results with greater caseloads. Of significance here is the length of time which the model shows is required by the increased caseloads to effect any reduction in the case backlog. For example, the simulation shows that even with a 33% increase in caseload, from six to eight cases per processor, a full year would have to elapse before the case backlog would disappear. This finding alone resolved a dispute between a deputy planning director, the planning commission, and the metropolitan government's budget office, as to why sporadic additional sessions of the zoning board seemed to have no effect on case backlog. Figure 2 presents a picture of the case processing duration and zoning board agenda size with existing caseloads, case filing FIGURE 2 MODEL RESULTS WITH CASELOAD OF 6 Time (weeks) Backlog (cases) Duration (months) Agenda Size (cases) i I i i i i I 1 5 I 10 I I I I I I I 'IT I~T t j I tl Li ti I,

6 rate, and an existing zoning board agenda length limitation. In keeping with the slowly growing case backlog, total case processing duration would increase. This can be said based on intuition; the simulation gives us a quantitative measure which can be graphed. Figure 3 illustrates what could be anticipated by a combination of increasing caseload per processor from six to eight cases, and allowing the zoning board agenda to fluctuate in response to actual need. Case processing duration for over half of the cases filed would likely decline from seven months to four months in about one year. During this time, the zoning board would hear an average of eight or nine cases per weekly session. Within sixteen months, case processing duration would drop to three months for the bulk of applications. Three months is the minimum case FIGURE 3 MODEL RESULTS WITH CASELOAD OF 8 (OPEN AGENDA LENGTH) Time Backlog Duration (weeks) (cases) (months) Agenda Size (cases) rrr I i i i r n 1. ii... : % z 5 10 I I I.h - r i - hi L JE c 72 2 T li i I l l l h h

7 processing time, given the steps which make up this "system." While no simulation model can be absolutely predictive, the perspective gained by some reasonably founded quantification of alternative actions and their ramifications adds measurably to the decisionmaker's perceptions. In response to requests from the organization under study, the model was also modified to provide multiple runs using increasingly faster case generators. The change made to accomplish each different "filing rate" run consisted simply of altering the parameters on the GPSS program "case generator" card image. As one would expect, "disaster" is approached more rapidly with each case filing rate increase if the present caseload of six cases is maintained. At the fastest rate tested, representing a 21% case filing rate increase, the backlog would appear to grow by % in the first year. Judging alternatives cost/benefit implications In order to render a useful conclusion to an analysis effort such as this, it is necessary to gauge proposed changes against some criteria, and recommend a course of action. Ordinarily, in a business setting the development of a cost-benefit study to meet this need would include the projection of increased income accruing from any change, in comparison with the cost of making the improvement'. In the public setting in which the agency under study operates, it is not usually possible to place a dollar value on the "benefit" accruing from service improvements. However, means do exist to approximate cost-benefit criteria. While acknowledging the limitations of the approach, it is possible to "satisfice." That is, let us assume that we are provided information from a study such as this on the likely outcome of a range of processing changes. Absent any extraordinary complaints about poor service, our main desire would be to either: 1. Improve the service level at no additional cost, or 2. Maintain the same service level with the use of fewer resources, or 3. A combination of the above. We could reasonably take as one cost-benefit criteria the approach that only those processing changes which result in service level improvements without any additional cost will be acceptable. If there do exist extraordinary shortcomings in the present level of service, which might have precipitated the use of an analytical tool such as simulation in the first place, "satisficing" may include some margin for the infusion of additional resources. The magnitude of this margin would likely be the amount of resources which a "seat-of-the-pants" solution attempt would demand; in other words, the amount of resources which would be consumed by a solution less founded on a research technique and based more on simple judgment. In the case of the processing situation described, this reasoning would lead to a cost criteria

8 that allowed an Increase In expense up to the amount demanded by one additional professional case processor. The provision of an additional case processor to the processing unit would probably be the first step ordinarily taken to try to improve the service level. In fact, this was a change already requested by the agency as a part of budgetary review. The margin of cost taken as the criteria to judge the acceptability of any processing system improvement was therefore $22,0, the total salary and employee benefit cost of this additional position. Resolving the case study problem Based on the results of the simulation modeling study conducted, and with consideration of the described cost-benefit criteria, it was recommended that steps be taken to persuade the FIGURE 4 MODEL RESULTS WITH CASELOAD OF 7 (OPEN AGENDA LENGTH) Time (weeks) Backlog (cases) Duration (months) Agenda Size (case*) 'III ii: t i. i : : z % z : so : = % = r r n "I li HI Z % Z la 1L L i i It i

9 zoning board to raise its regular agenda size limit to seven cases, and to elicit the agreement of that board to hear up to ten cases per session when that great a number coincided for presentation. Processing unit caseload would then be increased to seven cases per processor, and support services such as mapping and clerical work monitored to determine if problems arise in meeting hearing dates. Personnel working in these areas would be advised of that while these changes will ultimately improve the case processing time, the changes would not produce significant results for over one year. Figure A indicates the results which could be expected from these coordinated actions. In one year, the processing duration on the majority of cases would have been reduced from seven months to five months, and case backlog would have declined %. At a point two years in the future, approximately 80% of cases would be disposed of in three to four months handling time. Zoning board agenda size would vary from five to nine cases per session. Should efforts to increase the agenda length of the Zoning Board fail, it was recommended that a second regular weekly session of this board be arranged, increasing the size of the total weekly agenda to twelve cases. Processing unit caseload would then be increased to seven per processor, and additional support service measurements instituted. Under the first course of action, the anticipated improvement in case handling time would require only the slightly faster expenditure of consummable case preparation materials, since case processor reassignments would allow absorption of one additional case per processor. If, however, the second course of action was necessary, it would appear that this would still be a feasible and economical method of coping with the backlog, since the second session of the Zoning Board would incur an annual cost of approximately $10,000, based on the extra per-meetlng compensation of its participants. Simulation analysis clearly infers that the simple allocation of an additional professional case processor cannot move this system in the desired direction. Since provision of an additional case processor would only increase the caseload capacity of the processing unit, cases would bottleneck to a greater degree at the point of Zoning Board consideration. It is likely that as this occurred, sporadic additional sessions of the Zoning Board would be scheduled, but these would not provide sufficient agenda capacity to improve the backlog situation. In time, individual caseloads would probably then be adjusted downward. The net effect of the allocation of the additional case processor would in time have been to decrease the productivity of the processing unit, without alleviating the backlog condition. Such a decrease in productivity would be undesirable

10 It was particularly noteworthy in the application of the simulation modeling technique to an organizational system problem, that the "common sense" approach of the allocation of more personnel was shown to be counter productive. The use of the simulation model provided insights to "alternative futures" possible with adjustments in existing procedures. The graphs of processing system performance under various caseloads and case filing rates materially assisted the organization in achieving an understanding of the outcomes it could anticipate. These products were instrumental in reaching a consensus among system participants concerning a course of action to resolve the case handling problem. SIMULATION ANALYSIS AND ALTERNATIVE FUTURES DECISIONMAKING Management in public and private organizations is an activity synonymous with the selection of a course of action from a range of alternatives, and of the making of decisions as to "what will be done." The range of such decision making includes the choice of new products and product lines, the location of new plants and stores, the choice of procedures to be used in a process, and so forth. Tools which can assist managers to select the best of available options, or to creatively identify options which were not previously thought to exist, are valuable tools. In the field of industrial engineering, Taylor-oriented time and motion studies have long been used to pinpoint the minute increments of labor which, taken together, contribute to the efficiency of a given process. While these basic techniques have proven their applicability to routinized operations, it is interesting to note that they are orders of magnitude less comprehensive than simulations. The former techniques address the question of "doing what you are doing, better." The latter, when properly applied, deal with the issue, "What do we do?" It is in this sense that simulations can be of benefit to management. The application of the simulation technique, made possible by the refinement of specialized computer programming languages and increasingly convenient access to modern computing machinery, allows the development and "testing" of alternative choices in specific situations. It makes possible, through graphic presentation of the tradeoffs involved in these choices, the identification of the "best" choice in various situations, not as a dictate but as a guide to managerial decisionmakers. MORE ABOUT GPSS This presentation is a synopsis of a published case study entitled Alternative Futures Analysis Using GPSS -- The General Purpose Systems Simulator in Management,available from Creative Decesion Systems, 659 Oleander Dr., Los Angeles, CA for a small fee