Initial updates to L13 on module decomp - exceptions, assumptions, qualities of design

Lectures/L13_ModuleDecomposition/ModuleDecomposition.tex

@@ -13,6 +13,8 @@
 
 \usepackage{booktabs}
 
+\usepackage{listings}
+
 \useoutertheme{split} %so the footline can be seen, without needing pgfpages
 
 % \pgfpagesuselayout{resize to}[letterpaper,border
@@ -36,6 +38,9 @@
 
 \input{../footline}
 
+\lstset{language=python, breaklines=true, showspaces=false,
+  showstringspaces=false, breakatwhitespace=true, texcl=true, escapeinside={\%*}{*)}}
+
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
 \begin{frame}
@@ -98,6 +103,96 @@ TBD
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
+\begin{frame}[fragile]
+\frametitle{Example Subclass Exception in Python}
+\ttfamily
+\begin{lstlisting}
+class Full(Exception):
+  def __init__(self, value):
+    self.value = value
+  def __str__(self):
+    return str(self.value)
+\end{lstlisting}
+\sffamily
+
+Example of raising the exception
+
+\ttfamily
+\begin{lstlisting}
+    if size == Seq.MAX_SIZE:
+      raise Full("Maximum size exceeded")
+\end{lstlisting}
+\sffamily
+
+\end{frame}
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\begin{frame}
+
+\frametitle{Exception Signaling}
+
+\begin{itemize}
+\item Useful to think about exceptions in the design process
+\item Will need to decide how exception signalling will be done
+\begin{itemize}
+\item A special return value, a special status parameter, a global variable
+\item Invoking an exception procedure
+\item Using built-in language constructs
+\end{itemize}
+\item Caused by errors made by programmers, not by users
+\item Write code so that it avoid exceptions
+\item Exceptions will be particularly useful during testing
+\end{itemize}
+
+\end{frame}
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\begin{frame}
+
+\frametitle{Assumptions versus Exceptions}
+
+\begin{itemize}
+\item The assumptions section lists assumptions the module developer is
+  permitted to make about the programmer's behaviour
+\item Assumptions are expressed in prose
+\item Use assumptions to simplify the MIS and to reduce the complexity of the
+  final implementation
+\item Interface design should provide the programmer with a means to check so
+  that they can avoid exceptions
+\item When an exceptions occurs no state transitions should take place, any
+  output is {\it don't care}
+\end{itemize}
+
+\end{frame}
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\begin{frame}
+
+\frametitle{Quality Criteria}
+
+\begin{itemize}
+\item Consistent
+\begin{itemize}
+\item Name conventions
+\item Ordering of parameters in argument lists
+\item Exception handling, etc.
+\end{itemize}
+\item Essential - omit unnecessary features
+\item General - cannot always predict how the module will be used
+\item As implementation independent as possible
+\item Minimal - avoid access routines with two potentially independent services
+\item High cohesion - components are closely related
+\item Low coupling - not strongly dependent on other modules
+\item Opaque - information hiding
+\end{itemize}
+
+\end{frame}
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
 \begin{frame}
 \frametitle{Assumptions versus Exceptions}