## 2 Literature Review
### Dynamic Scheduling in Production Systems
#### 2.1.3 Predictive-Reactive Rescheduling
**Robustness:** This criterion is defined as the deviation in the performance of the actual schedule from the initial schedule. This measure indicates the closeness of the actual schedule's performance to the initial schedule. In fact, robustness is associated with the changes produced in the objective function following perturbations. If the performance of a schedule is not too poor and lacking when dealing with interruptions, it is called a robust schedule. **Stability:** This criterion is the difference between the completion times of the jobs in the initial schedule and the actual schedule. When a disruption occurs in the system, the actual order may change, resulting in the cost of reallocating tools and equipment, the cost of re-ordering raw materials, etc. However, when the actual order is closer to the initial order, these costs are reduced and stability increases. Therefore, the stability criterion is about the difference between the initial schedule and the actual schedule, not about their performance. If a sequence does not change much compared to the first when faced with failures or disruptions, it is called a stable schedule. The objective function or effectiveness was evaluated in six ways in the reviewed articles. These are cost [2; 33; 34; 2], makespan [6; 16; 38; 56], Total Weighted Delay and/or earliness [29; 30; 32; 46], Total Weighted Waiting Time [26; 32], Average Stability [41], Material/Machine Usage [51; 57]. Stability has been examined in three basic ways. Deviation in the start time of each job [30; 36; 48; 58], deviation in the Total Weighted Completion Time [55], and deviation in the completion time of each job [4; 33; 39]. These are the evaluation criteria that find their place in the literature. Robustness did not find much space in the articles examined. There are studies that evaluate the completion time difference between the first and the last schedule [6; 52], performance loss [30], and the combination of efficiency and stability [36] as robustness. The concept of \"nervousness\" is mentioned as a definition in the literature [7] but as far as we know has not been expressed numerically. Scheduling nervousness was first defined as \"significant changes in MRP (material requirements planning) plans\" or \"instability\". Nervousness is the opposite of schedule stability because there is constant change in the schedule (frequent rescheduling). A \"nervous system\" offers little predictability. A rescheduling policy that provides fewer revisions increases schedule stability (and reduces schedule nervousness). In this study, we considered the change in the start time of the jobs as the stability criterion. As a robustness criterion, unlike other studies in the literature, we examined the changes in delay times. Since it is certain that the work will be delayed in our problem, our performance criterion should be the completion of the work with the least delay difference. We calculated robustness, robustness2, and robustness3 as the largest difference in the change in the amount of delay, the difference in the total amount of delay, and the difference in the total weighted amount of delay. As for nervousness, although it is mentioned verbally in the literature, as far as we know, there is no numerical example. One of the things that will increase the tension the most in a production line is production on a different machine than the planned machine. If the machine job match is changed by rescheduling while all preparations have been made according to plan, the tension of the production line increases. These preparations can be exemplified as meetings of designers, technicians, and other stakeholders; machine preparations; and consumable planning. In other words, the tension would increase if a different machine than the one determined during the initial scheduling conducted the planned work. For this reason, the differences between the initially planned and the actual machine-job assignments are referred to as scheduling nervousness.