## 2 State of the Art
### Maintenance, Reliability, and Availability  
Maintenance, reliability, and availability are essential tools to prevent failures, damages, and delays in the production processes and services in terms of time, costs, and systems' performance. The quality management effort for internal and external customer's satisfaction, guided by the international norms and world conventions, takes advantage of the research relating to hospital physical assets to support new ideas relevant to further improvement like the following authors described. [PERSON] et al. (2019) stated that \"to develop a safety and profitable process, uncertainty quantification is necessary for a reliability, availability, and maintainability (RAM) analysis. The uncertainties of 3% in each key decision variable are propagated, bringing the system into an unreliable/risk region. This approach reduces about 90% of the total computational time when compared with the conventional simulation approaches required for a complex first principle-based model\" ([PERSON] et al., 2019). [PERSON] et al. (2019) stated that the \"reliability model is based on the information available in the maintenance system--driven framework using both classical and Bayesian methodologies. It illustrates the ageing process and the necessary data for the creation of the model. This model can be demonstrated and analysed with an important factor; it represents the flexibility to build the reliability expected during the maintenance strategy-making and the knowledge of the equipment\" ([PERSON] et al., 2019). [PERSON] (2016) stated that \"RAM analysis is the basis for complex system performance analysis. To demonstrate such a methodology, the RAM analysis steps, such as scope definition, lifetime data analysis, modelling, simulation, critical analysis, sensitivity analysis, and conclusions, will be discussed\" ([PERSON] et al., 2019). [PERSON] and [PERSON] (2015) stated that \"system reliability, mean time to failure, and steady-state availability, are functions of the component failure rates. The primary objective is providing explicit expressions for these performance measures and obtaining various characterizations on their mathematical structures\" ([PERSON] et al., 2017). [PERSON] et al. (2017) stated that \"the complex of RAM factors constitutes a strategic approach for integrating reliability, availability, and maintainability, by using methods, tools and engineering techniques (Mean Time to Failure, Equipment Down Time and System Availability values) to identify and quantify equipment and system failures that prevent the achievement of productive objectives\" ([PERSON] et al., 2017). [PERSON] (2010) suggested that \"Reliability is defined to be the probability that a component or system will perform a required function for a given period when used under state operating conditions\" and that \"Maintainability is defined to be a probability that a failed component or system will be restored or repaired to a specified condition within a period when maintenance is performed following prescribed proceduresand Availability is defined as the probability that a component or system is performing its required function at a given point in time when used under state operation condition\" [20]. [PERSON] et al. (2011) stated that \"many problems have existed in synthesis of design of Reliability, Maintainability, Supportability (RMS) and performance; such as RMS design activities are numerous and optional, variable feedback branches can satisfy same RMS requirement, some iteration among RMS and Performance activities is necessary, and many uncertainties exist in the design process\" [21]. [PERSON] et al. (2011) stated that \"the need, method, benefits, and possible areas of application for the proposed RAM database have been identified. Both the technical and managerial challenges were outlined, which could be encountered during this database's realisation. The structure for the database is suggested keeping in view the implementation of RAM concepts quickly and efficiently\" [22].