Are u running this code as part of an Eclipse plugin ? I think you do not.
I am not sure if that works if you are trying to access the bpel model
outside of eclipse - you'd have to export the bpel model plugin (and all
its dependencies and dependencies of dependencies) as jar files and put
them onto the classpath of your program - not sure this is feasible ?!
I suggest to create a eclipse plugin, add a dependency to bpel.model and
put that code inside of the plugin.