Boolean connectors

Boolean connectors represent the order in which tasks has to be performed.

> - The tasks can be perfomed in parallel ( note that in this cas, the task model shows no link between them)

> - Two (or more) tasks can be performed either one OR the other(s) : tasks are then linked by the boolean connector XO

- Two (or more) tasks can be performed one OR/AND the other(s) : tasks are then linked by boolean connectors OR or AND