# Digital Twins, Virtual Devices, and Augmentations for Self-Organising Cyber-Physical Collectives +
## 6 Conclusions and Future Work  
In this manuscript, we present a conceptual and modelling framework supporting the modular abstraction and design of self-organising Cyber-Physical Systems. The idea is to use multiple notions of logical devices, based on two typical constructs found in the literature--virtual devices and digital twins, which we distinguish on the basis of an identity relationship between logical and physical devices--and the adoption of a collective viewpoint. Indeed, the novel concept of the _collective digital twin_ is introduced, referring to a collection of digital twins that can be considered as a whole. This notion can further be augmented with virtual devices in order to define a richer logical system, which we call an _augmented collective digital twin_, which can be exploited to provide an augmented reality to a collection of actual, physical twins. Additionally, we perform experiments to prove that this is not just an abstraction exercise, but an enabler mechanism to improve and steer certain kinds of self-organisation processes.  
Arguably, the ideas presented in this paper can pave the path for more research and investigations.  
* _Logical abstractions for engineering of self-organising Cyber-Physical Systems_. This work discusses how purely virtual devices can be used to steer existing self-organising applications. We believe that defining logical constructs and formalising the relationship between these and physical counterparts can provide benefits for the engineering of Cyber-Physical Systems. In particular, collective-level notions such as CDTs (and strategies for implementing the corresponding digital threads) are still to be explored in depth.
* _Self-adaptive deployment of digital thread components_. The location of the software components responsible for implementing the digital thread can be optimised w.r.t. non-functional metrics such as bandwidth and energy usage. Moreover, for highly dynamic systems subject to changes affecting connectivity and available computing infrastructure, (re-)deployment decisions may be taken at runtime.
* _Self-adaptive and opportunistic management of virtual devices_. In the case study of Section 5, the system can dynamically spawn virtual nodes in order to support connectivity and self-organised exploration in a dynamic environment. In general, the trade-off between the functional benefit (current and future) and the virtualisation overhead can be analysed in order to take the best decisions for the situation at hand. This could be supported by an autonomic platform where opportunities for virtualisation, execution cost, and user preferences are altogether considered for the efficient spawning or removal of virtual devices in the system. This could be seen as a form of self-improving integration [15] of virtual and physical devices.  
Conceptualization, R.C. and M.V.; data curation, D.P.; formal analysis, D.P.; funding acquisition, M.V.; investigation, R.C. and D.P.; methodology, R.C. and D.P.; project administration, R.C.; resources, M.V.; software, D.P.; supervision, D.W.; validation, R.C. and D.P.; visualization, R.C. and D.P.; writing--original draft, R.C. and D.P.; writing--review and editing, R.C., D.P., D.W. and M.V. All authors have read and agreed to the published version of the manuscript. This work has been supported by the MIUR PRIN Project N. 2017 KRC/KT \"Fluidware\". Data Availability Statement: Data can be found at the following public archived repository: [[https://zenodo.org/record/5809103](https://zenodo.org/record/5809103)]([https://zenodo.org/record/5809103](https://zenodo.org/record/5809103)), accessed on 29 December 2021. The authors declare no conflict of interest.