# Digital Systems in Smart City and Infrastructure: Digital as a Service
## 1 Introduction  
Digitalization has enabled infrastructure to become smarter. The optimum use of physical space and energy, the proactive management of users, assets and processes, the efficient operation of businesses and companies have gradually benefited from the digitalization process. Countries that have introduced digitization not only in the manufacturing sector such as the use of Robotics or Internet of Things (IoT), but also in wider Smart Cities solutions, including e-healthcare or Smart Grids, have benefited from an increment of gross domestic product (GDP) [1] due to the reduction of the final Operational Cost (OPEX). The main challenge to implement a Smart City is its definition and scope; the concept of Smart City varies between pure electronic solutions integrated into the Smart city Information and Communications Technology (ICT) infrastructure such as IoT, the cloud or mobile phones and Big Data with Analytics that measures in real time its status usage that allows higher level decisions. In addition, Smart City can be implemented as frameworks and processes as government collaborative multidisciplinary environments that empower its citizens. The ICT component of the Smart City generates technical challenges based on the interoperability of the different enabling technologies, communication transmission protocols and architecture developed by independent manufactures. The key service enabled by technology for the energy resources of a Smart City is applied on its electrical distribution or Smart Grids [2], based on its three drivers Decarbonization, Digitalization andDecentralization [3]. The efficient monitoring and management of electricity through its entire process, generation, transmission, distribution and storage will enable Smart Cities and Infrastructure to meet their variable and increasing power demands in carbon free environments that protects its citizens and users against CO2 emissions. Smart Cities are also represented as large scale combination of networks with interdependent interactions [4]; the Smart City model can be defined, analyzed and optimized in order to make it sustainable. The digital twin will not be only based on a Building Information Modeling (BIM) resembling the physical infrastructure; Smart City models will converge and merge into the artificial city: the Internet and the Web. Smart cities must have drivers in order to be effective; success can be measured as increment of the quality of life of its citizens while providing a return of investment. Those drivers shall include a broad range of areas of expertise: applied social sciences, engineering, Earth sciences, and human sciences [5]. Project management applied to Smart Cities sets up stakeholder requirements via an independent and temporal delivery organization that supervises the design, construction, handover and operations [6]. The delivery organization shall produce fit-for-purpose and high quality deliverables with connections to the digital platform on Time, Budget and Scope, following the triangle of project management. The Forth Industrial Revolution [7] started with the introduction of Digitalization in the IoT, the Cloud, Blockchain, Virtualization, Robotics and Driverless vehicles that have replaced humans in routine actions, increased productivity and reduced cost. The Fifth Industrial revolution will be founded on Artificial Intelligence and Deep Learning that will entirely replace humans by taking production and management decisions. This paper presents the concept of Digital as a Service (DaaS) where any complete digitalization can be implemented independently of its associated physical infrastructure; DaaS would enable an interoperable Virtual Digital Infrastructure. Digital as a Service focuses in the Digitalization applied to the built infrastructure, or \"Smart Infrastructure\" that eventually will be the foundation of a Smart City or Smart Country where their independent elements and systems are interconnected, integrated and virtualized.