• Hierarchical production planning decomposes complex manufacturing systems into aggregate and detailed levels, enabling rolling-horizon planning, disaggregation, and cross-level objective alignment [4], [9], [15], [19].

• Lot sizing in multi-level and multi-stage settings integrates capacity and lead-time considerations, blending analytical formulations with heuristics to reduce costs and improve responsiveness [8], [7], [2], [12].

• Flexible Manufacturing Systems research emphasizes modeling, control policies, and performance evaluation under computer-controlled environments, including nonlinear integer formulations and loading strategies [1], [3], [13].

• Scheduling across multi-stage, multi-item networks with capacity constraints is explored via network programming and policy studies to identify bottlenecks and improve throughput [20], [11], [18].

• MRP/GT integration and education frameworks explore translating group technology concepts to MRP and planning horizons, guiding production planning practice [6], [19].