# The Future of Factories: Different Trends
###### Abstract
Data originated from the activities of PLM mainly focuses on physical products rather than virtual models. The lack of convergence between physical products and virtual models gets data in the product lifecycle isolated, fragmented, and stagnant, which is useless for manufacturing enterprises [2]. In this scenario, Cyber-Physical Systems (CPS) have the central role of enabling a digital twin model. One of the key aspects of the digital twin model is establishing a link between physical products and virtual models. The digital twin model enables the designer to test, predict, and verify product performance by simulating a design scheme and manufacturing process before diving into the production process. A general definition of the Digital Twin model is given by [5] as: \"Digital twin model is an integrated multi-physics, multi-scale, probabilistic simulation of a complex product and uses the best available physical models, sensor updates, to mirror the life of its corresponding twin\". To this end, the digital twin model consists of three parts. A physical part where products and manufacturing assets compose the existing shop floor layer. A virtual part where virtual models of products and manufacturing assets enable constructing a virtual model to test, simulate, and verify product performances. The last part is a link between the physical layer and the virtual layer to synchronize and integrate the physical and the virtual world. To address this new shortcoming, a paradigm shift is needed to build the next generation of Factory of the Future. The digital-twin-driven manufacturing process enables industries to face new challenges arisen from the change of market requirements. For example, the new emerging trend known as product mass customization puts final customers at the center of the manufacturing process by allowing mass customization of products. The driven digital-twin manufacturing process fits these requirements by allowing industries to rapidly change manufacturing processes or customize them according to customer requirements. The implementation of the digital twin model is addressed at different layers of the supply chain. The main contribution of this review paper is to report about the investigation of the state-of-the-art w.r.t. paradigms, frameworks, and tools to realize the digital twin model in the two considered programs, i.e., Industry 4.0 and China 2025. In this sense, different literature trends identify new paradigms for the realization of the factory of the future. The paradigm _Virtual Factory_ (VF) has been used primarily referring to European factories, _Digital Factories_ (DF) and _Smart Factories_ (SF) paradigms having a widespread in European and China, and _Cloud Manufacturing_ (Cmfg) known as a new paradigm for the digitalization of Chinese industries taking its advantage from the cloud computingparadigm. In our study, we point out the common aspects of the approaches as well as the differences among them, comparing in particular Cloud Manufacturing and Virtual Factories. As a final contribution of our study, we envision the building blocks of the factories of the future comprising multiple technologies at a different scale. In particular, we analyzed core technologies which promote the digitalization of the supply chain, as well as some interoperability issues to address while enabling inter-factories cooperation. The paper is organized as follows. We introduce in Section 2 the methodology adopted in this research to extract relevant papers in the field. Then, we introduce the characteristics of _Digital Factories_, discussing their extensibility as Smart and Virtual Factories (Section 3), then we describe the _Cloud Manufacturing_, providing an example of its application (Section 4). Starting from the above descriptions, we propose in Section 5 a comparison between Virtual Factory and Cloud Manufacturing, while Section 6 highlights the main architectural components for the enablement of a factory of the future, starting from the paradigms examined in the previous sections.