+The coordinator is the main component of the XWCH platform. It
+controls user access and schedules jobs to workers. It provides a web
+interface for managing jobs and users, and a set of web
+services. These are user services and worker/warehouse services
+implemented using WSDL (Web Service Description Language)
+\cite{WebServ2002}, that simplifies client development for languages
+that support it (and most popular programming languages do).
+
+A worker is a Java daemon that runs on the user machine. Assumed to be
+volatile, the workers periodically report themselves to the
+coordinator, accept jobs, retrieve input, compute jobs, and store the
+results of the computation on warehouses. If the coordinator does not
+receive a signal from a worker, it will simply remove it from the
+scheduling list, and if a job had been assigned to that worker, it
+will be re-assigned to another one. A schema of the architecture is
+shown in Figure \ref{xwch}.
+
+\begin{figure}[htp]
+\label{xwch}