## 3 A Decision Support System for Detailed Scheduling
### DSS Functionality for the Scheduling Process  
Due to the complexity of its production planning process and a deficient IT infrastructure, the studied company has encountered a slew of issues over the last few years, including missed deadlines, accumulated late orders, supernumerary production orders, excessive component inventory, poor outsourcing management, lax releasing policies, non-systematic dispatching methods, insufficient workload control, and low shop floor visibility. The detailed production scheduling system visualizes production groups over a planning period (week), transfers dispatching control from foremen to planners, and equips the latter with all the decision-support tools necessary for releasing, dispatching, workload control, and dynamic event management. While this is by no means a panacea, it does assist the planner in better organizing and controlling the whole manufacturing process by adding another level to the hierarchical planning framework, one that goes beyond a day or shift to a single period (week). One of the main changes in the production process was the shift of order release from the PPC to the new application by creating the production order backlog. From then on, full control is relinquished to the DSS and the planner. Through manual selection, the planner releases orders of a single functional group from the backlog while concurrently checking the current shop floor workload. The released orders are fed to the two-level dispatching modules that perform raw (first level) and fine-tuned (second level) dispatching. As will be later demonstrated, these modules utilize priority dispatching rules (PDRs), and as such, are myopic in their approach and do not by any means optimize the end schedule. However, due to their striking speed (scheduling takes a maximum of 6 s even for the assembly group), they were preferred. The schedule created is depicted in a Gantt chart and is the GUI; the planner will be used to perform the remaining functions. Once dispatching is performed, the planner proceeds to alleviate bottlenecks through the manual transferring of orders (e.g., to later planning periods or alternate work centers). At the same time, the planner receives feedback from the G-DSS regarding the load of the bottleneck and the alternate centers and the impact his decision may have. Order preemption may also be performed to conclude a specific order quantity within the current planning period and the remaining whenever the planner (or the preemption algorithm) sees fit. All precedence constraints between production orders are not considered to that point of the production process due to the extremely complex BOM structures. Therefore, the following technique is employed: The G-DSS focuses on a single functional group at a time and identifies one-level child-father pairings within the same planning period while regarding their proper orientation as a soft constraint. When the BOM precedence constraint satisfaction module is triggered, a hybrid TS/VNS algorithm runs according to the pseudocode presented later in the paper. The algorithm's output is the proper orientation of as many child-fatherpairings as possible. Due to the make-to-stock policies, the SME employs the remaining pairs, which, although wrongly oriented, may still belong to a feasible schedule. Child stock may be utilized to commence production of a father whose potential starting time is earlier than that of his child. To fully evaluate the feasibility of the disoriented pairs, the run of the TS/VNS algorithm is followed by the available-to-manufacture (ATM) algorithm that mimics the available-to-promise (ATP) module of APS systems by regarding the father as the customer who wishes to procure parts from a supplier that is the child. More details on ATM and its relevant pseudocode will be given later.