## 4 Case study
### Modeling of Workshop Entities by Q-Holons and Their Assignment to the Three Levels of the QHAR  
A Q-Holon allows us to represent not only the characteristics of an entity (or an actor), but also the flows that it can exchange with the other entities. The Q-Holon's characteristics are described by the attributes/properties of the Q-Holons four dimensions (physical, cyber, human, and energy) and the eventual operations that it can perform. With regard to flows, they can be of three types: energy, material, and data/information. The workshop manager, assisted by an ERP system, plays the role of the centralized controller. This role is modeled by the Q-Holon \"Centralized controller\". This same workshop manager is assisted by an MES to perform the \"Decentralized controller\" role; they are also represented by a Q-Holon. The machining center, conveyors 1 and 2, the drilling station, the assembly station, and the AGV are modeled by a Q-Holon each, all belonging to the Execution level. We could have integrated the operator-drivers of the different workstations into the Q-Holons that represent these stations. However, as the operators could carry out other tasks in addition to the driving of workstations, we decided to model them by autonomous Q-Holons. The public energy distribution network is also modeled by a Q-Holon. We recommend the use of two types of SysML diagrams to represent all aspects of a Q-Holon-based model: a BDD diagram and an IBD diagram. The BDD diagram, as shown in Figure 8, represents the attributes/properties and operations of the Q-Holons, while the flows exchanged between the Q-Holons are described by the IBD diagram (see Figure 9). Figure 10 shows an example of the flows exchanged between two entities of the Execution Level; namely, the Assembly center block. This block is constituted by a cobot associated with an operator, each of which is characterized by the required spatial attribute which represents the safety space necessary to avoid collisions between the two entities. Both the cobot and operator receive information from the local control center (i.e., production rules and operational orders), as well as the parts that need to be assembled. The energy used here can be supplied by the public energy network or locally produced by the cobot, if possible; this is modeled by the in/out (in and out) energy ports. Additionally, the cobot exchanges information with the operator through a human-machine interface. As output, assembled products are transferred and real-time reports, operational responses, and cobot- and operator-specific data are sent to the local control center. Figure 7: Manufacturing workshop taken as a case study. Figure 8: Attributes/properties and operations of Q-holons modeling entities of workshop. The aim of this case study was to test and verify the ability of the proposed architecture to allow self-reconfiguration. For this purpose, the case study had to be representative of existing production workshops. This representativeness must be verified, in terms of the entities that make it up as well as the operations carried out. Thus, there are classic  
Figure 10: Assembly center IBD diagram. Figure 9: IBD Diagram. entities, such as CNC machines and drilling machines, as well as more recent equipment, such as AGVs and cobots. In terms of operations, machining, assembly, and transport operations are carried out. Care has also been taken to simplify the case, to make it easier to understand without impacting its representativeness. Through this case study, we can see that the Q-Holon concept, thanks to its four dimensions and three types of flows, makes it possible to model the entities/actors of the production system and potentially allows for automatic or semiautomatic reconfiguration. Indeed, thanks to the use of Q-Holons, each entity/actor is represented by its attributes/properties, its operations, and the flows it can exchange with the other entities/actors.