ERP system

These are software packages that can be configured according to users needs, e.g. enterprise resource planning (ERP) systems. Full life cycle validation is required. 

PP/DS focuses on determining an optimal production sequence on key resources. In PP/DS, a more detailed modeling than on the SNP planning level is chosen. This does not mean that all products and resources within a real-world production process need to be considered for PP/DS planning as nonplanning relevant products and resources can be excluded from the integration process between the ERP system and the planning system. 

The other master data elements for which an integration process is required are recipes. Recipes used within the PP/DS module are tightly integrated with the recipes in the ERP system. For complexity reduction in master planning, as outlined in the SNP section above, simplified recipes are used in SNP. These are derived from the PP/DS recipes by a flexible, automated conversion process. 

In the independence approach the planning functions are stripped from the old-fashioned ERP system and a modem complete APS system is added as a separate server system with an independent persistent data model and integrated by an interface (Fig. 12.2). Some users of the ERP system also use this separate APS system. This approach is supported, e.g., by the software products SAP APO resp. 

In the embedding approach the ERP system is enhanced with subordinate planning systems that are integrated into the user interface of the ERP system and create a local temporary data storage (LiveCache). All data is still held persistently only in the ERP system (Fig. 12.3). This allows for the LiveCache to use a projection of the ERP data model that is more suitable for APS purposes. This approach is used, e.g., by the software product OR Soft SCHEDULE++. 

The embedding approach may require an improvement of modeling in the ERP system (i.e., to maintain additional detailed information for APS purposes) but it can utilize all established business processes, data models and infrastructures. Introduction of the subordinate planning system can be done step-by-step with minimum impact on established business processes. Integration is fully guaranteed... 

For the planning of a multipurpose plant one has to map the structure of a master recipe to the detailed device structure of the plant with regard to a given time in the future. This process can be done automatically, e.g., with the SAP ERP system where it is called convert. The result is a process order as a concretization of a master recipe. A process order tells the production operator at which time and on which device a given batch production step has to be executed. This simple conversion can result in a situation where a selected device is already allocated to a different process order at the given time, thus the production plan may not be feasible. 

The big players in the chemical industry have developed very powerful company-specific ERP systems (enterprise resource planning earlier this type of system was denoted as production planning and control) since the 1960s. The growing costs to maintain and adapt these systems have motivated the move to integrated standard business software systems in the last decade. The majority of the big chemical companies use SAP R/3 resp. SAP ERP from SAP AG other well-known solution vendors include Marcam (now part of Infor) and JD Edwards (now part of PeopleSoft resp. Oracle). 

To integrate an organizational unit that uses multipurpose batch plants into the company, IT infrastructure with its ERP system, a hierarchical planning approach is most often used. Starting from a material requirements planning (MRP) run, capacity requirements are determined and roughly checked, although the check of the capacity requirements is not directly combined with the material requirements. 

Planned orders and other information are sent from the ERP system to a scheduling system via an interface. The scheduling system has its own database and a number of different automatic and interactive scheduling functions. Scheduling results are sent back to the superior system via an interface at the end of the scheduling process. This loose integration respects the hierarchical concept and the autonomy of the planners. 

The APS system is supported by an independent modem data model that is often based on generic input/output nodes and their dynamic combination in complex networks and thus better suited for algorithmic processing and optimization than the transaction-oriented business data model of the ERP system. 

Due to the fact that one might not want to use all ERP business data objects in the APS system, an integration model is used to define for which plants, resources, materials, customers, etc., the integration interface should be active. The APS system also allows to maintain additional master data or to modify and enhance master data that came from the ERP system. Sometimes there are also additional types of master data (e.g. resource setup matrix) or information fields to master data (e.g., scheduling horizon) that really have no analogy in the ERP system and thus have to be maintained directly in the APS system. 

The consequence is that data has to be maintained and consolidated in two systems. Because also some planning and production execution functions will stay in the ERP system, there is quite often the need for the planner to work with both systems and to gather information from both systems (e.g., customer order details, confirmations from production execution, which is handled in the ERP system) to make planning decisions. 

A representative for this approach is the product APO resp. SAP SCM of SAP AG that is most often used in conjunction with the ERP system SAP R/3 resp. SAP ERP. 

Quite often not all modeling capabilities of an ERP system are used to their full extent. For instance it is possible to model continuous material flow, alternative devices, campaigns, resource nets, operation relationships, etc., in the ERP system, thus there is no need for an enhanced model in the scheduling system. The ERP system however lacks the proper algorithms to use the enhanced data (e.g., for detailed scheduling instead of rough capacity leveling). 

Thus the alternative approach is to create enhancements (add-ons) to an ERP system that do not have their own persistent database and provide additional interactive functions, visualization and algorithmic processing of enhanced model data. The add-ons create a temporary local data storage (LiveCache) to effectively process the enhanced data. However, all data is stored persistently exclusively in the ERP system. This allows for the local LiveCache to use a mapping of the ERP data model that is structured in a way that is more suitable for APS purposes. Additionally the... 

Production planning/optimization always requires a compromise to be found by the humans in charge of decision-making. In the process of finding this compromise, one needs scheduling programs that are integrated into the ERP systems. 

Throughout the data collection phase unexpected complications were encountered in the pilot application because calculations obtained from the ERP system were often not comparable across plants. Even if the same ERP system was used (which was not the case for all sites considered), different conventions were used for distributing costs across products. Additionally, recipes pulled from the ERP system often did not reflect the actual recipes employed in production. For example, significant differences in absolute raw material quantities required and relative relationship between the different raw materials were found. As similar problems are also reported in the literature discussing practical applications of mathematical modeling approaches (e.g., Kallrath 2000, p. 817 Lee and Billington 1995, p. 46), this appears to be the norm rather than a company-specific exception. 

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