\begin{abstract}
In failure mode analysis, it is essential to
know the failure modes of the sub-systems and components used.
This paper outlines a technique for determining the failure modes of a sub-system given 
its components.
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This paper describes a process for taking a functional~group of components,
applying FMEA analysis on all the component failure modes possible in that functional~group,
and then determining how that functional group can fail.
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With this information, we can treat the functional group
as a component in its own right.
This new component is a derived from the functional~group.
In the field of safety engineering this derived component corresponds to a low~level sub-system.

Once the failure modes have been determined for a sub-system/derived~component,
this derived component can be combined with others to form functional groups
to model higher level sub-systems/derived~components. 
In this way a hierarchy to represent the fault behaviour
of a system can be built from the bottom~up. This process can continue
until there is a complete hierarchy representing the failure mode
behaviour of the entire system under analysis.
%FMMD hierarchy
%Using the FMMD technique the hierarchy is built from the bottom up to ensure complete failure mode coverage.
Because the process is bottom-up, syntax checking and tracking can ensure that
no component failure mode can be overlooked.
Once a hierarchy is in place it can be converted into a fault data model.
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From the fault data model, traditional FTA and FMEA models (sub-sets of the fault data model) can be derived if desired.
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%This paper focuses on the process of building the blocks, the symptom extraction or abstraction process, that is key to creating an FMMD hierarchy.
\end{abstract}