Some rules of task attributes association

> - A composite and elementary task is either automatic, interactive or manual.
> - A composite automatic task contains only automatic composite and elementary) tasks.
> - A composite manual task contains only manual, composite and elementary tasks.
> - A composite interactive task contains interactive, composite and elementary tasks, and may contain automatic, composite and elementary tasks.
> - By default, the cardinality on a task is [0 , ?) for optional task and [1 , ?) for mandatory tasks.