Functional Analysis and Allocation
Functional Analysis and Allocation is a top-down process of translating system level requirements into detailed functional and performance design criteria. The result of the process is a defined Functional Architecture with allocated system requirements that are traceable to each system function.
SMC Systems Engineering Handbook – Figure15: Functional Analyss and Allocation
The Functional Analysis and Allocation bridges the gap between the high level set of system requirements and constraints (from the Requirements Analysis) and the detailed set required (in Synthesis) to develop or purchase systems and implement programs. It is an integral part of both the Requirements Loop and the Design Loop. During this activity, an integrated Functional Architecture is defined in sufficient depth to support the synthesis of solutions in terms of people, products, and processes, and to allow identification and management of attendant risk. It is an iterative process, interacting and reacting to the ongoing activities in the both the Requirements and Design Loops. 
The initial step is to identify the lower-level functions required to perform the various system functions. As this is accomplished, the system requirements are allocated and functional architecture(s) are developed. These activities track and interact so that as details evolve, they are continually validated against each other. Should anomalies occur, alternate architectures and allocations may be carried through early stages of this activity until the optimum approach becomes apparent. The internal and external functional interfaces are defined as the architecture matures. The functional architecture(s) and their companion functional requirements are the input to the Synthesis activity. Completing the Design Loop, the detailed results of the Synthesis are compared to the candidate architecture(s) and allocated requirements to help zero in on the optimum approach and to assure that all proposed solutions meet established requirements. 
Decomposition: to lower-level functions is the incoming interface for the Requirements Loop. The functions identified in the Requirements Analysis are analyzed to define successively lower-levels of functions that accomplish the higher-level functional requirements. Alternate lower-level functional solutions covering all anticipated operating modes are proposed and evaluated to determine which provides the best fit to the parent requirements and best balance between conflicting ones. The initial decomposition is the starting point for the development of the functional architecture and the allocation of requirements to the lower functional levels. Adjustments to the decomposition strategy may be necessary as details are developed. 
Allocation: All requirements of the top-level functions must be allocated for all lower level functions. Traceability is an on-going record of the pedigree of requirements imposed on system and subsystem elements. Because requirements are derived or apportioned among several functions, they must be traceable across functional boundaries to parent and child requirement .Traceability allows the System Engineer to ascertain rapidly what effects any proposed changes in requirements may have on related requirements at any system level. The allocated requirements must be defined in measurable terms, contain applicable go/no go criteria, and be in sufficient detail to be used as design criteria in the subsequent Synthesis activity. 
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