\section{The Backend Design}

\subsection{The Template}
OPimAccessBackend is a template interface of the Backend. 
It consists out of pure virtual functions to implement for
load, reload, save and clear. You will also need to implement
add, remove and replace.
Todo, Event and Address inherit from OPimAccessBackend to create
their Backend Type with additional functionality and also some
default implementation for some queries.

\subsection{Read Ahead}
You may implement Read Ahead or Read Behind by implementing
the specific find function. First you need to give the Frontend
a hint on how many items you want to cache and then you can call
cache to cache items.
read Ahead returns the number of Records to read behind/ahead.
