PSI - Issue 22

Jerzy STANIK et al. / Procedia Structural Integrity 22 (2019) 334–344 "Author name" / Structural Integrity Procedia 00 (2019) 000 – 000

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2. Engineering infrastructure model For the purpose of model research as well as control and maintenance of an acceptable level of technical infrastructure (IT) risk, it can be described by the following expression: IT ≡ < , KT, IT, U, A, S, ℤ TO, B, > (4) where: IT - engineering infrastructure treated as a complex object subject to control; - the purpose of IT activity, KT - basic and supporting assets of IT understood as basic IT systems, business processes and various types of assets related to IT operations, IT – engineering infrastructure environment understood as enabling or providing IT with maintenance of the required level of usefulness and risk; U - IT usefulness, understood as a set of features or properties of basic IT elements, A – collection of criteria defining the acceptability of a given risk in relation to individual IT usefulness features or the entire IT, S − set of acceptable control decisions, also called directives or orders, with the help of which one can determine the current properties of basic assets or IT usefulness, ℤ TO – a set of engineering and personal resources available, B – a set of security mechanisms understood as security measures aimed at reducing residual risk by reducing the potential of a hazard system For the considered class of complex objects (IT) the action is understood as: 1) In relation to IT as an ordered pair: DZ IT ≡ < α IT , ℤ Z IT > , (5) where: α IT - the purpose of IT activity, ℤ Z IT - a set of tasks ensuring achievement of the goal α IT ; 2) With regard to the subsystem for control of utility properties as an ordered pair: DZ OIT ≡ < α OIT , S OIT ⊆ S > , (6) where: α IT - the purpose of the control subsystem, S OIT - a set of tasks (controls) ensuring achievement of the goal α OIT . It is assumed that the purpose of the usefulness property control system is to maintain the required level of current usability ̂ ( ) in relation to functional reliability and functional security. This goal can be achieved by the current control of functional configuration resources or security configuration resources. 3. Engineering infrastructure risk When controlling the level of risk, we are only interested in certain, a priori unknown moments in time in which control decisions should be taken. The IT states in such moments in time will be referred to as significant states from the point of view of risk management. We assume that in the time period between each two significant states, it is possible to perform all the tasks from the collection ℤ , resulting from the purpose of IT or its mission. The occurrence of a significant state is caused by the occurrence of a difference between the acceptable risk level and its current residual risk value. This corresponds to the condition: ( ) > . (7) The occurrence of such an event causes transition of the IT transition from the “acceptable” state to the “intolerable” state and is called “IT failure” or “the loss of desired IT usefulness” or “IT transition state”. This transition may be caused by the following events: