## 7 Discussion and Challenges
### Future Usage: DT Interaction and Enhanced Maintenance Operations
#### 7.3.1. Organisational, Human and Economic Changes  
The O&M phase is one of the most expensive of the building lifecycle [19]; however, there is a lack of evidence in the literature of any real reduction in these costs [40; 90]. Furthermore, authors have observed that most of the professionals are not fully aware of the initial costs and risks involved in implementing a DT, nor are they aware of the amount of initial work needed [29; 47; 90]. Therefore, there is a need to provide clearer and more precise evidence of the financial benefits that these technologies can bring in the long term and thus to establish use-cases that take into account the initial implementation costs. [PERSON] and [PERSON] have also observed that, while most of the papers are focused on _why_ the professionals should implement these technologies, few explain _how_ these can be implemented in their existing processes [90]. Some changes are needed in the organisational and managerial structure of the O&M phase when it is decided to implement these technologies [29; 47; 90], such as the early involvement of those responsible for the operation to identify the information that will need to be retained throughout the life of the building. Many authors have observed the need for early consideration of maintenance needs [25; 29; 33; 35; 36; 47; 91]. It seems that the O&M phase is often overlooked during the building design and construction. However, these phases contain many useful data for the maintenance process (e.g., geometrical information, equipment placement, construction modifications) [28; 29; 30; 35; 40; 42]. BIM can be used in those phases to retrieve the information needed in an intuitive way, such as linking the information to the 3D representation of the equipment to access it by interacting with the 3D model [28; 29; 30]. However, even when the BIM is used to create a DT, it is still needed to allow communication between the actors of the different phases to define which information must be transferred throughout the building lifecycle [35]. However, this can be complicated because the actors involved in the operation of a building may not yet have been defined when the design or construction phase was started. Thus, it may be interesting to consider a method to automatically define the essential data for the whole life of the building. This definition may be done using AI or ML algorithms fed with known maintenance information from previous, existing buildings. It has been observed that the adoption of new technologies in existing processes can be complicated for users [78]. It is therefore necessary to create new strategies to implement them [41; 86]. Several of the concept papers we retrieved in this research proposed methodologies for implementing DT and the various I4.0 technologies \begin{table}
\begin{tabular}{c c c} \hline \hline
**Category** & **Challenges** & **Reference** \\ \hline \multirow{6}{*}{Organisational, human and economic changes} & Implementation & [29; 41; 90] \\  & Data selection & [25; 29; 33; 35; 36; 47; 91] \\  & Information on financial risks & [35; 90] \\  & New technical skills & [78; 86; 91] \\  & Define roles & [36; 47; 92] \\  & Collaboration management & [16; 22; 25; 29; 32; 33; 38; 40; 41; 65; 69; 70; 72; 78; 79] \\ \hline \multirow{6}{*}{Data management} & Lack of data for DT creation & [21; 32; 37; 38; 49; 61; 74] \\  & and update & [28; 33; 34; 28; 35] \\ \cline{1-1}  & Lack of data standards & [26; 31; 37; 51; 54; 92] \\ \cline{1-1}  & Data ownership & [31; 35; 46; 54; 64; 72] \\ \hline \multirow{2}{*}{Challenges in using XR devices} & Ergonomic and physiological issues & [25; 84] \\ \cline{1-1}  & Calibration & [25; 26; 53; 66; 71; 72; 77; 80; 81] \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Categorical review of the new needs for correct implementation. [22; 28; 29; 33; 34; 36; 39; 41; 42; 45; 46; 51; 57; 62; 64; 81; 86; 90; 93]. For example, [PERSON] et al. proposed a methodology to implement a BIM-based DT on a building with incomplete as-built data [34].