# Classification of Systems and Maintenance Models
## 3 Classification of Systems  
As noted in Section 1, the design of the system, its purpose, and its operating conditions affect the choice of MRS effectiveness indicators. To classify the systems, we characterized each of the listed generalized properties by using a minimum set of the most significant signs. From a maintenance perspective, the design of a system is primarily characterized by its maintainability. According to [1], \"maintainability is the ability of an item under given conditions of use, to be retained in, or restored to, a state in which it can perform a required function.\" Items that can be repaired are compared with those that cannot be repaired because of planned obsolescence. The division of systems into repairable and non-repairable systems is associated with the possibility of restoring an operable state through repair, which is ensured during the development and manufacture of the system. We should also note that sometimes the term \"repairability\" is used to characterize the ability of a system to be repaired. Maintainability and repairability are similar. The only distinction is that while repairability is limited to active repair time, maintainability is based on total downtime (which includes administrative time, active repair time, and logistic time). In addition, the term \"maintainability\" is standard [1], while the term \"repairability\" is not. The concept of \"purpose of the system\" primarily relates to the functions it performs. However, this concept includes not only the list of functions performed but also the relative importance of these functions. These two circumstances can be characterized by qualitative and quantitative assessments of the events that occur owing to system failure, that is, the consequences of failure and the possibility of their quantitative assessment. The evaluation of maintenance effectiveness is carried out using indicators that depend on the operating time of the system in a given mode of temporary use, which may be continuous or intermittent. That is why, as a sign of the classification that characterizes the mode of operation, we chose the temporary mode of using the system for its intended purpose. Therefore, we classified systems according to the following criteria: maintainability, consequences of a failure, possibility of an economic assessment of the consequences of a failure, and temporary mode of system use. To divide a set of system types into subsets according to the listed signs, it is necessary to select a classification system. Currently, the most common classification systems for information objects are hierarchical and faceted [77]. A hierarchical system is used when a subordination relationship is established between the classification signs used at levels \(i\) and \((i+1)\). With a faceted classification system, we subdivide the initial set of objects into subsets by combining the values of the independent signs (facets). As shown below, for the four signs under consideration, a subordination relation exists between all features. Therefore, it is necessary to apply a hierarchical classification system with ordinal registration of individual sign values. We determined the values of the classification signs, established a connection between them, and divided the initial set of systems into disjointed subsets as follows. _First classification sign._ A sign of system maintainability \(i\) (\(i=1\): the system is repairable; \(i=2\): the system is non-repairable). When using \"repairable\", we refer to the systems for which the repair is provided in the technical documentation. Non-repairable systems will include systems whose performance cannot be restored owing to design features or whose restoration is not economically feasible. However, for non-repairable systems, maintenance may be provided, including condition monitoring and removal if necessary.