the other user's status. The mechanism behind this is called
\term{Publish-Subscribe} and is specified in XEP-0060~\cite{xep0060}. It can
be used to notify interested users about changes in personal information, and
-implements the well-known Observer pattern.
+implements the well-known Observer pattern~\cite{GOF95}.
A user publishes information by creating a \term{node} on the XMPP server, which
acts as a handle for the data. Interested users can then query the server for