+ * Implements both archetype and implementation of a given
+ * process.
+ *
+ * At specification time, <code>executionSpec</code> represents the spec
+ * of the parameters accepted by the process, with, among others: type,
+ * default value and, optionally, possible values for each parameter. Thus
+ * ExecutionSpec might be a huge object. Note that when marshalling only
+ * a reference to a specific ExecutionSpec is stored in the XML to
+ * optimize performance and avoid redundancy between various
+ * ExecutionFlowDesciptor that might have the same ExecutionSpec.