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.