## 3 The Q-Holonic-Based ARchitecture (QHAR)
### General Overview of the Q-Holonic-Based ARchitecture (QHAR)
#### 3.1.3 Execution Level  
This is the operating system, constituted by all the entities involved in the activities of the production process. These activities can be transformation activities (e.g., material removal, machining, chemical processes, deformation), assembly (e.g., welding, riveting), surface treatment, transport, control, storage, and so on. In addition to these activities, these entities also integrate certain control functions (e.g., emergency stop, alarm). The entities corresponding to raw materials and final products also operate in this level.  
The QHAR also considers the other players in the value chain, including customers, suppliers, and subcontractors.  
To explain the operating principle of the QHAR, we consider, for simplicity, a production system that receives a raw material and performs a number of operations on it to obtain a finished product.  
The centralized controller establishes a Master Production Schedule, which is a list of products to be manufactured with information on the quantities and the desired delivery date (see Table 2). The centralized controller also determines the raw materials needed to realize the Master Production Schedule and assigns, to each raw material, the Production Routing to obtain the finished product. This Production Routing (see Table 2) lists, in chronological order, all of the operations that a raw material must undergo. For each operation, it indicates the resource in charge of carrying it out and whether it authorizes this one to transfer this operation to another resource in the case of necessity (e.g., due to failure, risk of delay in view of the other tasks to be carried out, capacity). When the transfer of a task is authorized, a list of alternative authorized resources is indicated. The ProductionRouting is assigned to the corresponding raw material. The further steps are orchestrated by the raw material. Note that, here, we consider that the raw materials are intelligent; for example, raw materials equipped with RFID (Radio-Frequency IDentification).  
The raw material solicits the resources indicated for each of the operations in its Production Routing in chronological order. When a resource performs an operation, the status of the task is updated and the resource indicated for the next operation is requested, and so on until the final operation. As shown in Figure 3, if the resource that is indicated to perform an operation is not available, another resource--indicated in the \"Alternative resources\"--is requested. In all cases, whether operations are realized or not, a report is sent to the centralized controller. Negotiation and coordination between the executing entities can take place directly or through local controllers.  
The QHAR is an oligarchical architecture. Indeed, the centralized controller ensures the overall performance of the system (hierarchical control). Local controllers and con  
\begin{table}
\begin{tabular}{c c c} \hline \multicolumn{3}{c}{(a)} \\ \hline \multicolumn{3}{c}{**Master Production Schedule**} \\ \hline
**Product** & **Quantity to Produce** & **Delivery Date** \\ \hline Product 1 & Q1 & D1 \\ \hline Product 2 & Q2 & D2 \\ \hline \(\ldots\) & \(\ldots\) & \(\ldots\) \\ \hline Product n & Qn & Dn \\ \hline \multicolumn{3}{c}{(b)} \\ \hline \multicolumn{3}{c}{**Production Routing**} \\ \hline
**NO** & **Operation** & **Resource** & **Total Time** & **Due Date** & **Alternative Resources** \\ \hline \end{tabular}
\end{table}
Table 2: (a) Master Production Schedule and (b) Production Routing template.  
Figure 3: Operating principle of QHAR.  
trollers integrated in the execution level entities ensure local optimization and foster reactivity to hazards (heterarchical control).