# A Survey of the Literature on Order-Picking Systems by Combining Planning Problems
## 6 Results  
Considering the assumptions made in the introduction and according to the information obtained from Tables 3, 4 and 6, the review process of articles from 2010 to 2021 in the present study showed the researchers' attention to reducing operating costs by focusing on order selection activities such as routing, batching, and space storage. In Figure 3, it is also \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Articles** & **Solution Methods** & **Assignment** & **Routing** & **Batching** & **Sequencing** & **Tardiness** \\ \hline [PERSON] et al. [50], [PERSON] et al. [22], [PERSON] et al. [30], [PERSON] et al. [43] & ACO & ✓ & ✓ & ✓ & ✓ & \\ [PERSON] \& [PERSON] [85], [PERSON] et al. [90], [PERSON] et al. [36], [PERSON] \& [PERSON] [93], [PERSON] et al. [25], [PERSON] \& [PERSON] [64], [PERSON] et al. [13], [PERSON] et al. [22], [PERSON] et al. [18] & GA & ✓ & ✓ & ✓ & ✓ & ✓ \\ [PERSON] et al. [18], [PERSON] et al. [30], [PERSON] et al. [71], [PERSON] et al. [42] & PSO & ✓ & ✓ & ✓ & ✓ & \\ [PERSON] et al. [31], [PERSON] [53], [PERSON] et al. [5], [PERSON] \& [PERSON] [33] & TS & ✓ & ✓ & ✓ & \\ [PERSON] et al. [12], [PERSON] et al. [46] & PSA-ACO & ✓ & ✓ & ✓ & ✓ & ✓ \\ [PERSON] et al. [45] & As-algorithm & ✓ & ✓ & ✓ & ✓ & \\ [PERSON] \& [PERSON] [64], [PERSON] et al. [43], [PERSON] et al. [66] & integer programming & ✓ & ✓ & ✓ & \\ [PERSON] et al. [19] & exact method & ✓ & ✓ & ✓ & ✓ & \\ [PERSON] et al. [46] & CG & ✓ & ✓ & ✓ & ✓ & ✓ \\ [PERSON] \& [PERSON] [74], [PERSON] [35], [PERSON] et al. [49], [PERSON] et al. [39], [PERSON] \& [PERSON] [47], [PERSON] et al. [21], [PERSON] [37], [PERSON] et al. [7] & Heuristic & ✓ & ✓ & ✓ & ✓ \\ [PERSON] et al. [5], [PERSON] et al. [61], [PERSON] [14], [PERSON] et al. [67], [PERSON] et al. [20], [PERSON] et al. [38], [PERSON] \& [PERSON] [23] & VNS & ✓ & ✓ & ✓ & ✓ & ✓ \\ [PERSON] et al. [87] & [PERSON] & & ✓ & ✓ & ✓ & \\ [PERSON] et al. [8], [PERSON] \& [PERSON] [82] & [PERSON]\&[PERSON] & ✓ & ✓ & \\ [PERSON] \& [PERSON] [33] & Hill climbing & & ✓ & ✓ & \\ [PERSON] et al. [84], [PERSON] \& [PERSON] [40], [PERSON] et al. [62], [PERSON] et al. [63], [PERSON] et al. [88], [PERSON] et al. [96], [PERSON] \& [PERSON] [83] & [PERSON] \& [PERSON] [34], & Simulation & ✓ & ✓ & ✓ & \\ [PERSON] \& [PERSON] [44], [PERSON] et al. [91], [PERSON] et al. [52], [PERSON] et al. [29], [PERSON] et al. [69], [PERSON] \& [PERSON] [17], [PERSON] \& [PERSON] [16] & [PERSON] & ✓ & ✓ & \\ [PERSON] \& [PERSON] [55], [PERSON] et al. [1], [PERSON] et al. [78], [PERSON] et al. [7], [PERSON] et al. [6], [PERSON] et al. [65], [PERSON] et al. [54], [PERSON] \& [PERSON] [51] & Analytical models & ✓ & ✓ & ✓ & \\ [PERSON] \& [PERSON] [86], [PERSON] \& [PERSON] [76], [PERSON] & [PERSON] et al. [70], [PERSON] et al. [4], [PERSON] et al. [5], [PERSON] et al. [72], [PERSON] et al. [24], [PERSON] \& [PERSON] [60], [PERSON] [95], [PERSON] [79], [PERSON] \& [PERSON] [41], [PERSON] \& [PERSON] [92], [PERSON] \& [PERSON] [94], [PERSON] \& [PERSON] [88] & Other & ✓ & ✓ & ✓ & ✓ & ✓ \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Studies using mathematical programming methods. evident that the studies conducted in the field of OPS from 2010 to 2021 have had a similar course, showing that OPS issues are still of interest to researchers. Although most studies initially focused on routing and batching problems, researchers' attention, in recent years, has been directed to simultaneously combining problems and considering issues such as latency and makespan. The results of this review study revealed the importance of integrating the problems related to multi-objective picking planning to effective management of order-picking operations. The results indicated that the time horizon of decisions could significantly affect the proper approach to solving the hybrid planning problems. On the one hand, issues can be combined by analyzing the interactions between predetermined policies specific to each planning problem. On the other hand, two or more planning problems can be integrated and solved.