+\section{Shared Data Sources}
+\Glspl{SDS} are an abstraction over resources that are available in the world
+or in the \gls{iTasks} system. The shared data can be a file on disk, it can be
+the time, a random integer or just some data stored in memory. The actual
+\gls{SDS} is just a record containing functions on how to read and write the
+source. In these functions the \CI{*World} is available and therefore it can
+interact with the outside world. The \CI{*IWorld} is also available and
+therefore the functions can also access other shares, possibly combining them.
+
+The basic operations for \glspl{SDS} are get, set and update. The signatures
+for these functions are shown in Listing~\ref{lst:shares}. All of the
+operations are atomic in the sense that during reading no other tasks are
+executed.
+
+\begin{lstlisting}[%
+ label={lst:shares},caption={\Gls{SDS} functions}]
+get :: (ReadWriteShared r w) -> Task r | iTask r
+set :: w (ReadWriteShared r w) -> Task w | iTask w
+upd :: (r -> w) (ReadWriteShared r w) -> Task w | iTask r & iTask w