## 3 BIM and DTs--Latest Development Trends and Challenges
### Designing, Modeling, and Control as Services  
The dynamic shaping of the usable and functional environment of buildings requires a change in approach to the organization of BMS systems with FM elements, in particular, the implementation of DT structures as technical solutions that facilitate the effective development of building and BACS functions and services. One of the unobvious trends emerging in the market is the concept of the digital twin as a service (DTaaS), which refers to the use of DT models in the cloud. The idea is that customers will use an online platform, paying only for the services they use without having to maintain their own infrastructure. The cloud platform on which the DT tools are stored is made available to users. The data are transmitted from BACS devices, BIM models, and IoT sensors. The platform is responsible for integrating the data and creating a real-object model for customer use. The DTaaS offers a range of applications, from design and construction to industry. The tool is beneficial in the management of buildings, monitoring user comfort and parameters such as energy consumption [28]. Furthermore, the application can also be useful during the ordinary maintenance of a building, supporting and communicating the need for maintenance, anticipating failures, and planning repairs [26; 27; 55; 67; 68; 69]. One of the most significant benefits of using the DTaaS is the potential for saving time, resources, and money. It has much lower initial costs by not needing to invest in servers and software. The customer is not required to possess the specialist knowledge typically provided by the service provider and platform [24; 59; 70]. Moreover, according to [PERSON] et al. [25], companies using these services definitely have a competitive advantage through better management and monitoring of their facilities. Such solutions can be tested in a virtual environment, aiming to accelerate innovation. By optimizing resources and energy consumption, they remain \"green companies\" and reduce their environmental impact. Considering the mentioned BaaS frameworks, the DTaaS approach also aligns with the development trend of virtualization of BMS and FM platforms (emerging issues in the BMS \"cloudification\" endeavor) and transferring the functions of collecting, processing, and analyzing data from distributed automation and IoT networks to cloud services [71; 72; 73]. It is important to note that the exponential growth of ICT technology has a profound impact on the evolution trends of modern network automation systems in both the industrial and building sectors. In recent years, there has been a fruitful convergence of different technologies, microelectronics, and building systems towards an IP-based infrastructure supported by proprietary communication protocols as well as ethernet and Internet networks. Technological convergence in the management of buildings and smart buildings is accelerating with the increasing deployment of IP-based devices within the IoT. According to [74], building systems used and still are using various protocols, networks, and cable systems. This is evidently an inefficient approach from both an implementation and a management perspective. The IoT concept, which is now being used more and more often, will further enhance, standardize, and expand the functions and scope of BACS services. BMS systems are systematically and consistently switched to IP networks (which also allow remote monitoring of many buildings through a central operations center). The growth of the IoT is being driven by a sharp decline in the cost of advanced sensors, computing power, and data storage along with increasing device density (and decreasing device size) [11; 72]. The IoT can support BIM and DTs by collecting building status data, monitoring performance, predicting failures, automating tasks, and personalizing the environment. Combined with BIM and DTs, the IoT can create smarter, more efficient, and more sustainable buildings [32; 75].