Requirements Allocation

Proteln-conq>lexlng polyphenols are broadly effective against herbivores, especially those not specifically adapted to eat plants containing polyphenols (47). They may constitute 10% or more of the leaf dry weight (12, 37, 44), and this requires allocation of significant amounts of carbon and energy to their construction. The use of limited reserves for such quantitative defenses must be balanced against the requirements of rapid canopy development and new shoot extension. 

The standard gives guidance on E/E/PE Systems. The goal may be achieved by more than one safety-related system and by a bundle of measures, but always based on hazard and risk analysis, on getting the overall safety requirements right, and by developing a concept for proper safety requirements allocation. 

Definition and Implementation of Security Policy ([l]-[5], from Concepf to Security Requirements Allocation )... 

Consequently, the draft Consultation NAP published in January 2004 comprised allocations based on historical emissions shares to 867 installations divided into fourteen different sectors (compared to 1,054 installations and fifty-two sectors in the final NAP). In addition, there were sixteen incumbent sites for which insufficient data were available from which to calculate an allocation (these were sites that began operation in 2003). Finally, there were fifteen named new entrant installations that were expected to require allocations but for which no allocation was proposed because there had been no decision on how new entrant allocations would be determined. 

Design phase. During the design phase, task scenarios, prototypes, and simulations are used to detail and refine the task procedures, task requirements, allocation decisions, and human-machine interface design. 

Processes. Kerrel and Ferrell (2001) advise that DO-178B specifies the information flow between system processes and S/W processes. The focus of the information flow from the system process to the S/W process is to keep track of requirements allocated to S/W, particularly those requirements that contribute to the system safety. The focus of information flow from the S/W process to the system process is to ensure that changes in the S/W requirements, including the introduction of derived requirements (those not directly traceable to a parent requirement), do not adversely affect system safety. 

Requirements Engineering (also known as System Engineering) is the process of eliciting individual stakeholder requirements and needs and developing them into detailed, agreed requirements documented and specified in such a way that they can serve as the basis for all system development and certification activities. There are three core activities associated with robust Requirements Engineering, which are requirements allocation (see the following sections), requirements validation (see Step 2) and requirements verification (see Step 3). These are illustrated in Fig. 1.3. 

Requirements Allocation is the process of ensuring that all requirements are assigned to each level of system integration. All requirements (including the allocated FDAL) are cascaded down the system hierarchy and, along with the derived equipment, provide the contents of the applicable system-level specifications (see Fig. 1.3). 

With respect to requirements allocation to SAV/hardware, the identification and allocation of behavioural safety requirements in the context of the system are fundamental to the realisation of acceptably safe systems in aircraft. There are numerous approaches to identify these specific behaviour safety requirements, for instance ... 

With reference to Section 9.2.22, this is where we ensure that the integrated altitude display system has requirements allocated to each level of abstraction (refer to Fig. 1.3). 

With reference to Figs 1.8 and 1.9, if we specifically look at the components making up the altitude display system, then we will probably find that the PFD is an ETSO item (see ETSO-ClOb). If we then purchase an item with ETSO approval, we do need to tailor our requirements allocation approach by considering three aspects ... 

Evidence of the acceptability of any lifecycle data provided by SAV or hardware processes to the system processes, including evaluations of derived requirements for impact on SSA and system reqnirements and issues raised by SAV or hardware processes in relation to system requirements allocated to SAV or hardware. 

Installation, ergonomic and environmental requirements allocated to SAV or hardware. 

High-Level S/W Requirements are SAV requirements developed and defined from analysis of system requirements, safety-related requirements and system architecture they are predominantly specified at an abstraction that is usually independent of the SAV architecture and target computer. High-Level SAV Requirements are the first level of requirements specified when capturing system or subsystem requirements allocated to SAV. 

The enterprise assesses possible alternative subfunction arrangements for the decomposition of a function and for the allocation of allocable performance requirements to the subfunctions during functional analysis. Functional trade-off analyses and assessments are performed to identify the recommended set of subfunctions for each function and performance requirement allocations in terms of risk, cost, schedule, and performance impacts. 

According to lEC 61508 and lEC 61511 the safety validation should be performed in terms of the overall safety functions requirements and the overall safety integrity requirements, taking into account the safety requirements allocation for the E/E/PE safety-related system in designing. In particular PFDavg value has to be verified in the probabilistic modeling process for the architectures considered of the E/E/PE safety-related systems taking into accoimt the probabihstic interval criterion for selected SIL. 

Operation of a reactor requires allocation of certain responsibilities, functions and duties. In principle these are the same as for a power reactor. However the design of a small reactor may allow a different allocation, while maintaining the essential requirements of public safety, plant reliability and low cost. For example, the design may reduce the need for prompt local response, and allow operating duties either to be centralized away from the reactor, or dispensed with entirely. The latter case requires confident demonstration of inherent safety. 

While designing automotive systems, it will be indispensable to trace the dependencies between artifacts of the EEA, the allocated safety requirements and the ASILs according to which the architecture elements have to be developed later on. Based on the specification of model query rules, the EEA model can be browsed for chains of artifacts in a specific relationship. Based on this, for example all hardware elements involved in fulfilling a SG, all functions assigned to a specific ASIL, or all artifacts having the same safety requirement allocated, can be determined. The results of these model query rules can be displayed to support the overview of the dependencies. 

Traceability is required between system requirements allocated to software, software requirements and source code (also between source code and object code for Level A), and between software requirements and test cases. This enables verification that all the requirements have been implemented and that there is no undocumented code. 

The overall life cycle discussions in the standard mainly covered in this main Clause 7, having 17 major sub-clauses. Now coming back to main life cycle phases in Fig. VI/4.0.2-1, it is seen that the first part of the safety life cycle is basically the analysis part comprising concept, scope for the system/EUC, hazard/risk analysis, creation of overall safety requirements, and identification of specific safety functions to prevent the identified hazards safety requirements allocation. The middle part is realization activities (Clause 7.10) as detailed in Figs. Vl/4.1.4-1 and Vl/4.1.4-2, are dealt with in Parts 2 and 3 discussions. The next part of the life cycle is related to installation and commissioning (Clause 7.13). Then comes the validation (Clause 7.14), operation and maintenance (Clause 7.15), modification, retrofit (Clause 7.16), and finally, decommissioning (Clause 7.17). 

To demonstrate the method we will use a small part of a larger safety life cycle work done on an electronic parking brake (EPB) item [10]. No assertion to comprehensiveness is being made on the item presented here. We have conducted the process prescribed in ISO 26262 with a minimal but illustrative example. The goal is to have a set of technical safety requirements allocated to the platform that states that some platform mechanism has to behave in a certain way, with ASIL integrity. Then use a call trace in the requirement annotated executable model of the relevant modules to yield a complete list of the affected AUTOSAR requirements for the technical safety requirement of interest. 

Tag Technical Safety Requirement Functional Safety Requirement Allocated ASIL... 

---