# Seeking a Definition of Digital Twins for Construction and Infrastructure Management
## 5 Defining and Standarising the Concept of a Digital Twin for the Built Environment  
### Creation of a European Standardisation WG for Digital Twins  
During the SPHERE EU project (GA No. 820805), a new association was born with the name of the Building Digital Twin Association (BDTA). Based in Belgium, this association aims to develop new standards to enable interoperability and advanced simulation applications in DTs. The first step is to clearly define the meaning and scope of DTs in the construction industry. Following one of the white papers published during the Sphere project execution, some definitions were presented [52]. In 2021, the SPHERE project contacted the Spanish Association for Standardisation, UNE, to develop a standardisation document with the results of the project. Several options were assessed, including a CEN Workshop Agreement (CWA) [53]. The activities and ongoing projects of existing standardisation groups were reviewed at the international (ISO and IEC) and European (CEN/CENELEC) level in order to establish a group dealing with DTs in the AECOO (Architecture, Engineering, Construction, Owner Operator) sector:  
* International level: ISO/IEC JTC 1/SC 41, \"Internet of things and digital twin\", which had an existing WG 6 for DTs; ISO/TC 59/SC 13 for BIM; and ISO/TC 184/SC 4, \"Industrial data\", which had several standards and projects for DTs in manufacturing, like the ISO 23247 set of standards. * European level: CEN/TC 442 building information modelling (BIM). The preferred option was to create a group in CEN, as European EN standards are a very important advantage for the dissemination of the results: all CEN members must adopt them as national standards before the withdrawal of any conflicting standards [54]. Furthermore, once the project of a European standard is registered, CEN members cannot develop a national standard for the scope of the proposed EN, due to the \"standstill\". In addition, SPHERE was a European project, and the Building Digital Twins Association (BDTA) was focused on the European market. Thus, the decision was to create a new working group (WG) for DTs in the built environment in the existing committee for BIM (CEN/TC 442). To assess the feasibility of this new WG, a presentation was made during the plenary meeting of CEN/TC 442 in November 2021 [55]. After the positive feedback during the meeting, a formal proposal for a new WG was presented by UNE, which was balloted and approved, creating the CEN/TC 442/WG 9, \"Digital twins in the build environment\", in April 2022, with [PERSON] (BDTA) as Convenor and [PERSON] (UNE) as Secretariat. The kick-off meeting took place in April 2022 and the activation of a European project covering definitions and framework was discussed. During the meetings of 2022, the state of the art for DTs was evaluated and, in the meeting held in December, it was considered necessary to start with an analysis of the actual use cases of DTs in Europe. Thus, a proposal for a new technical report was launched for ballot in January 2023 and approved in March. To gather existing use cases, a template was circulated in March 2023 [56]. Before the deadline (27 April 2023), a total number of 37 use cases were gathered, and some more after that deadline, including office and residential buildings, schools, airports or train stations, roads and railways, bridges, etc. The use cases were shared in the working group and a reduced task group made an initial assessment and, where necessary, contacted the authors to gather additional information to facilitate an understanding and benchmarking of the different cases. The working group reviewed the results at regular meetings and the final decision on acceptance was based on the completeness of the content and the clarity of the information provided. The final text included 34 selected use cases and an assessment of the main and secondary uses of the DT, including construction optimisation, operation optimisation, marketing, training, etc.