fail to send parameter to a function in xhtml

[handsomeli]

I can modify the properties of task and let it saved in database , the same as the sample jboss-seam-todo does:

<h:inputText value="#{task.description}" size="16" />

However, I fail to save variables of a task in database(I can only modify it in memory, next time the user login , he can not see the modification anymore!)

<h:inputText value="#{task.variables['event'].desc}" size="16" />

where 'event' come from Code:

@Stateless
@Name("eventmake")
public class MakeAction implements Make, Serializable {

 @Out(scope=ScopeType.BUSINESS_PROCESS, required=false)
 Event event = new Event();

 @CreateProcess(definition = "itsm")
 public String make() {
 return "login";
 }

 public Event getEvent() {
 return event;
 }

 public void setEvent(Event event) {
 this.event = event;
 }

}

What should i do?
I have asked this question in 'Jboss seam' , but they tell me to ask it here.
Thanks !