Hierarchical decision levels

One approach reUes heavily on heuristics but allows the engineer to interact during the synthesis procedure through a framework of hierarchical decision levels (58,59). 

Hierarchical Decision Levels for Process Synthesis (Douglas, 1992)... 

To develop and demonstrate the benefits of SC models that allow integrating different business functionalities and hierarchical decision levels. 

Frameworks that reduce the computational complexity of scheduling problems are crucial for the eventual integration of the SC hierarchical decision levels. As mentioned before, that integration permits to find more realistic and feasible solutions for the SC design and planning. What is more, its consideration may improve the resolution of SC incidences and SC visibility. These topics will be further discussed in Chap. 9. 

Notice that for the actual period the proposed algorithm is considering the detailed scheduling, therefore disturbances can be contemplated as frequent as the time bucket utilized in the scheduling formulation. It is also important to point out that we are integrating the three standard hierarchical decision levels however, more decision levels may exist in an organization. In that case, the disturbances can be considered as frequent as the time bucket of the lower decision level in case of using discrete time SC formulations. Continuous time formulations should overcome this drawback. 

A hierarchical design procedure for process synthesis can be used in conjunction with a flow-sheeting program to analyze, evaluate, and optimize the options (60). The emphasis is on starting with the simplest possible models that will give answers to a particular question quickly so that the questions to be asked at the next decision level can be formulated. At each stage, it is necessary to ensure that the level of detail in the model is sufficient to give rehable information. 

The top-down approach, which defines appropriate hierarchical coordination mechanisms between the different decision levels and decision structures at each level. These structures force constraints on lower operating levels and require heuristic decision rules for each task. Although this approach reduces the size and complexity of scheduling problems, it potentially introduces coordination problems. 

Advanced planiung systems. Integrated enterprise-level planning systems supporting hierarchical decision-making. 

Puigjaner and co-workers in Chapter D2 explore the interactions between the various decisions levels linked to the batch control system. The work is motivated by the increasing shift in chemical industry to higher added value products that are usually produced batch-wise (Ref 1). Optimal design, analysis, and scheduling of batch processes lead to hierarchical and interconnected decision levels that require a holistic approach. A comprehensive overview of the requirements and standards for automatic batch control systems provides the basis for the... 

For a plant design problem, students will need guidance on the hierarchical levels of decision making to choose a process. Also checklists of information needed for the design of typical parts of commercial processes prove invaluable. These are provided in Dr. Long s student handout. 

Heuristic based approaches are more relevant for structured products. The most well known heuristic based approach is the hierarchical decomposition method developed by Douglas (Douglas, 1988). In the first level of this method one only looks at the input-output structure of the process. In subsequent levels more detail is added, finally ending with the entire flowsheet. Design decisions are made by using heuristics and short-cut models. An alternative method is due to Siirola (1996) means end analysis. In this method the properties of the feedstock and the desired products are compared. Tasks are defined to eliminate the property differences between the feedstock and the desired product. 

The structure tends to be hierarchical, although this hierarchy does not resemble a traditional decision tree. Each branch point may have any number of branches. The decision about which branch to take at each level can be viewed as an independent expert system. 

The first step in using the AHP to analyze a decision problem is to hierarchically break down the decision problem (objective) into its constituent components and identify the alternatives to be evaluated. The resulting hierarchy consists of the overall objective (goal) and one or more levels of sub-objectives. The alternatives to be evaluated are added at the lowest level of the hierarchy. According to Saaty (1980, pp. 79-83) a cluster should not contain more than 7 elements because results from psychological tests show that 1+1-2 are the maximum number of elements a person can effectively compare simultaneously. 

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