Proceedings of INFORMS First Conference on Information Systems and Technology, May, 1996 DESIGN AND EVALUATION OF A BUSINESS INFORMATION VISUALIZATION SYSTEM FOR MANUFACTURING PRODUCTION PLANNING SUPPORT Ping Zhang School of Information Studies Syracuse University pzhang@mailbox.syr.edu Peng Si Ow Consultant Austin, TX Andrew B. Whinston Department of Management Science & Information Systems The University of Texas at Austin abw@uts.cc.utexas.edu Abstract In most management domains, problem-solving and decision-making are overwhelming because of the high volume of complicated data, the multiple complex relationships among data, the negotiability of the constraints, the changing environment, and time pressure. Most existing computer systems, such as expert systems, decision support systems, and simulation systems, have built-in functionalities and cannot reflect the changing environment and possibilities for negotiation. Although they can generate reports, they are very limited in providing superior solutions for complex problems. Human beings are in control in the process of problem-solving and decisionmaking. A useful decision support system should incorporate human problem-solving processes, support human information need during the processes, consider human cognition and perception characteristics, and provide insight into generated or collected data. This paper describes our preliminary results on the design and evaluation of an information visualization system for the support of manufacturing production planning. It introduces the domain problem, information visualization research methodology from a usercentered perspective, and the design and implementation of a prototype system based on a proposed visualization model that emphasizes human-information interaction. A lab experimental study shows that the visualization system cooperated with planners’ problem-solving strategies, provided the relevant information at the relevant abstract levels that planners need during the planning processes, and was easy to understand and use. Compared with a traditional manufacturing production planning support system, the visualization system supported planners with more alternative solutions, more efficient changes in raw planning data, more confidence about domain tasks, and more satisfaction with solutions. (Visualization of high-volume, multi-dimensional, non-geometric-based managerial data; Humaninformation interaction; Manufacturing production planning; Decision-making support) Introduction Recent advances in technology have enabled the development of sophisticated graphical user interfaces for the visualization of large quantities of data [12, 15, 16] that are either gathered from the real world and analyzed by a computer or produced through computer simulations. The word "visualization" has helped clarify what some people for years have called "computer graphics." It means using computer-generated graphics to help people understand and clarify visually the relationships inherent in data [16]. The information conveyed to a viewer by visualization undergoes a qualitative change because it brings the eye-brain system, with its great pattern-recognition capabilities, into play in a way that is impossible with purely numeric data [7]. Proceedings of INFORMS First Conference on Information Systems and Technology, May, 1996 Until now, most uses of this technology have involved the visualization of systems that are naturally represented as two- or three-dimensional objects. Examples can be found in many scientific visualization applications, such as visualizing biological molecules, medical imaging, or tracking and imaging elementary particles. However, many of the most exciting potentialities of visualization technology involve the visual representations of non-geometric-based data that do not have physical-based interpretations or geometric structures that lead directly to computer-supported representations. This type of data can be easily found in many business domains. Efforts have been made to visualize business information: Shneiderman et al. [9, 17] developed TreeMaps to visualize huge amounts of hierarchical and categorical information such as file directories, budgets, sales data, and organizational structure data. Chris Jones [10, 11] used attributed graphs and graph-grammars for representing management science models such as decision trees, linear programming, and critical paths that involve network-related relationships. However, most management domains have data with complicated relationships that are difficult to interpret as hierarchical or network data. Manufacturing production planning is such a domain. Manufacturing production planning involves large amounts of detailed data and the need to manage a large number of complicated relationships and flexible constraints. Solutions provided by expert systems or other computer systems are not adequate to deal with such a dynamically changing environment and the flexibility for negotiations. Visual interactive simulation for modeling [2, 3, 8], although it “uses a simulation model where the user can suspend execution of the model, modify one or more parameters, including the model structure, and resume model execution,” still requires the model to capture a limited number of parameters in advance and cannot reflect the changing environment and negotiability. Human decision-making in such a domain becomes overwhelmingly complex. Even with some support of existing computer systems, people still have to use their cognitive powers to figure out the “stories” behind the computer-generated reports, which could be as long as several hundred pages. An effective solution to this situation is to shift some of the user’s cognitive load to the human visual-perception system: we let people see -- perceive visually -- what they need to “see” -- perceive cognitively -- so that they do not have to puzzle it out otherwise. The potential benefit of visualization for providing planners with insight into the complexities of non-geometric information in the manufacturing planning process is significant. However, it is far from obvious how to visually represent the interaction of the many factors that influence the production processes in a manufacturing plant in a way that will enable production planners to make better management decisions. This paper describes the preliminary results of our research on the development of a visualization-based decision support system for manufacturing production planners. It introduces the domain problem, visualization research methodology, the design and implementation of a prototype system based on a proposed visualization model, and evaluation results of the prototype system using graduate students in a lab experimental study. This research is part of our longterm project on discovering laws for human-information interaction and developing information visualization methodology and techniques for problem-solving and decision-making in business domains [22]. Manufacturing Production Planning Problems In a collaborative effort with IBM Austin, Texas, we studied the production planning problem at the IBM PC Co.’s electronic card assembly and test plant (ECAT). In production planning, specifically manufacturing resource planning, a planner’s goal is to maximize overall revenue from the production, subject to resource constraints such as tools, manpower, and component availability. ECAT has more than 200 types of products and more than 2000 types of components. Some of the components are shared by multiple products. There are a total of six independent assembly lines (also called production pull lines -- PPLs); each of which has its own production capability but also contributes to the entire factory. The production planning is done monthly. The production plan rolls 12 months' horizon with varying levels of detail. The decision-making environment at ECAT is very dynamic. There is a severe component shortage problem. Most of the shortfall components can be obtained by negotiating with suppliers. The price market for the end products -- personal computers -- is very competitive. Sometimes the planner has to make a decision between keeping market-share by paying high prices for shortfall components, which may hurt profits, or keeping high profits, in turn may hurt the marketshare. Also the planner has to decide if some products will be produced outside (outsourcing) instead of by the plant. In such a dynamic environment, the planner’s understanding of the planning problem situation is crucial. During the planning period, the planner has many possible actions to take in order to solve some of the Proceedings of INFORMS First Conference on Information Systems and Technology, May, 1996 problems or sub-problems. For instance, s/he can move products to different assembly lines, move products to different time periods, change an assembly line’s capacity, change the quantity of products to be made (demand), change the quantity of components available (scheduled receipts), and change the distribution of components over products (production mix). Planners usually have three kinds of difficulties when doing the production planning or adjusting an existing plan in response to changes in the environment: recognizing potential conflicts, coordinating conflicts, and evaluating adjustments [14]. There are existing planning tools available in ECAT. One of them is ESIT, an optimization model based on IBM's commercial product MPSX. Another one is Copics: a batch-processing production planning system based on MRP process that runs on an IBM mainframe. It provides a texture interface, has a central database, can generate a few reports, and handles capacity and component planning separately. Due to the unfriendly user interface of Copics, Sorcerer [1] has been developed under the PS-2 environment. It provides a spreadsheet-like interface for Copics, and allows the planner to interactively change the data and do what-if analysis. The planners feel that the dynamic nature of the decision-making environment makes it impossible to use ESIT: the planning constraints and possible actions cannot be represented easily in the algorithmic system. Although Sorcerer has a friendly user interface and simple one- or two-dimensional graphs such as line charts, bar charts, pie charts, etc., the data it can provide are basically in tabular format: they are either limited to the size that a computer screen can handle, or printed on a report that may be several hundred pages long. The planners' primary frustration is trying to hold these vast quantities of information while trying to develop a solution. This presents an obvious opportunity for enhancement of the planning process through computer automation and visualization that can shift some of the planners’ mental load to their perceptual system. Research Methodology Our approach to the visualization of planning data is oriented around the planners' problem-solving process modeled by Newell and Simon [13, 18]. A general problem-solving process has the following stages: identifying the problem, generating alternatives, evaluating alternatives, and choosing solution(s). Consciously or unconsciously, a planner may iterate among the stages until the problem is solved. The application of Newell-Simon’s model to solving a problem results in a domain problem space. Figure 1 shows the production planning problem space. A 12month plan can be broken down into a first-12-weeks sub-plan and a remaining-weeks sub-plan. Furthermore, the first-12-weeks sub-plan can be considered from four different perspectives or as four sub-problems: PPLbased is for one assembly line only; time-based for one planning week; component-based for dealing with component shortage problems; and capacity-based just for capacity shortfall problems. Actions can be taken when planners try to develop alternatives. As there are different abstract levels involved in the problem space, a planner needs different types of information support for each level. 12 month plan Evaluation first 12 weeks remaining weeks Evaluation PPL-Based subproblem Time-Based subproblem Component-Based subproblem Capacity-Based subproblem Evaluation Action n Action 2 Action 1 Actions Final Evaluation Figure 1. Production Planning Problem Space There are two challenges for visualizing production planning data: how to handle massive data in both size and dimensionality, and what should be the geometric structures for the data and the relationships among the data. A typical manufacturing plant can easily have hundreds of products, thousands of components, several assembly lines, and tens or hundreds of machines or tools. It is impossible to show all data items on a computer screen at once. Although detailed data items might be needed at some point during the problemsolving process, most of the time they are not necessary. We introduce “indicators” as aggregation results for critical data objects. These indicators provide relevant information for the planners at different stages during the problem-solving process. Each of the indicators, and some of the original data objects, must have a basic geometric structure (called “abstract”) that should be consistently used for the entire problem-solving process. The geometric structures indicating relationships among indicators and data also need to be carefully designed so that they are meaningful to the planners and representable on a computer screen. The procedure of visualizing planning data for production planning support is shown in Figure 2, where only one sub- Proceedings of INFORMS First Conference on Information Systems and Technology, May, 1996 problem (one node) in the problem space is shown (first-12-weeks). The entire process of visualizing planning data involves applying the procedure in Figure 2 to each of the “nodes” in the problem space. Problem Space Original Data Indicators Abstracts PPLs first 12 weeks planning weeks demand satisfaction BOM capacity Evaluation - revenue - capacity usage - demand satisfaction - critical subproblem products a1 a2 components availability Visuals a3 satisfaction problems components inventory demand scheduled receipts commit a4 capacity availability time a5 PPLs a6 Figure 2. Visualization Model for Production Planning Support VIZ_planner, the prototype of a decision support system for production planners, has been developed based on the above visualization model. It is able to interactively construct visual representations at different abstract levels. It also allows planners to do what-if analysis for potential actions. By visualizing critical planning data, it assists a planner in identifying production planning problems, generating and evaluating alternatives for solutions, and developing superior solutions. To evaluate the effectiveness of the visualization representations for improving planners’ problem-solving performance, a lab experiment was conducted as part of the entire research methodology. Visualizing Planning Data for Decision-Making Support VIZ_planner has two basic components: a production planning management system (named NORM_planner) that creates production plans based on the MRP II process [5, 21], and an information visualizer that aggregates and then visualizes critical planning information for planners. As it is difficult to collect real production data from a manufacturing plant for software system tests and for the experimental study, a raw data generator is developed as a pre-engine of VIZ_planner to generate all raw planning data that would otherwise be collected from a plant. Data Aggregation The purpose of data aggregation is to compress the original data into representable sizes because of limited display space (for instance, a computer screen). To reduce the complexity of the research problem, we consider components and capacity constraints only. The raw data objects involved in production planning are PPLs list, products list, unique components list, common components list, bill of materials (BOM), inventory, scheduled receipts of components, demand, and PPL capacity. Some of the raw data, such as Demand, are changeable by the planners during the planning process. The production planning management system NORM_planner calculates the time-phased plan for each of the components based on the demands, bill of materials, inventory, and scheduled receipt of components. The time-phased plan has the information about the available components list and the corresponding component shortfall list. Based on the production mix and time-phased plan, NORM_planner then calculates the producible products based on component availability. Capacity information is given to each of the six assembly lines during the planning time period. The final production plan of the products (called commit) is determined by both the capacity and the components' availability. The data objects needed for the planner to evaluate the final plan include: revenue profile, demand satisfaction (by comparing demand and commit), product satisfaction for each of the products based on available components, critical component shortfall, and the information about each product supported by each of its components. All the data objects except the revenue profile incorporate many detailed data items. These detailed data items do not provide an overall understanding of the planning problem. They are what we want to aggregate into indicators. All the indicators are taken as percentages so that relative comparisons are possible. Demand Satisfaction Indicators The production demands of a plant can be measured by revenues (in dollars) or other factors. We use the ratio of achievable revenue to required revenue to indicate how many of the production demands can be satisfied based on tool capacity availability and component availability. For example, if the plant is planning to achieve $10,000 for some planning period, and only $5,890 can be achieved according to the available components and capacity, then the demand satisfaction indicator is 58.9%. Each of the six PPLs (Production Pull Lines) has a demand satisfaction indicator for each of the planning weeks, Proceedings of INFORMS First Conference on Information Systems and Technology, May, 1996 NL ∑f DLk = n• Pkn n =1 NL ∑f • 100 n• 1≤ L ≤ 6 Dkn n =1 where DLk is the demand indicator for PPL L at week k, NL the number of different products produced by PPL L, fn the profit (in dollars) of product n, Dkn the required production quantity for product n at week k, and Pkn the actual quantity of product n based on available capacity and components. Component Availability Indicators ECAT has more than 2000 different types of components. During the production planning period, demands are allocated to products, and products are allocated to PPLs. Some components are used by single types of products, some are used by multiple products. The proportion of the quantity of all available components to the total quantity of required components is the indicator for component availability: ML ∑ (R km CLk = - Skm) m =1 • 100 1≤ L ≤ 6 ML ∑R km m =1 where CLk is the component indicator for PPL L at week k, ML the number of different components after decomposing NL products produced by PPL L, Rkm the required quantity for component m at week k, and Skm the shorted quantity of component m at week k. Capacity Availability Indicators In ECAT, each assembly line has production capacity calculated in hours of tool usage. According to the production demands of that assembly line, the potential capacity utilization is the proportion of required hours to available hours. We use the utilization as the indicator for capacity availability, NL ∑D ULk = kn • Tn n =1 HLk • 60 • 100 1≤ L ≤ 6 where ULk is the utilization for PPL L at week k, NL the number of different products produced by PPL L, Dkn is the required quantity for product n at week k, Tn is the average minutes required for producing a single unit of product n, HLk is the available hours for PPL L at week k. Information Visualizing The next step is to map data and/or indicators into visual images, which provides insight into planning problems. In order to design the geometric structures for most of the data objects and indicators, we studied the cognitive processes and activities of the planners and found that most of the cognitive activities involve many comparisons. Since the final visual images should not be too complicated for business managers to understand and use, we extended the traditional bar charts and used them as our theme for the entire visualization system. Most of the values are represented by bars in a broader sense (such as areas or lines) because bars are good for comparisons [6] and are well understood by people, including planners. The layout of multiple data objects/indicators in one visual image is determined by the dependency relationships among the data objects/indicators. We say data object A is dependent on B, or B determines A (fully or partially), if A is a function of B: A = F(B). In this case we say there is a dependency relationship between A and B. In a virtual multi-dimensional space, each data object/indicator has its own axis just as in an ordinary one-dimensional space. The following rules, as partially depicted in Figure 3, apply to data objects/indicators to make them geometrically connected. Rule 1. If A is determined or partially determined by B, then A and B construct a 2D plane by sharing the same origin. For example, demand satisfaction (A) is partially determined by components availability (B). Rule 2. If A and B are time series data or location data and determine other data objects/indicators at the same time, then A and B construct a 2D plane by sharing the same origin. For example, it is meaningful to say the capacity availability (C) for assembly line 2 (B) at planning week 3 (A). Rule 3. If A and B have no dependency relationship, but they both partially determine C, then A and B could be in a parallel position sharing the same origin. For instance, component availability (A) and capacity availability (B) have no dependency relationship between them, but they both determine the demand satisfaction (C). Rule 4. All elementary graphing techniques and rules, when not conflicting with the above three rules, apply to up to 3 data objects/indicators. Rule 5. Combinations of the above rules will be used to geometrically connect all the data objects/ indicators involved in one visual image. Proceedings of INFORMS First Conference on Information Systems and Technology, May, 1996 C C A A B Rule 1 B A (Time) (Location) Rule 2 B Rule 3 Figure 3. Geometry Construction Rules From the virtual multi-dimensional space to the final 2D surface of a computer screen, typical visualization or computer graphics techniques, such as projections and perspectives, are used. Figure 4 through Figure 7 are the final visual images at different abstract levels that correspond to humans’ problem-solving stages. They illustrate the design methods and rules listed above. These visual images picture a scenario of a planning process for six assembly lines over 12 weeks, where 50 products and 812 components are considered. The color coding is used for better human perception [4, 19, 20]1. Green is reserved for demand satisfaction, orange and red for components' availability and products satisfaction, blue for capacity availability, and purple for no demand during the time period (see Products Satisfaction By PPL 5 in Figure 6). The gray background is for showing the values of bars. The color coding is consistent over all visual representations. Relationships among data objects are implied in the visual images by the ways they are laid out according to the rules. Figure 4 shows the global problems and potential at the highest abstract level. It has two visual images. The left one is the Global View for Satisfaction & Potential of the status of the planning results. The visual representation is at a global and abstract level without showing details. There are five data objects involved: twelve planning weeks, six assembly lines, component availability, capacity leftover, and demand satisfaction (which is dependent on both components and capacity availability). This visualization shows the relationships among these data objects and the change trend of each data object. It provides the planner a landscape view of the planning problem from the satisfaction and potential view. For example, demand satisfactions (the green bars) are affected by both capacity leftover (blue bars) and component availability (pink bars), while the latter two seem to have no necessary relationship between each other (parallel positions on the same plane). Among all the PPLs, PPL4 (fourth from left) has consistent capacity leftover. This implies that this PPL can handle more demand than it does now. For PPL6 at 1 Color images are available from the first author upon request. planning week 1 and week 2, the non-perfect demand satisfaction is due to the components shortage, since there is some capacity leftover for those two weeks. During the planning process, the planners want to know how severe the problem is. They want to look at the planning results from problem’s view. The visual image on the right in Figure 4 has the same layout and shows the same planning results from the shortfall aspect. In this visual image, we can see that PPLs 1 and 5 have severe capacity shortfall problems, where PPLs 2, 3, and 4 have severe component shortage problems. This image shows the unbalanced production load to the six assembly lines and implies a solution to the problem at a high level without the need to look at the detailed data items. By comparing the two visual images in Figure 4, the planner can get a very thorough understanding of the planning situation. If the planner wants to focus on a specific PPL or a specific planning week, s/he can “zoom in” from the global view to get the perspective s/he wants. In Figure 5, the planner is focusing on PPL5 by zooming it in but still considering it within the context of the whole factory. The planner is also considering planning week 4. Figure 6 has two views indicating the component shortage problem that affects productions satisfaction. The Global Products Satisfaction view shows the satisfactory situation for each product in each PPL throughout all planning weeks. For example, PPL5 has eight products (eight lines) and they all have problems in week 6; this leaves the corresponding green bar (demand satisfaction) below one hundred percent. From here the planner may want to further explore the situation of each product in this PPL, from which comes Products Satisfaction By PPL5, the right image in Figure 6. This picture lists the product identification numbers and shows the unsatisfied situation by detailed numbers. For instance, only 37% of product P_26 can be produced in week 3 due to the component shortage problem. Figure 7 gives more details for finding out what causes 37% satisfaction of P_26. Product P_26 Supported by Components lists all the ID numbers of the components required by P_26. The last three blueinked identifications are common components that are shared by multiple products. In this picture, each bar corresponds to one component for one week and indicates the satisfaction the component can provide for product P_26. Week 2 through week 8 show the component shortage problems. As the complete sets of components are needed for the production of P_26, the picture shows which component is most critical. For example, in week 3, both common components 40 and 44 are short. However, common component 44 (the Proceedings of INFORMS First Conference on Information Systems and Technology, May, 1996 shortest bar) is more critical. In other words, C0_44 determines how many of P_26 can be produced for this week. however in week 6, it is C0_40 that is more critical. C0_44 is shared by another product P-41, while C0_40 is needed by a total of four products. If the planner is concerned that sharing of common components may cause problems for P_26, or is considering changing the production mix, then s/he can view the Allocation of Common Components at Week n, where all sharing products, allocation amounts to products, and additional amounts needed are indicated. Figure 7 shows the Allocation of C0_44 at Week 3 and the Allocation of C0_40 at Week 3. Re-allocation of the available amounts of common components may be an alternative for solving or reducing a component shortage problem for some products. What-if analyses are supported so that the planner can evaluate possible alternatives or actions. Visual images are affected when the planner changes planning data. Evaluation The prototype system has been informally evaluated by real-world planners from different manufacturers. Based on the encouraging comments and suggestions from these planners, a lab experimental study was conducted to evaluate the effectiveness of the prototype system on problem-solving performance. A total of 13 graduate students who have either taken production planning courses or had real world production planning experience participated in the study. Two randomly assigned groups worked on the same decision problems by using two different computer systems respectively within a limited time period: one was a traditional MRP II type system (NORM_planner) with tabular format for data displays, and the other was VIZ_planner with added visual images. In order to pursue the experiment within affordable mental effort by the subjects, the production planning tasks (decision problems) were simplified with only components constraints, one assembly line, and limited products and components. Corresponding to this simplification, only three visual representations were used in VIZ_planner: Product Satisfaction (Figure 6), Products Supported by Components (Figure 7), and Allocation of Common Components at Weeks (Figure 7). The subjects were trained in basic production planning concepts and decision problems, and in using corresponding systems before the experiment. They were also aware of the rewards for best performance. Experimental data were collected by asking the subjects to fill out questionnaires immediately after the experiment, and by computer logs. The results of the experiment indicate that (1) the Viz group generated more alternatives for solutions than the NORM group did; (2) the Viz group made more efficient changes in the raw data in order to achieve high revenues than the Norm group did; (3) the Viz group was more confident about the decision tasks than the Norm group was; and (4) the Viz group was more satisfied with the outcomes than the Norm group was. There was no difference found in the quality of the solutions and perceived information overload, which may be due to the reduced complexity of the decision problems that decreases the advantages which VIZ_planner has in dealing with multiple constraints and huge data volume. All the Viz users felt that the visualization system was cooperative with their problem-solving strategies, while only half of the Norm users felt that NORM_planner was cooperative with their problem-solving strategies. Another interesting finding from the experiment is that the Viz group had only 15 minutes to watch a demonstration of VIZ_planner, and 40 minutes for practice in getting familiar with it after they knew how to use NORM_planner. This means that the final visual representations for manufacturing production planning are very easy to understand and use. Also, 83.3% of Viz members had intensive use of the visual representations during their problem-solving process. One subject who did not use visual representations much explained that “I prefer to use exact data rather than percent information.” The same subject, when asked why he selected Allocation of Common Components at Weeks (Figure 7) as his most-liked visual, said “because it gives additional information that I cannot get easily from the real figures.” Conclusion In this paper, we described the research results of developing multi-dimensional interactive visual representations of management data that are huge in volume, have complicated relationships among data, have no physical objects corresponding to them, and have to be quickly understood and interpreted so that effective interactions and decision-making can be carried out by high-level managers. A visualization system for manufacturing production planning decisionmaking support has been designed and implemented in Sun Workstations based on the proposed visualization model. A preliminary evaluation in a lab experiment has shown that the visualization system can help a planner to develop more alternatives for solutions, make more efficient changes on the raw data, and feel more confident about the tasks and more satisfied with the outcomes. The evaluation has further supported the Proceedings of INFORMS First Conference on Information Systems and Technology, May, 1996 advantages of the user-centered manufacturing production planning visualization model. As visualization of large data sets is a problem of concern in many business domains and yet little research has achieved any results in applying visualization to business domains, this research has both theoretical and practical values. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. Ahmadi, Javad H., Peng Si Ow, Chae H. An, SORCERER: Production Source Allocation System, Manufacturing Productivity ITL, 1992. 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