## 2 Theoretical Background and Previous Studies
### Previous Studies on BIM-Based Cloud Computing  
Cloud computing technology, developed primarily by IT firms such as Google, Microsoft, Apple, and Oracle, etc., is making its way around different industry sectors in different forms, such as service-type software (SaaS) that provides applications, a platform service (PaaS) that enables creation of software including programming and databases, and infrastructure service (IaaS) like the open API service of Google and Amazon web service. [PERSON] and [PERSON] (2018) developed a tool for benchmarking the function of the VDI system, while [PERSON] and [PERSON] (2018) performed a study that evaluated the operational performance of the VDI. In addition, [PERSON] et al. (2018) conducted an economic feasibility study by applying the VDI system to the hospital setting.  
Recently, the construction sector has also seen an increased application of cloud computing technology in various operations. [PERSON] et al. (2018) conducted a study using an integrated cloud-based Internet of Things platform for asset management of elevated metro rail projects; [PERSON] et al. (2018) developed a mobile application prototype for on-site information management; and [PERSON] (2018) studied a cloud computing adoption strategy to improve BIM utilization at the construction site. [PERSON] and [PERSON] (2018) conducted a study on providing the BIM data for construction sites in real time by utilizing cloud-based RFID technology; and [PERSON] et al. (2018) studied a system that supports urban design by using cloud-based virtual reality (VR) technology. In addition, [PERSON] and [PERSON] (2018) developed a cloud-based bridge monitoring application that stores and utilizes data generated from bridge operations. Regarding BIM cloud service, [PERSON] and [PERSON] (2018) studied the development of a viewer based on the BIM server for a cloud computing-based BIM service, and [PERSON] et al. (2018) conducted research on a mobile BIM-based on-site supervision support tool.  
Specifically, on the study of the cloud computing-based BIM service, [PERSON] and [PERSON] (2018) conducted a survey that asked 32 personnel working in the construction sector in Korea (10 from construction companies, 20 from design and engineering, and two from a professional architectural firm and other, respectively) if it was appropriate to apply cloud computing in the BIM environment. According to the survey results, respondents showed their preference with an average agreement rating of 3.56 out of 5. Particularly, the preference of those who had used cloud service (11 people) was greater at 3.86, compared to the 3.4 assigned by those who had not, indicating that the more popular the BIM cloud service is, the more increased its use could be.  
However, those studies conducted previously considered cloud environment merely as data storage or a server and did not consider the use of it as a resource, which is one of the significant characteristics of the cloud. Moreover, previous studies focused on providing cases of BIM data usage and failed to present sufficient information on the role of the cloud as a platform, in terms of how data are processed, in order to utilize BIM data ([PERSON] et al., 2018; [PERSON] et al., 2018). Recently, studies on managing resources, which take BMI data characteristics into consideration, are under way, but they are limited to specific construction projects, therefore, a further break down of resource allocation methods is necessary ([PERSON] et al., 2018; [PERSON] et al., 2018).  
As such, this study aimed to introduce the BIM-based VDI resource allocation method, which is subdivided by taking into consideration the BIM environment of small to medium-sized design firms, and to validate it after establishing the BIM-based VDI system.