Deductive analysis

To give a thorough, rational review of the field of chemical micro-process technology itself, one ideally would like to follow a deductive analysis route, pursuing a bottom-up approach. First, one may provide a definition of micro reactors, then search for the impacts on the engineering of chemical processes, and try to propose routes for exploitation, i.e. applications. Alternatively, for a less comprehensive, but more in-depth description, one could use a top-dovm approach starting with a selected application and try to design an ideal micro reactor for this. 

The theory of autopoiesis is based on the observation of the actual behavior of a living cell. As such, it is not an abstract theoretical model for life - there are many of these - but a deductive analysis of life as it is on Earth. It is in a way a picture of the blue-print of cellular life, and it is fascinating to see how many concepts related to the process of life - emergence, homeostasis, biological autonomy, interactions with the environment, cognition, evolutionary drift, etc. - pour forth from this analysis in a coherent way. 

This type of hazards analysis can be either deductive or inductive. A deductive (top-down) analysis is one that first defines an undesirable event, and then considers what events and chains of circumstances are needed to occur before the overall undesirable event occurs. A deductive approach is used by detectives to solve crimes. A widely used type of deductive analysis in process risk analysis is the fault tree method, described in the next chapter. 

Risk can be analyzed in one of two basic ways inductively or deductively, that is either bottom-up or top-down. In a deductive analysis a system failure is postulated. The analyst then works backward to deduce what combinations of events could have occurred for the system failure to have taken place (a detective solving a crime is thinking deductively). Fault tree analysis (FTA), the topic discussed in this section, is deductive. An inductive analysis works in the other direction. A single failure, such as a pmnp stopping or a valve closing at the wrong time, is postulated. The... 

The FTA is a diagrammatic analytical technique that is used for ReUabiUty, Maintainability and Safety Analysis. It is a top-down (deductive) analysis, proceeding through successively more detailed (i.e. lower) levels of the design until the probability of occurrence of the top event (the feared event) can be predicted in the context of its enviromnent and operation. 

Analytical trees force individuals to use the deductive analysis process and to think about the events that must occur at lower levels for output events to be generated. 

An approach to fault tree analysis. (A) External boundary resolution limit, (B) deductive analysis—FTA. 

The typical failure analysis itself only happens in the third step. Steps 1 and 2 are analyses and information, which are needed in FMEA in order to present the object of analysis or are other analysis by themselves. Steps 1-3 could be seen as the illustration of a deductive analysis, since functions and structures are broken down or decomposed (Fig. 4.31). 

Reliability block diagrams are, similar as the fault tree analysis, are considered in ISO 26262 as example for deductive analysis. The blocks can be logically put into relations through Boolean algebra. If the blocks are quantified, the relations can also be described mathematically, whereas such descriptions are used as a foundation for formal description models. The simplest quantitative method is a simple summing up of the failure rates of the individual components of a function. The method is also called Part Count Method , which simply based on an addition of failure rates of electric parts. 

Generally, it is only possible to conduct a functional analysis as a top down approach since the function of a certain hardware element needs to be known first before the cause of failure can be derived. On the other hand, for the failure observation of sheer technical (realized) elements, such as components or structural elements, the failure of elements and also random hardware failures can be inferred from the characteristics of the elements. The failure effects can then be referred to as inductive analysis. However, as a result only the inductive analysis truly addresses the effects of random hardware failure. By a deductive approach only requirements for random hardware-failure could be elaborated so that required failure rates and related diagnostics could be specified. By adequate verifications and tests the fulfillment of given metric requirements could be shown. This will widely indicate a mix of inductive and deductive analysis, whereas the lower level is designed inductively and in the upper level the technical malfiinctional behaviour is described functionally, so that the consistency (see Figs. 4.35 and 4.36 analysis phase) could be assured. 

Basically, the inductive and deductive safety analyses are invoked in the architecture related chapters of ISO 26262, in which the inductive analysis is often demanded for all ASBL requirements and the deductive analysis only for ASIL C and D safety requirements. 

All requirements of ISO 26262 from part 5, Chap. 7 could be covered through the Design-FMEA, if the step of the function to the failure cause would be accepted as deductive analysis. The question now is if it is possible with a Design-FMEA to... 

The deductive analysis is in ISO 26262 required in additions to the inductive analysis for ASIL C and D elements. The aim in this case is to have a second independent analysis method, which analyzes the product independently from top-down and bottom-up. Therefore, the combination of the inductive analysis in one step with the deductive analysis is not well accepted. An automatic transformation of one analysis result into another illustration is also not expedient for safety. Therefore an alternative approach based on Reliability Block Diagrams could be considered. 

The aim of the deductive analysis is primarily to detect possible failure before design decisions are made. Therefor the deductive analysis should be parallel during the developing and detailing of requirements, e.g. on the descending branch of the V-cycle. 

The inductive analysis would consequently be the verification to see whether a design decision etc. is for example sufficient, appropriate, or adequate. This means that in the first iterations of the deductive analysis only information are available, which is derived from requirements, constraints etc. liom higher abstraction levels. These could also be environmental conditions, systems or operation modes and architecture or design decisions or assumptions. This deductive analysis is required for ASIL C and D in the product development on system level (Part 4 of ISO 26262) and on hardware level (Part 5 of ISO 26262). 

Therefore we have the possibility to use the block diagrams for the functional dependency analysis. The dependencies through the technical realization are again to be considered by deductive analysis. 

The analysis of the failure types is very essential (error or failure modes, possible error behavior of characteristics of elements etc.). ISO 26262 mentions indications in the correlating appendices of parts 5 (attachment D) and 6 (attachment D) for the safety mechanisms, which need to be implemented. For a deductive analysis we can only determine the possible failure modes from the function, the characteristics of the function (parameter) as well as their relation to the environment. Error modes like no function, an incorrect function afimction too low or too high or drifts can be evaluated in the context of their Diagnostic Coverage for electronic parts (DC). Furthermore, sporadic (intermittent or transient) failure, oscillations or other dynamic failure are derived from the specified intended functions and their characteristics. How and in what way these errors propagate, depends on environmental conditions. Thus, in a... 

At least during the verification of the technical safety concept the result of the inductive and deductive analysis need to be merged. Which technical failures propagate further upwards to the safety goals in what way, how likely, and with which intensity, is then shown in the overall safety assessment, when all verification, integration and validation results are available. 

However, the deductive analysis does not start at the point at which ISO 26262 first required it but already in the requirement analysis. Each Chap. 6 of the parts 4, 5 and 6 requires a verification of the requirements. Additionally, part 8 of Chap. 6 requires that the safety requirements are specified in natural language and in formal or semi-formal notations. Whereas according to the glossary of ISO 26262 the formal notation is a syntactically and semantically complete notation and the semi-formal notation is only a syntactically complete notation. 

Even for a deductive analysis completeness analysis all error impacts is an important argument. Of course, each possible error, fault or malfunction found will help to improve the quality of a product, but for safety, completeness is required. This is why the failure analysis in the VDA-FMEA is at step three after the product and function decomposition. This means that for each function of a stiucture element the possible malfunctions need to be identified. For verification of the safety-relevant requirements it is important to first analyze, whether the possible malfunction, which can lead to a malfimctional behavior, have been completely identified. For a mere functional analysis stating that data flow, signals or information just could have 2 error states ... 

However, the model-based safety analysis should first be seen as addition for the classic analysis methods. It would be worth considering seeing the model-based safety analysis preferably as deductive analysis and the classic FMEA further on as inductive analysis. Therefore, the systematic approach of consistent system engineering can again be applied from the vehicle level all the way down to the silicon stmcmres and the software development. 

A deductive analysis is one that would conclude no more than the data provides. The specific causal factors supporting the conclusion must be identified and established, and then the conclusion will be true. It seems like reverse logic however, the hazard can be validly deduced only from the specific detailed causal factors. Deductive and inductive quaUties have become intangible attributes of HA techniques. An inductive analysis would be used to broadly identify hazards without proven assurance of the causal factors, while a deductive analysis would attempt to find the specific causal factors for identified hazards. An inductive analysis can be thought of as a what-if analysis. The analyst asks, what if this part failed, what are the consequences. A deductive analysis can be thought of as a how-can analysis. The analyst asks, if this event was to occur, how can it happen or what are the causal factors ... 

Deductive analysis tends to be a top-down approach (going from the general to the specific) and an example of this is the FTA methodology. An FMEA is just the reverse, it goes from the specific to the general and is known as an inductive analysis. 

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