Definitions of dependability

The article analyzes dependability-related definitions that have been used so far in a number of regulatory documents, the majority of which have been borrowed into Wikipedia. The analysis shows the shortcomings of said terminology, while more correct definitions of primary dependability-related terms are suggested for dependability, reliability, maintainability, durability, survivability, storageability, operation time, limit state. For instance, the generic term “science” instead of “property of object” is suggested for the definition of “dependability”, as the former better complies with the modern understanding of the term “dependability”, as it has a subject matter, research methods and quite specific goals. It is also shown that this definition of “dependability” may be taken as a basis and then all dependability characteristics should be defined not as “properties of objects”, but rather as dependability indicators, while specifying what properties they characterize. For example, reliability is a dependability indicator that characterizes the time from the start of object operation to its expected failure. Another example: storageability is a dependability indicator that characterizes the time during which an object can be stored under certain storage conditions with no loss of required quality. It is suggested to define in this manner all the required dependability characteristics. Further it is shown that there is an error in the dependability-related definitions with the generic term “property of object”, as the definition in those notions is incorrectly associated with the term it refers to. For instance, the existing definition of dependability: “property of an object to maintain in time and within the set limits the values of all parameters that characterize the ability to perform the required functions in specified modes and conditions of operation, maintenance, storage and transportation” should be associated with the term “dependability of object”, but not “dependability”, as it implies a wider notion. Additionally, the article suggests a number of new terms, such as dependability of object, reliability of object, maintainability of object, etc. that are directly related to the dependability indicators of a specific facility a user is concerned with. In the conclusion examples are given of construction of terms and definitions for such technical objects as control systems. The distinctive feature of such objects is that they are usually multifunctional and it is not correct to set dependability requirements for the system as a whole, as that is impossible. In such cases it is believed that the system’s dependability has been identified when the dependability indicators of all the functions it performs are known.

aspect, safety, time, reliability, time, longevity, survivability, quality, operation time, science, object, definition, limit state, mode, maintainability, property, storageability, term, operational application

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2. GOST 27.005-89 Technology dependability. Basic concepts. Terms and definitions.

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5. NP-026-04 Requirements for safety-critical control systems of nuclear powerplants.

6. GOST 29075-91 Nuclear instrumentation systems for nuclear powerplants. General requirements