diff --git a/component_failure_modes_definition/component_failure_modes_definition.tex b/component_failure_modes_definition/component_failure_modes_definition.tex
index abd4889..e0bcc94 100644
--- a/component_failure_modes_definition/component_failure_modes_definition.tex
+++ b/component_failure_modes_definition/component_failure_modes_definition.tex
@@ -15,6 +15,104 @@ for a given type of part can be obtained from standard literature\cite{mil1991}
 \cite{mech}. %The failure modes for a given component $K$ form a set $F$.
 
 
+
+
+\subsection{Systems, functional groups, sub-systems and failure modes}
+
+It is helpful here to define some terms, `system', `functional~group', `component', `base~component' and `sub-system'.
+
+A System, is really any coherent entity that would be sold as a safety critical product.
+A sub-system is a system that is part of some larger system.
+For instance a stereo amplifier separate is a sub-system. The 
+whole Sound System, consists perhaps of the following `sub-systems': 
+CD-player, tuner, amplifier~separate, loudspeakers and ipod~interface.
+ 
+%Thinking like this is a top~down analysis approach
+%and is the way in which FTA\cite{nucfta} analyses a System
+%and breaks it down.
+
+A sub-system will be composed of component parts, which
+may themselves be sub-systems. However each `component part'
+will have a fault/failure behaviour and it should
+always be possible to obtain a set of failure modes
+for each `component'. 
+
+If we look at the sound system again as an
+example; the CD~player could fail in serveral distinct ways, no matter
+what has happened to it or has gone wrong inside it.
+
+
+Using the reasoning that working from the bottom up forces the consideration of all possible
+component failures (which can be missed in a top~down approach)
+we are presented with a problem. Which initial collections of base components should we choose ?
+
+For instance in the CD~player example; to start at the bottom; we are presented with
+a massive list of base~components, resistors, motors, user~switches, laser~diodes all sorts !
+Clearly, working from the bottom~up we need to pick small
+collections of components that work together in some way.
+These are termed `functional~groups'. For instance the  circuitry that powers the laser diode
+to illuminate the CD might contain a handful of components, and as such would make a good candidate
+to be one of the base level functional~groups.
+
+
+In choosing the lowest level (base component) sub-systems we would look 
+for the smallest `functional~groups' of components within a system. A functional~group is a set of components that interact
+to perform a specific function.
+
+When we have analysed the fault behaviour of a functional group, we can treat it as a `black box'.
+We can now call our functional~group a sub-system. The goal here is to  know how will behave under fault conditions !
+%Imagine buying one such `sub~system'  from a very honest vendor.
+%One of those sir, yes but be warned it may fail in these distinct ways, here
+%in the honest data sheet the set of failure modes is listed!
+This type of thinking is starting to become more commonplace in product literature, with the emergence
+of reliability safety standards such as IOC1508\cite{sccs},EN61508\cite{en61508}.
+FIT (Failure in Time - expected number of failures per billion hours of operation) values
+are published for some micro-controllers. A micro~controller
+is a complex sub-system in its self and could be considered a `black~box' with a given reliability.
+\footnote{Microchip sources give an FIT of 4 for their PIC18 series micro~controllers\cite{microchip}, The DOD
+1991 reliability manual\cite{mil1991} applies a FIT of 100 for this generic type of component}
+
+As electrical components have detailed datasheets a useful extension of this would
+be failure modes of the component, with environmental factors and MTTF statistics.
+
+Currently this sort of information is generally only  available for generic component types\cite{mil1991}.
+
+ 
+%At higher levels of analysis, functional~groups are pre-analysed sub-systems that interact to
+%erform a given function.
+
+\vspace{0.3cm}
+%\begin{table}[p]
+\begin{tabular}{||l|l||} \hline \hline
+  {\em Definition } & {\em Description}    \\ \hline
+System & A product designed to  \\
+       & work as a coherent entity  \\  \hline   
+Sub-system & A part of a system, \\
+           & sub-systems may contain sub-systems \\    \hline 
+Failure mode & A way in which a System, \\
+             & Sub-system or component can fail \\     \hline  
+Functional Group & A collection of sub-systems and/or \\
+                 & components that interact to \\
+                 & perform a specific function  \\    \hline  
+Failure Mode     & The collection of all failure \\
+Group            & modes from all the members of a \\
+                 & functional group \\ \hline
+Base Component & Any bought in component, which \\
+               & hopefully has a known set of failure modes  \\    \hline  
+ \hline
+\end{tabular}
+%\end{table}
+\vspace{0.3cm}
+
+\begin{figure}[h]
+ \centering
+ \includegraphics[width=400pt,bb=0 0 680 500,keepaspectratio=true]{./fmmd_uml.jpg}
+ % fmmd_uml.jpg: 680x500 pixel, 72dpi, 23.99x17.64 cm, bb=0 0 680 500
+ \caption{UML respresentation of Failure Mode Data types}
+ \label{fig:fmmd_uml}
+\end{figure}
+
+
 \subsection{Unitary State Component Failure Mode sets}
 
 An important factor in defining a set of failure modes is that they
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diff --git a/symptom_abstraction/symptom_abstraction.tex b/symptom_abstraction/symptom_abstraction.tex
index 66de095..72789e8 100644
--- a/symptom_abstraction/symptom_abstraction.tex
+++ b/symptom_abstraction/symptom_abstraction.tex
@@ -39,7 +39,7 @@ This paper focuses on the process of building the blocks that are used in the hi
 \section{Introduction}
 
 Fault finding is intinctively performed from the top-down.
-A faulty peice of equipement is examined and will have a 
+A faulty piece of equipment is examined and will have a 
 symptom or specific fault. The area or sub-system within the 
 equipemnt will next be looked into. Secific measurements
 and checks will be made, and finally a component or a low level sub-system
@@ -154,13 +154,13 @@ System & A product designed to  \\
        & work as a coherent entity  \\  \hline   
 Sub-system & A part of a system, \\
            & sub-systems may contain sub-systems \\    \hline 
+Failure mode & A way in which a System, \\
+             & Sub-system or component can fail \\     \hline  
 Functional Group & A collection of sub-systems and/or \\
                  & components that interact to \\
                  & perform a specific function  \\    \hline  
 Base Component & Any bought in component, which \\
                & hopefully has a known set of failure modes  \\    \hline  
-Failure mode & A way in which a System, \\
-             & Sub-system or component can fail \\     \hline  
  \hline
 \end{tabular}
 %\end{table}